Water Pollution

Water is a vital resource for agriculture, manufacturing and other human activities. The careless discharge of industrial effluents and other wastes in rivers & lacks may contribute greatly to the poor quality of water. Water pollution raises a great concern nowadays since water constitutes a basic necessity in life and thus, is essential to all living things. Toxic heavy metals are constantly released into the environment due to rapid industrialization and urbanization, have created a major global problem today and they are dangerous environmental pollutants due to their toxicity and strong tendency to concentrate in environment and in food chains. The main source of heavy metal contamination is from various industrial activities such as metal plating industries, batteries, mining, pigments, and stabilizers alloys, electroplating, thermal power plant, petroleum refining, paint manufacture, pesticides, pigment manufacture, printing and photographic industries etc. The important toxic heavy metals are cadmium, zinc, copper, nickel, lead, mercury and chromium etc. are often detected in industrial wastewater has always been a major environmental issue. Heavy metals are present in low concentration in wastewater and difficult to remove from water. Pollutants in industrial wastewater are almost invariably so toxic that wastewater has to be treated before its reuse or disposal in water bodies. According to Nomanbhay et al.,(2005) was reported that at least 20 metals are classified as toxic which cannot be degraded or destroyed and half of these are emitted into the environment in quantities that pose risks to human health The presence of these heavy metals in industrial wastewaters is of serious concern because they are highly toxic, non-biodegradable, carcinogen, and continuous deposition into receiving lakes, streams and other water sources within the vicinity causes bioaccumulation in the living organisms. These perhaps, could lead to several health problems like cancer, kidney failure, metabolic acidosis, oral ulcer, renal failure etc.
Heavy metals are generally considered to be those whose density exceeds 5 g per cubic centimeter. A large number of elements fall into this category, but the ones listed in table 1.1 are those of relevance in the environmental context. Cadmium is known to be toxic for living organism even if it is present in low levels such as kidney damage etc. Copper is considered as micronutrient but is extremely toxic to living organisms such as liver damage etc at higher concentrations. Arsenic is usually regarded as a hazardous heavy metal even though it is actually a semi-metal. At higher doses, heavy metals can cause irreversible brain damage. Children may receive higher doses of metals from food than adults, since they consume more food for their body weight than adults. Wastewater regulations were established to minimize human and environmental expo- sure to hazardous chemicals. This includes limits on the types and concentration of heavy metals that may be present in the discharged wastewater. The MCL standards, for those heavy metals, established by US Environmental Protection Agency (USEPA) [Barakat, (2011)].
Table 1.1 The max. contaminant level (MCL) standards for the most hazardous heavy metals by established by USEPA, CPCB, WHO..
Heavy metal Toxicities USEPA (mg/L) CPCB (mg/L) WHO (mg/L)
Arsenic Skin manifestations, visceral cancers, vascular disease. 0.050 0.1 0.5
Cadmium Kidney damage, renal disorder, human carcinogen. 0.01 0.2 0.005
Chromium Headache, diarrhea, nausea, vomiting, carcinogenic. 0.05 0.1 0.1
Copper Liver damage, Wilson disease, insomnia 0.25 2.0 0.05
Nickel Dermatitis, nausea, chronic asthma, coughing, human carcinogen. 0.20 2.0 5.0 ppb
Zinc Depression, lethargy, neurological signs and increased thirst. 0.80 5.0 5.0
Lead Damage the fetal brain, diseases of the kidneys, circulatory system, and nervous system. 0.006 0.1 5.0 ppb
Mercury Rheumatoid arthritis, and diseases of the kidneys, circulatory system, and nervous system. 0.00003 0.01 0.002
Heavy Metals
According to the Agency for Toxic Substances and Disease Registry (ASTDR) in Atlanta, Georgia, (a part of the U.S. Department of Health and Human Services), there are 35 metals of concern, with 23 of them called the heavy metals. Toxicity can result from any of these metals. This protocol will address the metals that are most likely encountered in our daily environment. Briefly covered will be four metals that are included in the ASTDR's 'Top 20 hazardous substances.' The heavy metals arsenic (1), lead (2), mercury (3), and cadmium (7) appear on this list the series may be viewed or downloaded from the ASTDR at website.
Cadmium
Cadmium is a byproduct of the mining and smelting of lead and zinc and is number 7 on ASTDR's 'Top 20 list.' It is used in nickel-cadmium batteries, PVC plastics, and paint pigments. It can be found in soils because insecticides, fungicides, sludge, and commercial fertilizers that use cadmium are used in agriculture. Cadmium may be found in reservoirs containing shellfish. Cigarettes also contain cadmium. Lesser-known sources of exposure are dental alloys, electroplating, motor oil, and exhaust. Inhalation accounts for 15-50% of absorption through the respiratory system; 2-7% of ingested cadmium is absorbed in the gastrointestinal system. Target organs are the liver, placenta, kidneys, lungs, brain, and bones [Joseph et al., (2010)].
Copper
Environmental contamination due to copper is caused by mining, printed circuits, metallurgical, fibre production, pipe corrosion and metal plating industries [Meena et al., (2005)].The other major industries discharging copper in their effluents are paper and pulp, petroleum refining and wood preserving etc. Agricultural sources such as fertilizers, fungicidal sprays and animal wastes also lead to water pollution due to copper. Copper may be found as a contaminant in food, especially shell fish, liver, mushrooms, nuts and chocolates etc. Any packaging container using copper material may contaminate the product such as food, water and drink. Copper has been reported to cause neurotoxicity commonly known as 'Wilson's disease' due to deposition of copper in the lenticular nucleus of the brain and kidney failure. In some instances, exposure to copper has resulted in jaundice and enlarged liver. It is suspected to be responsible for one form of metal fume fever. Moreover, continued inhalation of copper-containing sprays is linked to an increase in lung cancer among exposed workers.
Arsenic
Arsenic is the most common cause of acute heavy metal poisoning in adults and is number 1 on the ASTDR's 'Top 20 List.' Arsenic is released into the environment by the smelting process of copper, zinc, and lead, as well as by the manufacturing of chemicals and glasses. Arsine gas is a common byproduct produced by the manufacturing of pesticides that contain arsenic. Arsenic may be also be found in water supplies worldwide, leading to exposure of shellfish, cod, and headrace etc. Other sources are paints, rat poisoning, fungicides, and wood preservatives. Target organs are the blood, kidneys, and central nervous, digestive, and skin systems [Joseph et al., (2010)].
Lead
Lead is number 2 on the ASTDR's 'Top 20 List.' Lead accounts for most of the cases of pediatric heavy metal poisoning. It is a very soft metal and was used in pipes, drains, and soldering materials for many years. Millions of homes built before 1940 still contain lead (e.g., in painted surfaces), leading to chronic exposure from weathering, flaking, chalking, and dust. Every year, industry produces about 2.5 million tons of lead throughout the world. Most of this lead is used for batteries. The remainder is used for cable coverings, plumbing, ammunition, and fuel additives. Other uses are as paint pigments and in PVC plastics, x-ray shielding, crystal glass production, pencils, and pesticides. Target organs are the bones, brain, blood, kidneys, and thyroid gland [Joseph et al., (2010)].
Mercury
Number 3 on ASTDR's 'Top 20 List' is mercury. Mercury is generated naturally in the environment from the degassing of the earth's crust, from volcanic emissions. It exists in three forms: elemental mercury and organic and inorganic mercury. Mining operations, chloralkali plants, and paper industries are significant producers of mercury. Atmospheric mercury is dispersed across the globe by winds and returns to the earth in rainfall, accumulating in aquatic food chains and fish in lakes. Mercury compounds were added to paint as a fungicide until 1990. These compounds are now banned; however, old paint supplies and surfaces painted with these old supplies still exist. Mercury continues to be used in thermometers, thermostats, and dental amalgam. Medicines, such as mercurochrome and merthiolate, are still available. Algaecides and childhood vaccines are also potential sources. Inhalation is the most frequent cause of exposure to mercury. The organic form is readily absorbed in the gastrointestinal tract (90-100%); lesser but still significant amounts of inorganic mercury are absorbed in the gastrointestinal tract (7-15%). Target organs are the brain and kidneys [Joseph et al., (2010)].

Nickel
Electroplating is one important process involved in surface finishing and metal deposition for better life of articles and for decoration. Although several metals can be used for electroplating, nickel, copper, zinc and chromium are the most commonly used metals, the choice depending upon the specific requirement of the articles. During washing of the electroplating tanks, considerable amounts of the metal ions find their way into the effluent. Ni(II) is present in the effluents of silver refineries, electroplating, zinc base casting and storage battery etc. Higher concentration of nickel causes cancer of lungs, nose and bone., dizziness, nausea and vomiting, chest pain, tightness of the chest, dry cough and shortness of breath, rapid respiration, cyanosis and extreme weakness etc.
Chromium
Chromium is an essential element needed for human and other living organisms, which primarily involves in the action of insulin in glucose metabolism and helps transport of amino acids into the heart and liver. Its deficiency may disturb carbohydrate, lipid and protein metabolismetc. Water containing 0.5 mg/l or more chromium is considered highly toxic because it has carcinogenic and mutagenic properties. Other health problems that are caused by chromium are skin rashes, respiratory problems, weakened immune systems, kidney and liver damage, alteration of genetic material, lung cancer and death according to World Health Organization (WHO, 2007).
Zinc
Due to its remarkable resistant to atmospheric corrosion, zinc is commonly used to protect iron from rusting, in the process called galvanization. Zinc is widely used for the manufacturing of zinc white and several useful alloys such as brass, German silver, delta metal, for the preparation of gold and silver in the cyanide method, for the desilverization of lead in parks process and as an anode material in galvanic cells etc. Various zinc salts are used industrially in wood preservatives, catalysts, photographic paper, accelerators for rubber vulcanization, ceramics, textiles, fertilizers, pigments, steel production and batteries etc. [Meena et al., (2005)]. Zinc toxicity from excessive ingestion is uncommon but causes gastrointestinal distress and diarrhea.
Electroplating Industries
General
Electroplating has a long history in India; like many industrial activities, it gained momentum after Independence. Modern day electroplating started in early sixties in Mumbai with dull nickel. Bright Nickel followed soon after. Although official figures are not available, estimates indicate that in 1970, electroplating industry was considered to be in the tune of Rs. 100 million. Since then, the industry has grown steadily without facing any recession. In 1976, the first semi-automatic plant was set up in Mumbai. Currently there are more than 600 automatic plants in the country (Comprehensive Industry Document on Electroplating Industry) (COINDS), 2007.During the period 1970-85, the import restriction regulation in force led to high growth of this industry. It is estimated that electroplating industry is now worth Rs. 1000 crores (Rs.10, 000 million). This means that compounded average annual growth rate is about 16.6%. The sector employs about 1,30,000 people in approximately 12,000 organized units. The water consumption is less in electroplating industries when compared to other industries, and the effluent is more toxic than other wastes. These industries produce toxic hazardous waste containing heavy metals approximately 78,000 kg/annum which adversely effect on environment, especially on biotic components. Effluent from electroplating industry is on serious concern because just about 30-40% of the metals used during plating processes are effectively utilized i.e. plated on the articles. The remaining percentage of the metals contaminates the rinsing waters used during electroplating process. The rinse waters used during electroplating process contains about 1000 mg/L toxic heavy metals, which must be controlled to an acceptable level, in accordance to environmental regulations worldwide, before being discharged to the environment and effluents from electroplating industries is reported to contain high amounts of heavy metal ions, such as nickel, iron, lead, zinc, chromium, cadmium and copper etc. [Konstantinos et al., (2011)].These heavy metals above limits can cause adverse effect on the humans and environment.
Definition
Electroplating is one of the varieties of several techniques of metal finishing. It is a technique of deposition of a fine layer of one metal on another through electrolytic process to impart various properties and attributes, such as corrosion protection, enhanced surface hardness, lustre, color, aesthetics, value addition etc.

Fig.1.1- Electroplating effluent treatment plant
Electroplating Method
The anode and cathode in the electroplating cell are both connected to an external supply of direct current - a battery or, a rectifier. The anode is connected to the positive terminal of the supply, and the cathode (article to be plated) is connected to the negative terminal. The process of electrolysis can be explained on the basis of ionization theory. According to this theory, when the direct current is passed the electrolyte dissociates to produce positively and negatively charged ions. The positively charged (cations) ions move towards the cathode whereas negatively charged (anions) ions move towards anode. On reaching their respective electrodes, ions lose their charges and become neutral particles. The cations accept electrons from the cathode to become neutral that gets deposited in the form of metal on cathode, whereas anions gives electrons to anode to become neutral and thus forming electrolyte. The item to be coated is immersed in the bath solution as the cathode and the coating substance (the anode). However, if an inert electrode is used, the coating substance would be the metal salts in liquid form added to the solution. The metal salts subsequently dissociate into anions and cations, which then deposit onto the items to be plated.

Figure 1.2: Electroplating of a metal (Me) with copper
Electroplating process has applications in large scale manufacturing plants e.g. automobile, cycle, engineering and numerous other industries.
The basic electroplating system consists of:
1) A plating bath tilled with water containing a small amount of acid or alkali added to improve its conductivity. Thus baths used lor plating are either acid bath or alkaline bath.
2) An anode (positive electrode) - either the plating metal or an inert electrode: this is expended as the process goes on and replenished periodically
3) A cathode (negative electrode) - the item to be plated: these can he either hung inside the bath or placed in a barrel, which is rotated slowly to make the plating material deposited evenly Usually, the bath is contained in metal container, lined with acid/alkali resistant membrane e.g. pvc sheet to make it insulated trim electric circuit. The application of direct electric current across the bath solution causes the migration of
Positively charged particles (anions) towards the negative electrode (cathode) and
Negatively charged particles (cations) towards the positive electrodes (anode).
he processes are often exothermic and this leads to elevated bath temperature compared to the ambient temperature. The process efficiency depends to some degree on the.
Concentration of acid and alkali in the solution.
Temperature and.
Voltage applied across the electrodes.
The item to be coated is immersed in the bath solution as the cathode and the coating substance (the anode). However, if an inert electrode is used, the coating substance would be the metal salts in liquid form added to the solution. The metal salts subsequently dissociate into anions and cations, which then deposit onto the items to be plated. Apart from the bath chemicals and anode material, other chemical agents are used, such as brightener, wetter, booster and purifieretc.These chemical agents help to provide desired attributes, such as bright surface finish, improved and even metal deposition, depolarization, faster reaction etc. etc. The chemicals vary according to the process variants and finishing requirements for particular metal plating. By and large, most metal finishing operations typically involve 3 to 4 principal work steps or process operations, which may occur singly or in combination. These are surface preparation, pre-treatment, plating and post-treatment.
Process Chemicals
A wide variety of chemicals and substances are used, depending upon the surface properties of the objects to be electroplated, plating and finishing requirement as well as the technology / facility offered by the platters. It is very difficult to provide full details of all those used, because there are more than one commonly used process for certain metals. The general description will be covered in this section.
Solid and Hazardous Wastes
Treatment sludges contain high levels of metals, and these should normally be managed as hazardous waste or sent for metals recovery. Electrolytical methods may be used to recover metals. Sludges are usually thickened, dewatered, and stabilized using chemical agents (such as lime) before disposal, which must be in an approved and controlled landfill. The high costs of proper sludge disposal are likely to become an increasing incentive for waste minimization.
Air Emissions
A 90% recovery of the quantity of VOCs released from the process is required.
Liquid Effluents
Electroplating plants should use closed systems where feasible or attain the effluent levels presented (Sources: Pollution Prevention and Abatement Handbook, WORLD BANK GROUP Effective July 1998).
Sludges
Sludges generated from wastewater treatment. Sludges from cleaning and bath tanks and various residues like, cleaning powder. buffing compounds spent anodes and various scraps. Unused chemicals, spent resins from ion-exchange metal recovery systems also contribute to solid waste. Much of the solid waste contain hazardous and toxic substances Wherever possible, the generation of sludge should be minimized. Sludges must be dewatered and stabilized and should be disposed of in an approved, secure landfill. Leachates from stabilized sludges should not contain toxics at levels higher than those indicated for liquid effluents. Where feasible, sludges may be reused, provided that toxics are not released to the environment
'
Technologies for removal of heavy metals which are mentioned below:-
Adsorption Method
Chemical Precipitation
Membrane technology
Electro coagulation method
Ion exchange method
Coagulation method
Extraction method
Adsorption
The processes through which some of the fluid phase substances are removed by their transmission to the interface between fluid phase and a solid (separate) phase and accumulation there is called adsorption. Adsorbed material is generally classified as physisorption or chemisorption.
Physisorption or physical adsorption is a type of adsorption in which the adsorbate adheres to the surface only through Van der Waals (weak intermolecular) interactions, which are also responsible for the non-ideal behavior of real gases.
Chemisorption is a type of adsorption whereby a molecule adheres to a surface through the formation of a chemical bond, as opposed to the Van der Waals forces which cause physisorption.
Adsorption is usually described through isotherms, that is, functions which connect the amount of adsorbate on the adsorbent, with its pressure (if gas) or concentration (if liquid). One can find in literature several models describing process of adsorption, namely Freundlich isotherm, Langmuir isotherm, BET isotherm, etc.
Activated carbon produced from coconut shell (ACS) was used as adsorbent to remove Cu2+, Fe2+, Zn2+ and Pb2+ ions from electroplating industrial wastewater. The activated carbon produced was chemically activated with zinc chloride [Bernard et al., (2013)].
Chemical precipitation
Chemical precipitation is a method of wastewater treatment. Wastewater treatment chemicals are added to form particles which settle and remove contaminants. The treated water is then decanted and appropriately disposed of or reused. The resultant sludge can be dewatered to reduce volume and must be appropriately disposed of. Chemical precipitation can be used to remove metals, fats, oils and greases (FOG), suspended solids and some organics. It can also to be used to remove phosphorus, fluoride, ferrocyanide and other inorganics. It can be used on a small or large scale. A beaker full of waste, a 50,000 tank, a 1,000,000 gallon lagoon or a lake can be batch treated with chemicals. Chemical precipitation can be used in a continuous treatment system on flows ranging from a trickle to 1 gallon/minute, 1,000 gallons/minute and more. Chemical precipitation can be accomplished with very little equipment. For example, a 55 gallon drum and a mixing paddle can be used by a small discharger to treat wastewater with little capital investment. For larger volumes, a tank with a mixer and chemical feed pumps will suffice. For even larger volumes a continuous system with metering pumps, mixing tanks, a clarifier and control instrumentation can be employed. Metal precipitation is primarily dependent upon two factors: the concentration of the metal, and the pH of the water. Heavy metals are usually present in wastewaters in dilute quantities (1-100 mg/l) and at neutral or acidic pH values (pH<7.0) [Brboot et al., (2011)].
Membrane Technology
The membrane processes can be classified according to the size range of the separated species:
Reverse osmosis is used to separate dissolved salts and small organics (size under 1 nm). Example: production of drinking water from seawater or seawater desalination.
Nan filtrationis used to separate antibiotics (size under 10 nm). Example: selective demineralization of water or concentration of organic solutions.
Ultra filtrations used to separate emulsions, colloids, macromolecules or proteins (size under 100 nm).Example: treatment of pulp and paper industry's effluentsmicro-filtration is used to separate small particles, large colloids and microbial cells (size under 10 mm). Example: removal of microorganisms from the fermentation products.
Gas and vapor separation is used to isolate a gas from a mixture of gases or vapors. Example: recovery of ammonia or hydrogen from industrial gases.
Electrodialysis used to separate anions and cations by means of two charged membranes (anode and cathode). Example: production of pure water.
Membrane technology was one option for a nonpolluting process. The membrane of optimum pore sizes was capable of removing almost all pollutants without using any chemicals. Sludge obtained in the process contained only pollutant constituents in this feed stream. In order to increase the removal efficiency and reduce the operating cost, membrane technology was also used together with other treatment processes. The concentrations of heavy metals in permeate varied with feed pressure. At high pressure, the particles blocked in the pore were pushed away and discharged with the permeate. For longer time of filtration, more particles will be pushed away with the permeate. Smaller pore size membrane may be another alternative for high rejection but require a high pressure unit for operation that lead to high cost and the difficulty in controlling the process at high pressure. If the floc sizes increase by mean of good pretreatment of the wastewater operating at low pressure, lower cost and prolonged membrane life will be well achieved [Srisuwanet al., (2002)].
Electocoagulation method
Electro'coagulation is a technology that has been known for more than one hundred years. However, no systematic research has been developed that can be used to predict its chemical behavior, reactions and mechanisms, or can provide sufficient tools for the design and operation of the reactors. The technique relies on the electrochemical dissolution of sacrificial Al or Fe electrodes. The generated cations contribute by diminishing the stability of the suspended entities, by decreasing their zeta potential. Also, upon formation of hydroxide ions at the cathode, metal ions complex with iron or aluminum hydroxides, which are known to be efficient coagulants. The pollutants from many different effluents are removed by applying the principle of coagulation; however, in electro'coagulation, no use is made of a chemical coagulant. Electro'coagulation can be defined as a process in which the suspended pollutants are destabilized, emulsified or dissolved in an aqueous medium, by inducing electrical current in the water through parallel metal plates of different materials, iron and aluminum being the most commonly used. The process has been used for removal of contaminants from different wastewaters. One of the best known and most popular applications of electro'coagulation has been the treatment of wastewater from the electroplating and metal plating industries, a process that strives to remove the bulk of the soluble metals in the discharge [Sicairos al., (2011)].

Ion Exchange Method
Ion exchange can be used for the removal of undesirable anions and cations from a wastewater. Cations are exchanged for hydrogen or sodium and anions for hydroxyl ions. Ion exchange resins consist of an organic or inorganic network structure with attached functional groups. Most ion exchange resins used in wastewater treatment are synthetic resins made by the polymerization of organic compounds into a porous three-dimensional structure. Ion exchange resins are called cationic if they exchange positive ions and anionic if they exchange negative ions. Cation exchange resins are comprised of acidic functional groups, such as sulphonic groups, whereas anion exchange resins have basic functional groups, such as amine. The strength of the acidic or basic character depends upon the degree of ionization of the functional groups, similar to the situation with soluble acids or bases. Thus, a resin having sulphonic acid groups would act as a strong acid cation exchange resin. Ion exchange has a great potential to remove heavy metals from industrial wastewaters or heavy metal-containing sludge. In order to design and operate heavy metal removal processes, the equilibrium relationship between ions and resin must be known a prior. [Lee et al.,(2007)].
Coagulation method
Coagulation is the process in which particles in water are clumped together into larger particles, called floc. In a well-run water treatment plant, adjustments are often necessary in order to maximize the coagulation/flocculation process. These adjustments are a reaction to changes in the raw water entering the plant. Coagulation will be affected by changes in the water's pH, salt content, alkalinity, turbidity, and temperature.
Within the plant, two more factors can influence coagulation. Mixing effects and coagulant effects will both influence the coagulation/flocculation process. Coagulation is a unit process used for removing colloids and other suspended particles from water and wastewater. It may be employed as source treatment for the removal of contaminants such as metals, within the treatment train, or with filtration as a polishing step. Coagulation destabilizes colloidal particles by charge neutralization and promoting collisions between neutralized particles. This study to examine the effectiveness of polymer addition to coagulation process during treatment of a beverage industrial wastewater to remove some of its trace metals content such as lead, cadmium, total iron, total chromium, nickel and zinc [Amudaet al (2006)].

Extraction
Solvent extraction is a method for separating a substance from one or more others by using a solvent. It relies on variations in the solubilities of different compounds in different substances. In most cases, the substance to be extracted, which may be a solid, a liquid or a gas, is dissolved in a liquid, along with other substances, and a liquid solvent is used for the extraction ' this is sometimes called liquid-liquid extraction. The technique may also be applied to solid materials that contain compounds that need to be extracted. This method is widely used in industry, and in the laboratory for refining, isolating and purifying a variety of useful compounds Solvent extraction is now a very well-established process in hydrometallurgy. It is used for the hydrometallurgical processing of copper, nickel, cobalt, zinc, uranium, molybdenum, tungsten, vanadium, rare earths, zirconium, hafnium, niobium, tantalum, indium, gallium, germanium, the platinum group metals, boron, reprocessing nuclear fuels, purification of wet process phosphoric acid, nitric acid recovery, etc. [Silva et al., (2005)]

Selection of Process
Various chemical and physical methods have been used to remove heavy metals from waste water in the last few decades. Their advantages and limitations in application are evaluated. To highlight their removal performance, the main operating conditions such as pH and treatment efficiency are presented as well. These methods include chemical precipitation, solvent extraction, ion exchange, evaporation, reverse osmosis, electrolysis and adsorption.
From these methods, chemical precipitation, solvent extraction, ion exchange and adsorption are more commonly used which are mentioned below:-
Chemical precipitation has traditionally been used to remove heavy metal ions from wastewater with relatively high concentrations. The operation of chemical precipitation is simple but generates large quantity of sludge that is often difficult for further disposal. In addition, chemical precipitation is usually not effective to remove trace levels of metal ions from aqueous solutions.
Solvent extraction has widely been used in organ metal removal. Although the process may have fast kinetics and high capacity, solvent extraction is often costly due to the quantity and specific type of solvents needed.
Ion exchange method has commonly been used to remove metal ions from water or wastewater, but the process has slow kinetics, consumes additional chemicals, generates hazardous streams, and is not well applied to heavy metal ions due to possible problem of resin pollution.
Adsorption has been considered as, possibly, the most cost-effective method for heavy metal ion removal, especially at medium to low concentrations, because the process is simple, and chemical consumption or waste generation is not a significant issue. However, traditional adsorbents, such as activated carbon, are often not effective to adsorb heavy metal ions from water or wastewater.


Adsorption
History
Adsorption has been used for centuries. It is thought that the idea was first conceived in ancient times. However, first results or observations weren't documented until the late 1700's. At that time, adsorption was used to test the ability of charcoals and clays to uptake gases. With more research, by 1814 it was concluded by de Saussure, that all types of gases can be taken up by porous substances such as asbestos, cork, sea-foam, in addition to charcoal. By the early 1900's, the Freundlich equation was developed but was not theoretically justified. The adsorption isotherm is known as Freundlich equation, due to Freundlich's emphasis on the importance of the equation, which developed its extended use, although it was believed the equation was developed in the empirical form a decade earlier by Boedecker. Other equations were also developed and included Langmuir, Euckena, and Polanyi. Langmuir's equation was originally developed for monolayer adsorption. It is this equation that is considered as the practical equation that corresponding to an ideal and localized monolayer. Branauer, Emmett, and Teller (BET) proposed the multilayer isotherm. The BET equation uses the same assumptions as Langmuir, and assumes that Langmuir's equation applies to every adsorption layer. It was the BET theory that was the initial endeavor at creating a universal theory of physical attraction. The Langmuir and BET theories and equations are the most widely used equations for monolayer and multilayer adsorption.Adsorption is an effective purification and separation technique used in industry especially in water and wastewater treatments. A number of methods for toxic metal removal from waste water have been used, but most have several disadvantages, such as continuous input of chemicals, high cost, toxic sludge generation or incomplete metal removal but the adsorption process has been found advantageous such as: low cost of adsorbent, easy availability, utilization of industrial, biological and domestic waste as adsorbents, low operational cost, ease of operation compared to other processes, reuse of adsorbent after regeneration, capacity of removing heavy metal ions over wide range of pH and to a much lower level, ability to remove complex form of metals that is generally not possible by other methods, environmentally friendly, cost effective and technically feasible.Adsorption process is the best process for removal of metals from wastewater because it is simple, time saving and inexpensive.

2. LITERATURE REVIEW
Dutta et al., (2014) was studied on the adsorption of Cu(II) ions from electroplating industrial wastewater by using microwave assisted activated carbon. The effects of different experim ental parameters on Cu(II) adsorption were investigated. Parameters like heavy metal concentration, adsorbent dose, contact time and agitation speed have studied. It was found that 99.9 % of Cu(II) removal efficiency and 98.63% of COD removal efficiency was achieved within first 80 min of the batch adsorption study with an initial concentration of 100 mg/L, adsorbent concentration of 1 g/L, pH of 6, temperature of 30 ??C, particle size of 105 ??m and agitation speed of 200 rpm. The kinetics of the adsorption follows the pseudo second order rate kinetics. After series of batch studies it was found that the residual Cu(II) concentrations were below the WHO prescribed limit of 1.5 mg/L.
Cassava peel, the agro-waste produced from starch or the bioethanol industry, can be used as a biosorbent for the removal of heavy metals from wastewater by Phaisanthia in the year of 2013. The advantages of cassava waste are low-cost and high efficiency for heavy metals removal. However, its capability to treat real wastewater loaded with multi-heavy metals such as nickel, chromium, and copper has never been reported. The main objective of this research was to investigate the optimum factors of heavy metals removal from real electroplating wastewater using cassava peel waste. Adsorption experiments of Ni, Cu and Cr onto cassava peel waste were performed by studying some parameters including contact time, initial pH, and dose of adsorbent. In addition, two difference isotherm models including Langmuirand Freundlich were used to investigate the adsorption process. The results showed the adsorption time reached equilibrium at 300 min. Heavy metals removal efficiency of heavy metals depended on initial pH of wastewater. The result showed that pH 4 was the optimum initial pH for adsorption of Ni and Cu while pH 2 was best for the removal efficiency of chromium for cassava peel waste. The highest removal efficiency of nickel and copper using cassava peel waste was 93% and 99 %at pH 2, respectively, while chromium was 88% at pH 4. Equilibrium modeling of the adsorption isotherm showed that adsorption of three heavy metals on cassava peel waste could be described by Langmuir and Freundlich model. Furthermore, the result of the adsorption isotherm demonstrated that the ability of heavy metal removal (Kf) was in the following order; nickel > chromium > copper at pH 4, respectively. The maximum adsorption capacities for Ni and Cu were 4.33 and 0.23 mg/g at pH 4, respectively. The maximum capacity of chromium was 0.59 mg/g at pH 2.
Removal of lead (Pb) and cadmium (Cd) ions by modified shrub calotropisprocera roots materials from synthetic solution was investigated by Jothi in the year of 2013. The adsorption was found to be drastically depending on initial metal ion concentration, adsorption dosage, contact time and agitation speed. Further more the equilibrium data of adsorption are in good agreement with the models of Freundlich and Langumir. Solution containing the 1000 mg/l concentration of lead and cadmium were prepared by dissolving lead nitrate, and cadmium chloride. The percentage of Pb ion removal due to bioadsorption was calaculated as % Pb as removal =[Co- Ci/Co] x 100 %, where Ci and Co are the initial and final concentration of Pb (II) solution ( mg/L) respectively and the percentage of Cd ion removed due to bioadsorption was calculated as % Cd as removal =[Co-Ci/Co] x 100 %, where Ci and Co are the initial and final concentration of Cd (II) solution( mg/L) respectively.
In the year of 2013 by Parmar was worked on removal of cadmium from aqueous solution using cobalt silicate precipitation tube (CoSPT) as adsorbent. 50 ml of cadmium solution of desired strength (initial concentration, C0), pH and a known weight (m) of the powdered CoSPT were taken in a stoppered conical flask and shaken in a horizontal shaker for adsorb ate-adsorbent contact. Cobalt silicate precipitation tube (CoSPT), prepared through 'silica garden' route was found to be potential adsorbent for removal of cadmium from aqueous medium. Detail adsorption study of Cd(II) on CoSPT was investigated. Batch adsorption studies were carried out as a function of contact time, adsorbent dose, adsorbate concentration (50-300 mg L-1), temperature (298-323K). Cd(II) loading on CoSPT was dependent on initial Cd(II) concentration. Experimental adsorption data were modeled using Freundlich and Langmuir isotherm equations. pH variation study revealed that the adsorption increased with increase in pH of the solution. Cd(II) loading capacity of CoSPT was estimated at 319 mg g-1, which ranks high amongst efficient Cd(II) adsorbents. Adsorption data were analyzed using two kinetic models, Lagergren first order and pseudo second order. It was observed that pseudo second order rate equation represented the best correlation.
Goswami et al., (2013) was reported that fly ash as an adsorbent for removal of copper ions from synthetic wastewater. Batch experiments were carried out to investigate the effect of contact time, adsorbent dosage, and temperature. The values of optimum parameters were found. The optimum time is between 40 to 60 minutes. The adsorbent dose of 2 g/l was found to be optimum. The equilibrium adsorption data were fitted to Langmuir and Freundlichadsorption isotherm models and model parameters were evaluated. The results show that Fly ash can be employed as it is (after physical activation) to use it as low cost adsorbent for adsorption of Cu (II) from aqueous solution.
Investigated was done by Venkatesan in the year of 2013 that the removal of cadmium using wood of derris indica based activated carbon. Its adsorption capability in removal of cadmium from wastewater has been observed through batch adsorption experiments. The adsorption kinetics of this carbon for various parameters like adsorbent dosage and contact time of the cadmium ion were studied. The cadmium adsorption behavior and the effect of the initial cadmium concentration on removal efficiency were also examined. The optimum dosage of wood of derris indica based activated carbon to remove 80 mg/L of cadmium from aqueous solution 0.5gms/150 mL and the optimum contact time was 20 minutes. It was studied that up to a carbon concentration of 0.4 gm/150 ml the removal of cadmium is varying and at 0.5 g/150 ml of carbon concentration the cadmium ion removal was significant around 87.50% and from there onwards the percentage of cadmium ion removal is slightly varying and equilibrium is almost achieved at 0.5 g/150ml at a optimum time of 20 minutes. The isotherm data confirm with both Langmuir and Freundlich isotherm models.
Ossman was observed that the removal of Cd(II) ion from wastewater by adsorption onto treated old newspaper in the year of 2013. The results indicated that the adsorption of Cd(II) increased with the increasing pH, and the optimum solution pH for the adsorption of Cd(II) was found to be 6.4. Adsorption was rapid and occurred within 15 min for Cd(II) concentration range from 5 to 30 mg/L. The kinetic process of Cd(II) adsorption onto TNP was found to fit the pseudo-second-order model. The equilibrium adsorption data for Cd(II) were better fitted to the Langmuir adsorption isotherm model.
Hegazi (2013), worked on removal of heavy metals like Cu, Ni, Fe etc. from electroplating industrial wastewater by using rise husk and fly ash as adsorbents. The objective of this research is to study the utilization possibilities of less expensive adsorbents for the elimination of heavy metals from wastewater. In general the sorption consisted of 20 mg/l for the adsorbent dose in 10 mg/l of concentration metal (Cu, Ni, Fe) at an agitation rate of 200 rpm with an adsorbent time of 20 min at room temperature(25?? 3). Results showed that low cost adsorbents can be fruitfully used for the removal of heavy metals with a concentration range of 20'60 mg/l.
Production and experimental efficiency of activated carbon from local waste bamboo from wastewater was investigated by Awoyale in the year of 2013. The removal of heavy metal ions was pH dependent as the concentration of both metals after adsorption at the maximum pH of 8 was recorded to be <0.001 mg/l implying that adsorption capacity increases with increasing the pH value of the solution, and at a particular pH. The order of increase of removal percentage was Pb > Cu for both absorbents. Results showed that the best pH for adsorption was 8 with contact time of 120 minutes. When the addition of the adsorbent dose increased, the percentage removal of metal ions also increased. A maximum removal of approximately 100% was due to the assumption of approximately 0 mg/l concentration of the metals at pH 8 and dosage of 44. This was observed for both metal ions for 4g dosage. This investigation also showed that absorbent produced from bamboo is suitable for removing the Pb and Cu heavy metal ions in a typical refinery wastewater scheme. Other metal ions may be effectively removed. This is however open for further studies. For comparative study, steam activation and thermal activation should be carried out on Nigerian bamboo. Effect of various activating agents such as acetic acid, and sulphuric acid, hydrochloric acid etc and, alkaline based activating agents on the textural properties of activated carbon from Nigerian bamboo should be researched upon. The condensate obtained during the pyrolysis could be refined to yield 70% of diesel. Therefore further analysis should also be conducted.
Removal of cadmium from aqueous solution by modified low cost adsorbent in the year of 2013 was studied by Ingole. The main categories of adsorbents are carbon, agricultural wastes, industrial wastes, low grade ores, clays and lowcost synthetic oxides/hydroxides such as iron/manganese/ aluminum. Literature showed that pH is an important factor that could make a major change in the adsorption capacity. The various adsorption parameters studied to evaluate their effectson Cd(II) removal efficiency are: contact time, pH, temperature, adsorbate and adsorbent concentrations. It is evident that low-cost adsorbents have demonstrated outstanding removal capabilities for certain metal ions as compared to activated carbon. In this review, an extensive list of agricultural wastes as adsorbents including rice husk, sawdust (cedrusdeodhar wood), sawdust (Pinussylvestris), walnut sawdust, juniper fibre, sugarcane bagasse, wheat bran, cassava, tuber bark waste, cassava waste, corncorb, coir pith, and others has been compiled. Chemically modified agricultural wastes exhibit higher adsorption capacities than unmodified forms.
Ahlam et al., (2012), worked on the biosorption of Zn(II), Ni(II), Cu(II) and Cd(II) ions from aqueous solutions onto ceratoniasiliqua (Carob tree) bark has been investigated in a batch biosorption process. The biosorption process was found to be dependent on pH of solution, initial metal ion concentration, biosorbent dose, contact time and temperature. The experimental equilibrium biosorption data were analyzed by Langmuir, Freundlich, Temkin and Dubinin-Radushkevic isotherm models. The Langmuir model gave a better fit than the other three models by higher correlation coefficient, R2. The maximum biosorption capacity calculated from the Langmuir isotherm was 42.19 mg/g, 31.35 mg/g, 21.65 mg/g and 14.27 mg/g for Ni(II), Zn(II), Cu(II) and Cd(II), respectively at optimum conditions. The kinetic studies indicated that the biosorption process of the metal ions followed well pseudo-second-order model. The negative values of ??Go and the positive ??Ho revealed that the biosorption process was spontaneous and endothermic. According to the biosorption capacity, Ceratoniasiliquabark considered as an effective, low cost, and environmentally friendly biosorbent for the removal of metal ions ions from aqueous solutions.
Removal of copper from industrial wastewater by using adathodavasicas tem as low cost adsorbent was worked in the year of 2012 by Ahamed. It was used as adsorbent to remove Cu2+ from an industrial wastewater. For this purpose, high grade CuSO4.5H2O was used as heavy metal sample. Laboratory experimental investigation was carried out to identify the effect of pH (1.50 ' 5.5), agitation time (30-240 min) varying temperature (30-50??C) and varying biomass quantities (2,4,6,8,10 g/L) and other co-existing ions were also examined. The kinetics of interactions weretested with pseudo first order Lagergren equation and first order reversible 'Bhattacharya Venkobachar equation. The Langmuir & Freundlich adsorption isotherm models fitted the experimental data best with regression coefficient r2> 0.95 for the Cu(II) ions. The adsorption was endothermic and the computation of the parameters ??G??, ??H?? & ??S?? indicated that the interactions were thermodynamically favorable. The results showed that adathodavasicastem carbon (AVSC) was an effective & economical biosorbent material for the removal and recovery of heavy metal ions from waste water.
Muhammad et al., (2012) was investigated that the removal of cadmium, chromium and lead from industrial wastewater by using algae-seaweed (Ascophyllumnodosum) as adsorbent at two temperatures (23.5??C and 37??C) and four pH values (2, 5, 7 and 10). Atomic absorption spectroscopy (AAS) adsorption results show maximum adsorption capacities of 93.41% for lead at pH 2, 53.13% for cadmium at pH 10 and no adsorption for chromium throughout the pH range and temperature were found to have no significant effect on the adsorption process, especially for cadmium and lead. However, the effect of pH was significant and varied with each metal. These results were found to be comparable to results reported from previous works. The results show that the removal efficiency of each adsorbent is highly dependent on pH, and metal ion removal occurred in the preferential order lead > cadmium > chromium, depicting strong contributions from the ionic radius of each metal ion. These results demonstrate the immense potential of the adsorbent as alternatives for metal removal from industrial effluent treatment.
Abbas et al., (2012) was studied that the adsorption of lead ions from solutions containing different initial lead concentrations (100, 150 and 200 ppm pb as lead nitrate) using different particle size (140, 300 and 500 ??m) and different doses of activated carbon, sand and egg shells at different pH (4, 7 and 10) was examined. Also the metal concentration retained in the adsorbent phase (mg/g) was calculated. This method of heavy metals removal proved highly effective as removal efficiency increased with increasing adsorbent dose while it decreased with increasing metals concentration. The results revealed that of the studied adsorbents, the activated carbon showed the highest adsorption capacity and the maximum adsorption can be obtained by using particle size of 140 ??m in neutral media (pH 7). This technique might be successfully used for the removal of lead ions from liquid industrial wastes and wastewater.
Sorption study of Co (II), Cu(II) and Pb(II) ions removal from aqueous solution by adsorption on flamboyant flower (Delonix Regia) was researched by Jimoh in the year of 2012. The ability of Delonixregia (Flamboyant) flower to remove Co(II), Cu(II) and Pb(II) ions from aqueous solutions through bio-sorption was investigated in multi metal batch experiments at 32??C. The metal ions concentration was determined by atomic absorption spectroscopic (AAS) method. The influence of pH, contact time, adsorbent dosage and initial metal ion concentration were investigated. The study revealed that maximum removal of Co(II), Cu(II) Pb(II) ion from aqueous solution occurred at pH of 5. The contact time for the adsorption process was found to be at 60 minutes. The amount of metal ions adsorbed increases with increase in adsorbent dosage and initial metal ion concentration. The bio-sorption of Pb(II) and Co(II) ions exhibited pseudo-second-order kinetics models whereas Cu(II) ion followed for both pseudo first order and second order kinetics model. This study shows that Delonixregiaflower is a viable agricultural waste for the removal of Co(II), Pb(II) and Cu(II) ions from aqueous solution.
Okafor et al., (2012) was studied thatthe adsorption capacity of coconut (Cocosnucifera L.) shell for Pb2+, Cu2+, Cd2+ and As3+ from aqueous solutions. The effect of various operational parameters such as concentration, pH, temperature and sorption time on the adsorption of Pb2+, Cu2+, Cd2+ and As3+ was investigated using batch process experiments. It was found that coconut shell (CNS) can be used as a low cost adsorbent for the removal of heavy metals in aqueous solution containing low concentrations of the metals. The maximum ion adsorption capacities followed the trend Pb2+>Cu2+>Cd2+>As3+ and the percentage adsorption was found to depend on the concentration of the adsorbent present, the solution pH, temperature and the sorption. The average values of the activation energy of adsorption for coconut shell (CNS) were 7.99, 3.79, 10.24 and 53.977KJ/mol for Pb, Cu, Cd and As respectively. This shows that the adsorption of metal ions on the adsorbent is physical adsorption mechanism. Kinetic treatment of the results gave a pseudo-second order type of mechanism while the adsorption characteristics of the adsorbent followed the Freundlich adsorption isotherm.
Sheng-Fong Lo et al., (2012), worked on adsorption capacity and removal efficiency of heavy metal ions by Moso and Ma bamboo activated carbons, the carbon yield, specific surface area, micropore area, zeta potential, effects of pH value, soaking time and dosage of bamboo activated carbon were investigated. In comparison with onceactivatedbamboo carbons, lower carbon yields, larger specific surface area and micropore volume were found for thetwice-activated bamboo carbons. The optimum pH values for adsorption capacity and removal efficiency of heavymetal ions were 5.81'7.86 and 7.10'9.82 by Moso and Ma bamboo activated carbons, respectively. The optimum soaking time was 2'4 h for Pb2+, 4'8 h for Cu2+ and Cd2+, and 4 h for Cr3 by Moso bamboo activated carbons, and 1hfor the tested heavy metal ions by Ma bamboo activated carbons. The adsorption capacity and removal efficiencyof heavy metal ions of the various bamboo activated carbons decreased in the order: twice-activated Ma bamboocarbons > once-activated Ma bamboo carbons > twice-activated Moso bamboo carbons > once-activated Moso bamboo carbons. The Ma bamboo activated carbons had a lower zeta potential and effectively attracted positively chargedmetal ions. The removal efficiency of heavy metal ions by the various bamboo activated carbons decreased in the order: Pb2+> Cu2+> Cr3+> Cd2+.

Removal of lead and cadmium ions from aqueous solutions by using manganoxide mineral as adsorbent was investigated by Sonmezay in the year of 2012. The kinetics of adsorption process data was examined using the pseudo-first-order, pseudo-second-order kinetics and the intra-particle diffusion models. The rate constants of adsorption for all these kinetics models were calculated and compared. The adsorption kinetics was best described by the pseudo second-order model. The Langmuir and Freundlich adsorption isotherm models were applied to the experimental equilibrium data at different temperatures. 50 mL solution at desired concentrations which were 250 and 50 mg/L for lead and cadmium, respectively. The experimental data well fitted to Langmuir isotherm model. The maximum adsorption capacities of manganoxide mineral for lead and cadmium ions were calculated from the Langmuir isotherm and were 98 and 6.8 mg/g, respectively.
Imtiaz was studied that the synthesis of metal oxide and its application as adsorbent for treatment of wastewater effluent in the year of 2011. The method is preferred over the others for being simple and efficient giving a percentage yield of 80% and 63% for the synthesized Fe and Ni particles, respectively. The particle size ranges in diameter ~10-20nm and 40nm for iron and nickel particles, respectively. A composite of Fe and Ni in 1:1 molar ratio was also prepared by thorough mechanical grinding in agate pestle and mortar till fine, uniform, and blended powder. The characterization of synthesized materials confirmed the linkage of metal-oxygen and red shift through FTIR and UV-Visible spectroscopic technique, respectively. Sampling was done for three categories of water samples; industrial (five different industries), municipal and drinking water samples. Composite aqueous sample of each category was characterized for its physicochemical parameters like pH, EC, COD, and concentration of nitrates, sulphates, nickel, copper, cadmium and lead. The analysis presents the effluent sample of leather industry exceeding the permissible limits significantly higher for nitrates, nickel, lead, and cadmium as compared to other effluents. Whereas municipal wastewater samples depicted exceeding limits for Cu, Ni, Pb and Cd concentration. The synthesized metal particles were applied as adsorbents for the removal of different pollutants in batch experiments. The optimum removal efficiency of 97%, 96% and 98% for lead was achieved by Ni, Fe and composite particles, respectively. On comparison of efficiency of different adsorbents, Iron particles showed remarkably good efficacy for removal of metals in terms of attaining equilibrium in relatively short time (15 minutes). However, pollutants like sulphates and nitrates were more effectively reduced by Ni particles to 18 and 54 times less than the background concentration. Adsorption Kinetics and Equilibrium models were applied. The kinetics revealed pseudo second order relatively more fitted than pseudo first order. On the other hand, equilibrium models of Langmuir and Freundlich gave comparable fitness to adsorption data with coefficient of regression 0.999.
Ideriah et al., (2011), worked on removal of Pb, Cu, Ni and Cr from aqueous solution by using palms fruit fiber in removing as adsorbent. On fond that it is the function of concentration, contact time and pH variations. Palm fruit fiber from the study locations were washed with deionized water, air-dried and ground using electric grinder. The powdered fiber was sieved and treated with 0.3 M HNO3 solution for 24 h, washed with deionized water until pH 7.2 and oven dried at 60??C. The biomass was added to 1M stock metal ion solutions made from Copper sulphate, potassium dichromate, lead nitrate and nickel sulphate. The concentrations, contact time and pH of each stock solution were varied. The mixtures were shaken, filtered and analyzed by GBC avanta atomic absorption spectrophotometer version 2.02. The results showed mean percentage recovery of 51.08% Pb, 54.75% Cu, 46.96% Ni and 44.91% Cr for concentrations, 96.96% Pb, 9.79% Cu, 49.21% Ni, and 7.63% Cr with contact time, 60 ' 80 minand 87.48% Pb, 82.86% Cu, 56.71% Ni and 37.68% Cr with pH, 2 ' 4. The application of the biomass to waste water showed percentage removal of 73% Pb, 78% Cr, 82% Cu and 87% Ni. The mean percentage removal value revealed Pb as the highest and Cr as the least adsorbed. The sorption capacity of the biomass decreased with increasing concentration of metal ion but increased with decreasing pH and increasing contact time. Chemical modification of the biomass enhanced its capacity. Thus the palm fruit fiber biomass is cost effective and has great potential for use as adsorbent in removing heavy metals from aqueous solutions.
Biosorption of cadmium (Cd (II)) and arsenic (As(III)) ions from aqueous solution by tea waste biomass also a batch experimental setup was studied Kamsonlian in the year of 2011 . The effects of pH and temperature on the biosorption were studied in this work. The optimum pH for the maximum efficiency of biosorption of Cd (II) and As (III) were found to be 5.5 and 7.5, respectively. The adsorption process was endothermic in nature and spontaneous. About 95 and 84.5% removal of Cd (II) and As (III) ions was obtained at 200 mg/l of adsorbate and 6 g/l and 7 g/l of adsorbent dosage, respectively. The present study showed that tea waste biomass can serve as a good and cheap substitute for conventional carbon- based adsorbents.
Onundi was observed that the adsorption of copper, nickel and lead ions from synthetic semiconductor industrial wastewater by using palm shell activated carbon as adsorbent. In the year of 2011. Laboratory experimental investigation was carried out to identify the effect of pH and contact time on adsorption of lead, copper and nickel from the mixed metals solution. Equilibrium adsorption experiments at ambient room temperature were carried out and fitted to Langmuir and Freundlich models. Results showed that pH 5 was the most suitable, while the maximum adsorbent capacity was at a dosage of 1 g/L, recording a sorption capacity of 1.337 mg/g for lead, 1.581 mg/g for copper and 0.130 mg/g for nickel. The percentage metal removal approached equilibrium within 30 min for lead, 75 min for copper and nickel, with lead recording 100 %, copper 97 % and nickel 55 % removal, having a trend of Pb2+> Cu2+> Ni2+. Langmuir model had higher R2 values of 0.977, 0.817 and 0.978 for copper, nickel and lead respectively, which fitted the equilibrium adsorption process more than Freundlich model for the three metals.
Samorn et al., (2011), worked on the adsorption capacity of activated carbons synthesized from bamboo waste using KOH activation have greater specific surface areas (1281.7-1532.8 m2/g) and pore volumes (0.4246-0.4911 cm3/g) than a commercial activated carbon. They have iodine numbers between 811.2 and 850.4 mg/g which are greater than the standard value specified by Thai Industrial Standards Institute, implying a potential to be developed to a commercial scale. Increasing carbonization time improves the specific surface area, pore volume and iodine adsorption capacity of bamboo-derived activated carbon. Lower adsorption capacity for methylene blue compared to iodine indicates microporous structure of the activated carbons. In water treatment, the synthesized activated carbons can reduce COD, TDS, turbidity and UV254 significantly. The synthesized activated carbons have removal efficiencies comparable to the commercial activated carbon regarding to COD, TDS and turbidity.
At least 20 metals which cannot be degraded or destroyed. The important toxic metals are Cd, Zn, Pb, Cr, Cu, and Ni. Effect of pH has studied by various authors in the range of 1-12 and optimum was found in the range of 4-6 by Wasewar in the year of 2010. Effect of adsorbent dose have studied in the range of 0.2 gm/lit to 20 gm/lit. Optimum dose was varied as the studied range was varied. For pseudo-second order kinetics, the value of ksmodel parameter have found in the range of 0.0091 ' 0.1664 g/mg min and the value of initial sorption rate was observed in the range of 2 ' 26.5 mg/g min. Intra-particle diffusion model have used to present the kinetic data for the removal of zinc by adsorption onto TFW. Model parameters were found in the range of 0.0072 - 1.456 mg/g min. The negative values of free energy at all temperatures studied have been observed which is due to the fact that adsorption process is spontaneous. The positive value of free energy suggests increased randomness at the solid/solution interface during the adsorption of metal ions onto adsorbent.
Moreno et al., (2010), was studied that the removal of Mn, Fe, Ni and Cu ions from industrial wastewater by using cow bone charcoal as adsorbent. CBC has the ability to retain Mn2+, Fe2+, Ni2+and Cu2+ metals ions from aqueous solutions at the studied concentrations. Removal of heavy metals (manganese, iron, nickel and copper) from aqueous solution was possible using a activated carbon obtained from cow bone charcoal (CBC). It was seen that adsorption took place for the four metals within 25 minutes for the concentration levels studied. Under our experimental conditions and for the studied heavy metals pH plays an important role in the adsorption process, particularly on the adsorption capacity. The pH selected for an optimal rate of adsorption for all ions investigated is 5.1. It is shown that CBC has a relatively high adsorption capacity for these heavy metals; the quantities adsorbed per gram of CBC at equilibrium (qe) are 29.56 mg'g'1 for Mn2+, 31.43 mg'g'1 for Fe2+, 32.54 mg'g'1 forNi2+ and 35.44 mg'g'1 for Cu2+. This adsorption is described by an isotherm of type I and is fully matched by the Langmuir isotherm. The kinetics of the manganese, iron, nickel and copper adsorption on the CBC was found to follow a pseudo-second-order rate equation. This method has an additional advantage, as it could be applied in developing countries due to the low cost.
Removal of Cd, As, Hg, Co and Cu from industrial wastewater by using bacteria was reported by Nanda in the year of 2010. From this study five effluent samples out of nine were selected to study the removal of heavy metals by bacteria. After treatment it was found that Pseudomonas sp. and Bacillus sp. were able to remove Cd from the effluent samples with an average reduction of 56% and 44% respectively. Removal of as was recorded by Pseudomonas sp. with an average reduction recorded of 34%.Hg was removed by Bacillus sp. with an average reduction of 45%. Cu was removed by both Bacillus spandStaphylococcus sp. with an average reduction recorded of 62% and 34% respectively. Co was removed by Pseudomonas sp. and the average reduction recorded was 53%.
Slaiman et al., (2010), worked on biosorbent of England bamboo plant origin for removal of priority metal ions such as Cu and Zn from aqueous solutions in single metal state. Batch single metal state experiments were performed to determine the effect of dosage (0.5, 1 and 1.5 g), pH (3, 4, 4.5, 5 and 6), mixing speed (90, 111, 131, 156 and 170 rpm), temperature (20, 25, 30 and 35 ??C) and metal ion concentration (10, 50, 70, 90 and 100 mg/L) on the ability of dried biomass to remove metal from solutions which were investigated. Dried powder of bamboo removed (for single metal state) about 74 % Cu and 69% Zn and maximum uptake of Cu and Zn was 7.39 mg/g and 6.96 mg/g respectively, from 100 mg/L of synthetic metal solution in 120 min. of contact time at pH 4.5 and 25??C with continuous stirring at 170 rpm. Experimental results have been analyzed using Langmuir and Freundlich isotherms. Both equilibrium sorption isotherms were found to represent well the measured sorption data, but Freundlich isotherm was better than Langmuir isotherm. The effect of time was studied and the rate of removal of Cu (II) and Zn (II) ions from aqueous solution by bamboo plant was found. The rates of sorption of copper and zinc were rapid initially within 5-15 minutes and reached a maximum in about 60 minutes.
Adsorption of Cd and Pb ions from aqueous solution by using low cost adsorbent was done by Hayder in the year of 2009. Initial concentration of 1000 mg/l by the dissolving 2.75 gm of Pb(NO3)2.4H2O in 2.5 l of distilled water and 1.82 gm of Cd(NO3)2.2H2O in 2.2 l distilled water. The results showed that maximum adsorption capacity occurred at 486.9??10-3 mg/kg for Pb2+ ion and 548.8??10-3 mg/kg for Cd2+ ion. The adsorption in a mixture of the metal ions had a balancing effect on the adsorption capacity of the activated carbon. The adsorption capacity of each metal ion was affected by the presence of other metal ions rather than its presence individually. The study showed the presence of other heavy metals attribute to the reduction in the activated carbon capacity, and the adsorption process was found to obey the Freundlich isotherm for both ions.
Kannan et al., (2009) was studied on the removal of lead(II) ions by adsorption ontoindigenously prepared bamboo dust carbon (BDC) and commercial activated carbon (CAC). It has been carried out with an aim to obtain data for treating effluents from metal processing and metal finishing industries. Exactly 50 mL of lead(II) ion solution of known initial concentration was shaken with a required dose of adsorbent (CAC=4-22 g/L and BDC=10-28 g/L) of a fixed particle size (CAC=90 micron and BDC=45-250 micron) in a thermostatic orbit incubator shaker (Neolab, India) at 200 rpm after noting down the initial pH of the solution (pH = 7.2).Effect of various process parameters has been investigated by following the batch adsorption technique at 30+1??C. Percentage removal of lead(II) ions increased with the decrease in initial concentration and increased with increase in contact time and dose of adsorbent. Amount of lead(II) ions adsorbed increases with the decrease in particle size of the adsorbent. As initial pH of the slurry increased, the percentage removal increased, reached a maximum and the final solution pH after adsorption decreases. Adsorption data were modeled with the Freundlich and Langmuir isotherms, the first order kinetic equations proposed by Natarajan ' Khalaf, Lagergren and Bhattacharya and Venkobachar and intra- particle diffusion model and the models were found to be applicable. Kinetics of adsorption is observed to be first order with intra-particle diffusion as one of the rate determining steps. Removal of lead(II) ions by bamboo dust carbon (BDC) is found to be favorable and hence BDC could be employed as an alternative adsorbent to commercial activated carbon (CAC) for effluent treatment, especially for the removal of lead(II) ions.
Activated carbon prepared from Elais Guineensis kernel or known as palm kernel shell could be used as an effective adsorbent material for the treatment of copper aqueous wastewater. This work was done by Najuaet in the year of 2008. The adsorption of copper on activated carbon is found to be pH, initial concentration a nd dose dependent. The optimum conditions of copper uptake obtained from this study are: pH 5.0, initial concentration 50 mg/L and biomass loading of 1.0 g. In addition, the correlation of Temkin adsorption isotherm fits the experimental data most accurately. It was determined that the maximum adsorption capacity is 3.9293 mg/g. The material (Elais Guineensis kernel) is not only economical, but also is an agricultural waste product. Hence activated carbon derived from Elais Guineensis kernel would be useful for the economic treatment of wastewater containing copper metal.
Hefneet al., (2008), worked on the adsorption of Pb(II) from aqueous solution by using natural and treated bentonite. Lead (Pb) is one of the major environmental pollutants. Adsorption appears to be the most widely used for the removal of heavy metals. The aim of this work is to investigate the adsorption potential of commercial natural bentonite (NB) in the removal of Pb (II) ions from aqueous solution. The effects of different variables, such as, concentration of Pb, mass of NB, pH, time, NB washing and heat treatment and temperature was investigated. The bentonite sample under the heat and washed treatment are labeled as CB and WB respectively. The adsorption experiments were carried out using batch process. The equilibrium time for Pb (II) adsorption on NB was 5 min, the processes conforming to second order kinetics. NB had a much higher adsorption capacity for Pb (II) with the Langmuir monolayer capacity (qm) of 107, 110 and 120 mg g-1 at 293, 313 and 333 K respectively compared to others adsorbents. Thermodynamic parameters such as 'H??, 'S?? and 'G?? were calculated. The adsorption process was found to be endothermic and spontaneous. The enthalpy change for Pb(II) by NB adsorption has been estimated as 33 kJ mol-1 indicating that the adsorption of Pb(II) by NB corresponds to a physical reaction. The adsorption capacity of washed bentonite WB was very high compared to NB and CB.
Investigation was done for the adsorption of chromium (VI) ions on wheat bran using batch adsorption techniques by Nameni in the year of 2008. The main objectives of this study are to: 1) investigate the chromium adsorption from aqueous solution by wheat bran, 2) study the influence of contact time, pH, adsorbent dose and initial chromium concentration on adsorption process performance and 3) determine appropriate adsorption isotherm and kinetics parameters of chromium (VI) adsorption on wheat bran. The results of this study showed that adsorption of chromium by wheat bran reached to equilibrium after 60 min and after that a little change of chromium removal efficiency was observed. Higher chromium adsorption was observed at lower pH, and maximum chromium removal (87.8 %) obtained at pH of 2. The adsorption of chromium by wheat bran decreased at the higher initial chromium concentration and lower adsorbent doses. The obtained results showed that the adsorption of chromium (VI) by wheat bran follows Langmuir isotherm equation with a correlation coefficient equal to 0.997. In addition, the kinetics of the adsorption process follows the pseudo second-order kinetics model with a rate constant value of 0.131 g/m.min-1. The results indicate that wheat bran can be employed as a low cost alternative to commercial adsorbents in the removal of chromium (VI) from water and wastewater.
Akporhonor et al., (2007) was investigated that removal of Zn, Ni and Cd ions from aqueous solution by adsorption onto chemically modified maize cobs. Maize cob carbon was prepared by pyrolysis at 300 and 400oC for 35 min. This was followed by steeping in saturated ammonium chloride. The activated carbon which was characterized for bulk density, surface area, surface area charge, abrasion resistance and pH was used in the removal of Cd2+, Ni2+, Cd2+ and Zn2+. The surface areas of the maize cob carbon at 300 and 400oC were 0.010 and 0.021 g sample per mg iodine, respectively. The effectiveness of the modified maize cobs in removing the metal ions from solution was found to be Zn >Ni> Cd. The removal efficiency of the metal ions is depended on the metal ion concentration and temperature of carbonization.
Removal of Pb(II) from wastewater by using green algae cladophorafascicularis biosorption is an effective method to remove heavy metals from wastewater. In this work, Deng was found that the adsorption features of cladophorafasciculariswere investigated as a function of time, initial pH, initial Pb(II) concentrations, temperature and co-existing ions. kinetics and equilibria from batch experiments in the year of 2007. The bio-sorption kinetics followed the pseudo-second order model. Adsorption equilibria were well described by the Langmuir and Freundlich isotherm models. The maximum adsorption capacity was 198.5 mg/g at 298K and pH 5.0. The adsorption processes were endothermic and the bio-sorption heat was 29.6 kJ/mol. Desorption experiments indicated that 0.01 mol/L Na2EDTA was an efficient desorbent for the recovery of Pb(II) from biomass. IR spectrum analysis suggested amido or hydroxy, C=O and C'O could combine intensively with Pb(II).
Ngah et al., (2007), worked on removal ofCd, Cu, Pb, Zn, Ni and Cr(VI) ions from industrial wastewater by chemically modified plant waste as adsorbent. A wide range of low-cost adsorbents obtained from chemically modified plant wastes has been studied and most studies were focused on the removal of heavy metal ions such as Cd, Cu, Pb, Zn, Ni and Cr(VI) ions. The most common chemicals used for treatment of plant wastes are acids and bases. Chemically modified plant wastes vary greatly in their ability to adsorb heavy metal ions from solution. Chemical modification in general improved the adsorption capacity of adsorbents probably due to higher number of active binding sites after modification, better ion-exchange properties and formation of new functional groups that favors metal uptake. Although chemically modified plant wastes can enhance the adsorption of heavy metal ions, the cost of chemicals used and methods of modification also have to be taken into consideration in order to produce 'low-cost' adsorbents. Since modification of adsorbent surface might change the properties of adsorbent, it is recommended that for any work on chemically modified plant wastes, characterization studies involving surface area, pore size, porosity, pHZPC, etc. should be carried out. Spectroscopic analyses involving Fourier transform infrared (FTIR), energy dispersive spectroscopy (EDS), X-ray absorption near edge structure (XANES) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy are also important in order to have a better understanding on the mechanism of metal adsorption on modified plant wastes.
Adesolaet al., (2006) was reported that removal of lead ions from dilute aqueous solution using maize (Zea mays) leaf as the adsorbent. The effects of pH, initial metal ion concentration and contact time were studied at 27??C. The analysis of residual Pb (II) ions was determined using atomic absorption spectrophotometer. Maximum adsorption occurred at pH 3. The adsorption isotherms obtained at 27??C and optimum pH fitted well into both the Freundlich and Langmuir isotherms. The Freundlich and Langmuir equations are log '=0.504 log Ce+0.6939 and 1/'= 0.176/Ce'0.03, respectively. The correlation factors are 0.9959 and 0.9939. The result of the pH experiment shows that the initial pH would play a vital role in the removal of the lead ions from solution. The kinetic studies show that uptake of lead ions increases with time and that maximum adsorption was obtained within the first 30 min of the process. These results indicate that maize leaf has potential for removing lead ions from industrial wastewater.
Adsorption of Cu, Ni and Cr by modified oak sawdust was investigated by Argun in the year of 2006. This paper describes the adsorption of heavy metal ions from aqueous solutions by oak (Quercuscoccifera) sawdust modified by means of HCl treatment. The optimum shaking speed, adsorbent mass, contact time, and pH were determined, and adsorption isotherms were obtained using concentrations of the metal ions ranging from 0.1 to 100 mg L'1. The adsorption process follows pseudo-second-order reaction kinetics, as well as Langmuir and D'R adsorption isotherms. The paper discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. The maximum removal efficiencies were 93% for Cu(II) at pH 4, 82% for Ni(II) atpH 8, and 84% for Cr(VI) at pH 3.
Patil et al., (2006) was reported that the conventional powder activated charcoal (PAC) showed more sorption capacity for the removal of nickel than powder babul bark. PAC and PBB are effective at pH 8.0, hence can be efficiently used at pH 7.0 - 8.0, which is more preferable. With the application of very small dose of PBB, it is possible to reduce Ni(II) ion concentration more than 80%, and gives the nickel concentration in the effluent within limits of effluent standards for safe disposal. Recovery and regeneration of PAC is difficult, however PBB can be disposed of safely. Adsorption with low cost adsorbent is not only cheaper but requires less maintenance and supervision. Regeneration is also not required because it can be used once and burnt after drying. It is suggested that the use of powder babul bark (PBB) for removal of nickel from industrial wastewater is an effective and low cost process.
Carbon aerogel as adsorbent for removal of Cd(II), Pb(II), Hg(II), Cu(II), Ni(II), Mn(II) and Zn(II) from aqueous solution was investigated by Meena in the year of 2005. It has been found to be concentration, pH, contact time, adsorbent dose and temperature dependent. Carbon aerogel showed nearly 100% adsorptive removal of heavy metal ions under optimized conditions of dosage10 g/l for aqueous solutions containing 3 mg/l metal ions in 48 h. The adsorption parameters were determined using both Langmuir and Freundlich isotherm models. Surface complexation and ion exchange are the major removal mechanisms involved. The adsorption isotherm studies clearly indicated that the adsorptive behavior of metal ions on carbon aerogel satisfies not only the Langmuir assumptions but also the Freundlich assumptions, i.e. multilayer formation on the surface of the adsorbent with an exponential distribution of site energy. The applicability of the Lagergren kinetic model has also been investigated. Thermodynamic constant (Kad), standard free energy ('G0), enthalpy ('H0) and entropy ('S0) were calculated for predicting the nature of adsorption. The results indicate the potential application of this method for effluent treatment in industries and also provide strong evidence to support the adsorption mechanism proposed.
Nomanbhay et al., (2005) was focused on understanding biosorption process and developing a cost effective technology fortreatment of heavy metals-contaminated industrial wastewater. A new composite biosorbent has been prepared by coating chitosan onto acid treated oil palm shell charcoal (AOPSC). Chitosan loading on the AOPSC support is about 21% by weight. The shape of the adsorbent is nearly spherical with particle diameter ranging 100~150 ??m. The adsorption capacity of the composite biosorbent was evaluated by measuring the extent of adsorption of chromium metal ions from water under equilibrium conditions at 25??C. Using Langmuir isotherm model, the equilibrium data yielded the following ultimate capacity values for the coated biosorbent on a per gram basis of chitosan: 154 mg Cr/g. Bioconversion of Cr (VI) to Cr (III) by chitosan was also observed and had been shown previously in other studies using plant tissues and mineral surfaces. After the biosorbent was saturated with the metal ions, the adsorbent was regenerated with 0.1 M sodium hydroxide. Maximum desorption of the metal takes place within 5 bed volumes while complete desorption occurs within 10 bed volumes. Details of preparation of the biosorbent, characterization, and adsorption studies are presented. Dominant sorption mechanisms are ionic interactions and complexation.
Removal of Co, Cu,Zn, and Mn ions from metal finishing wastewater by using natural zeolites as adsorbent was reported by Erdem in the year of 2004. Behavior of natural (clinoptilolite) zeolites with respect to Co2+, Cu2+, Zn2+, and Mn2+ has been studied in order to consider its application to purity metal finishing wastewaters. The batch method has been employed, using metal concentrations in solution ranging from 100 to 400 mg/l. The percentage adsorption and distribution coefficients (Kd) were determined for the adsorption system as a function of sorbate concentration. In the ion exchange evaluation part of the study, it is determined that in every concentration range, adsorption ratios of clinoptilolite metal cations match to Langmuir, Freundlich, and Dubinin'Kaganer'Radushkevich (DKR) adsorption isotherm data, adding to that every cation exchange capacity metals has been calculated. It was found that the adsorption phenomena depend on charge density and hydrated ion diameter. According to the equilibrium studies, the selectivity sequence can be given as Co2+>Cu2+>Zn2+>Mn2+. These results show that natural zeolites hold great potential to remove cationic heavy metal species from industrial wastewater.
Hussein et al., (2004), worked on biosorption of for Cr(VI), Cu(II), Cd(II) and Ni(II) from industrial wastewater by using Pseudomonas species. Biosorption experiments for Cr(VI), Cu(II), Cd(II) and Ni(II) were investigated in this study using nonliving biomass of different Pseudomonas species. The applicability of the Langmuir and Freundlich models for the different biosorbent was tested. The coefficient of determination (R2) of both models were mostly greater than 0.9. In case of Ni(II) and Cu(II), their coefficients were found to be close to one. This indicates that both models adequately describe the experimental data of the biosorption of these metals. The maximum adsorption capacity was found to be the highest for Ni followed by Cd(II), Cu(II) and Cr(VI). Whereas the Freundlich constant k in case of Cd(II) was found to be greater than the other metals. Maximum Cr(VI) removal reached around 38% and its removal increased with the increase of Cr(VI) influent. Cu(II) removal was at its maximum value in presence of Cr(VI) as a binary metal, which reached 93% of its influent concentration. Concerning to Cd(II) and Ni(II) similar removal ratios were obtained, since it was ranged between 35 to 88% and their maximum removal were obtained in the case of individual Cd(II) and Ni(II).
Khan et al., (2004) was studied that the adsorption process for the removal of heavy metals from waste streams and activated carbon has been frequently used as an adsorbent. Despite its extensive use in the water and wastewater treatment industries, activated carbon remains an expensive material. In recent years, the need for safe and economical methods for the elimination of heavy metals from contaminated waters has necessitated research interest towards the production of low cost alternatives to commercially available activated carbon. Therefore there is an urgent need that all possible sources of agro-based inexpensive adsorbents should be explored and their feasibility for the removal of heavy metals should be studied in detail. The objective of this study is to contribute in the search for less expensive adsorbents and their utilization possibilities for various agricultural waste by-products such as sugarcane bagasse, rice husk, oil palm shell, coconut shell, coconut husk etc. for the elimination of heavy metals from wastewater.
Removal of cadmium and nickel from sugar industry wastewater by using bagasse fly ash was observed by Gupta in the year of 2003. Batch adsorption experiments were carried out in a series of Erlenmeyer flasks of 100 ml capacity covered with teflon sheets to prevent contamination. The effect of contact time (0'150 min), concentration (2.0' 20.0mg l_1), solution pH (2.0'9.0), adsorbent dose (2.0'20.0 g l-1), particle size (100'150, 200'250 and 300'350 mm), and temperature (30 ??C, 40??C and 50??C). The bagasse fly ash was found to be stable in water, dilute acids and bases. The composition of the adsorbent was SiO2'60.5%; Al2O3'15.4%; CaO'2.90%, Fe2O3'4.90%, MgO'0.81%. The loss on ignition was found to be 16.0% by weight. The density and porosity were found to be 1.01 g cm_3 and 0.36%fraction, respectively were studied. As much as 90% removal of cadmium and nickel is possible in about 60 and 80 min, respectively, under the batch test conditions. Effect of various operating variables, viz., solution pH, adsorbent dose, adsorbate concentration, temperature, particle size, etc., on the removal of cadmium and nickel has been studied. Maximum adsorption of cadmium and nickel occurred at a concentration of 14 and 12mg l_1 and at a pH value of 6.0 and 6.5, respectively. A dose of 10 g l_1 of adsorbent was sufficient for the optimum removal of both the metal ions. The material exhibits good adsorption capacity and the adsorption data follow the Langmuir model better then the Freundlich model. The adsorption of both the metal ions increased with increasing temperature indicating endothermic nature of the adsorption process. Isotherms have been used to determine thermodynamic parameters of the process, viz., free energy change, enthalpy change and entropy change.
Jordao et al., (2002), worked on removal of Cu, Cr, Ni, Zn, and Cd from electroplating wastewater and synthetic solutions by vermicompost of cattle manure. A glass column was loaded with vermicompost, and metal solutions were passed through it. Metal concentrations were then measured in theequate in order to evaluate the amounts retained by the vermicompost. The concentrations of Cd, Cu, Cr, Ni, Zn, Al, Ca, Mg, and Pb were determined in the vermicompost sample before and after elution with the synthetic and effluent solutions. For this purpose, portions of 50mg of the air-dried sample were individually digested at 150??C with 5ml of concentrated HNO3. A second portion of HNO3 (5 ml) was added, and the mixtures were evaporated at 150_C. Concentrated HNO3 (5 ml) and HClO4(5 ml) were then added, with the mixtures being reevaporated to near dryness and finally diluted with deionised water to 25 ml. Measurements of pH, metal concentrations, moistness, organic matter and ash contents, and infrared and XRD spectroscopy were used for vermicompst characterisation. Vermicompost residues obtained from this process were used for plant nutrition in eroded soil collected from a talus near a highway. Metal retention (in g of metal/kg of vermicompost) from effluents ranged from 2 for Cr and Zn to 4 in the case of Ni. In synthetic solutions, the values for metal retention were 4 for Cd and Zn, 6 for Cu and Ni, and 9 for Cr. The results also showed that metal concentrations in the purified effluents were below the maximum values established for waste discharges into rivers by the Brazilian Environmental Standards. The relatively high available Cd concentration of the vermicompost residue resulted in plant damage. This effect was attributed to the presence of Cd in the synthetic solution passed through the vermicompost. The data obtained do not give a complete picture of using vermicompost in cultivated lands, but such values as are determined do show that it can be suitable to remove heavy metals from industrial effluents.

EXPERIMENTAL PROGRAMME
Material and method
Babul (Acacia) wood: -As a natural adsorbent
Babul (Acacia) wood has potential to consider as adsorbent among the available natural resources because of their characteristics and easily availability. Utilization of low cost natural adsorbent for treatment of wastewater containing heavy metals in helpful as simple, effective and economically and babul (Acacia) wood were collected from local market Indore, Madhya Pradesh, India.
Babul (Acacia) wood has considered as an adsorbent for treatment process due to its potential to overcome heavy metals pollutants as well as these materials are too cheaper, renewable and abundantly available than other natural resources.
Babul wood contains arabinose, galactose, rhamnose, glucuronic acid etc.

Fig. 3.1:- Diagram for babul wood pieces
Table 3.1: Characteristics of babul wood is shown in below table:-
Parameters Values
Moisture content 15%
Crude fibre 9.2%
crude protein 13.9%
silica 0.12%
modulus of elasticity 11,060 N/mm2
density 650'830 kg/m3
Ca 2.6%
Mg 0.4%
P 0.1%
Chemicals:
All the chemicals were used of analytical reagent grade, and laboratory grade, ZnCl2, HCl, NaOH chemicals of Merck Ltd, Mumbai (India). And 'Wattman 41 filter paper' was supplied by GE Healthcare Ltd, Buckinghamshire (U.K).
Waste Water Sample:
The rinsing of material after plating operation is required to remove any plating bath solution that may be left on material. Rinsing operation emanates the largest volume of wastewater from metal plating operations. Rinse waters finally become contaminated with varying concentration of heavy metals as per the type of rinsing scheme.
A representative Electroplating waste water sample has been collected from an Electroplating industry located at Pithampur, in Dhar district of Madhya Pradesh.
Sample has been handled in such a way that there was no significant changes in composition occur before the tests are made. Effluent waste water of metal finishing stream has been taken as sample in well clean and adequate plastic container. To minimize the potential for volatilization or biodegradation between sampling and analysis, preservation of waste water sample has been made by keeping samples as cool as possible on ambient condition.
Carbonization and activation
The babul wood was cut into shorter sizes of 1-2 cm long and further reduced to desired sizes. The babul wood material was washed with distilled water for the removal of adherent extraneous matter. The washed material was dried in an oven at 105??C for 17 hours to remove moisture. The material babul wood material to be carbonized is impregnated with a boiling solution of 10 % ZnCl2 for 2 hours and soaked in the same solution for 24 hours. At the end of 24 hours, the excess solution decanted off and air dried. Then the material was carbonized in muffle furnace at 400??C. The carbonized material was cooled at room temperature for 3-5 hours before discharging into a container. It was crushed carefully into powder with the aid of crusher and sieved using sieves to get particles of uniform size and finally activated in a muffle furnace at 800??C for a period of 10 minutes in the absence of air so as to increase the surface area of the sample for adsorption purposes. It was then cooled at room temperature, washed with plenty of water to remove residual acid, dried and powdered [Baseri et al, (2012)]. Activated babul wood carbon was washed then dried for 3 hours in an oven at 150??C. The final product was then kept in an airtight polyethylene bag, ready for use.

Fig. 3.2:- Diagram for activated babul wood carbon after carbonization and activation.
Experimental procedure
To find the optimum dosage, optimum pH and optimum time for the removal of cadmium and copper using babul wood carbon as an adsorbent.
Sorption experiments
Removal of Cd and Cu onto the activated carbon prepared from babul wood was carried out by batch method and the influence of various parameters such as effect of pH; contact time and activated babul wood carbon dosage were studied. The adsorption material was powdered activated babul wood carbon produced for this study. The initial pH and temperature were measured and recorded while the effluents from the bed were collected at different intervals for two hours. For each experimental run, 1 L of metal solution was taken in an agitated vessel, pH was adjusted to the desired value, and a known amount of the activated babul wood carbon was added. This mixture was agitated at room temperature (30 ?? 1oC) and at constant rate of 100 rpm for a prescribed time to attain equilibrium. It was assumed that the applied agitator speed allows all the surface area to come in contact with heavy metals over the course of the experiments. Utilized 'Whatman 41 Filter Paper' for filtration and performed the filtration twice to ensure complete retaining of particulate matter. The concentrations of heavy metal (Cd and Cu) in the samples were measured using an atomic absorption spectrometer (AAS).
removal efficiency were all calculated using equations 1 and 2 respectively recorded metal concentration by the end of each operation was taken as initial one. Effect of pH was studied over the range of 2.5.0-10.5 and pH adjustments were made by the addition of dilute aqueous solution of 0.1M HCl and 0.1M NaOH. Effect of adsorbent dosage was studied in the range of 1.5-9.5 g/l of adsorbent at ambient temperatures and effect of contact time on adsorption was determined at different time intervals over a range of 10-60 hours.
The adsorption capacity and removal efficiency of heavy metal by babul wood activated carbons could be expressed as follows:
"AC = " ((Ci-Cf )??V)/Wg (1)
"RE (%) = " ((Ci-Cf)??100)/Ci (2)
Where
AC is the adsorption capacity of heavy metals, RE (%) is the removal efficiency of heavy metals, Ci (mg/l) and Cf (mg/l) are the concentration of heavy metals before and after adsorption experiments, respectively, V (l) is the solution volume of heavy metal concentration, and wg is the dosage of babul wood activated carbon.
Analytical Procedure for measurement of Cd and Cu by Atomic Absorption Spectroscopy
the volume of a sample (10-50 ??l) is injected into the atomizer
the sample is thermally treated and atomized (duration of measuring cycle is 1-3 min)
absorbance of the element is measured during the atomization step (total absorbance peak and peak of the background signal is recorded)
Steps of the measuring cycle in AAS (According to Richard Kopl??k- Atomic spectrometry)
Injection of the sample (and the modifier) on the wall or on the platform of the tube drying ' evaporation of solvent at a temperature slightly above the boiling point (solutions in diluted HNO3 are dried at 120 ??C); the solution must not boil; duration of drying depends on the sample volume (1-2 s/??l); inert gas flows through the tube.
Pyrolysis ' thermal decomposition at higher temperatures (300-1200??C) decomposition of sample matrix to gaseous products removed by the flow of inert gas e.g decomposition of nitrates: 2M (NO3)2 2MO + 4NO2 + O2 other processes: reaction between the analyzer and the modifier, between matrix components and the modifier duration of pyrolysis: ten seconds.
Atomization ' fast heating to high temperature (1400-2700 ??C) evaporation of the analyte, splitting molecules to atoms: MO M + O total absorbance and background signal are recorded (duration: 3-5 s) just before atomization the flow of inert gas is stopped two possibilities: atomization of the wall, or of the platform
Cleaning ' heating to very high temperature (2400-2700 ??C) for approx. 3 s; inert gas flow removes all evaporated compounds off the atomizer
Cooling of atomizer to laboratory temperature.


Fig. 3.3: Atomic absorption spectrometer block diagram
Reagents and standards
Copper stock solution
Copper, 1000 mg/L dissolve 1.000 g of copper metal in a minimum volume of (1+1) HNO3. Dilute to 1 liter with 1% (v/v) HNO3 (According to Department of energy, Environment and Chemical Engineering, Washington, University in ST. Louis)
Cadmium stock solution
Cadmium, 1000 mg/L. dissolve 1.000 g of cadmium metal in a minimum volume of (1+1) HCl. Dilute to 1 liter with 1% (v/v) HCl.
Standard solution for Cu & Cd
Standard solution for copper
For copper standard solution (1.0 mL = 0.1 mg Cu)- Dilute 100.0 mL of copper stock solution to 1 L with water (According to ASTM D1688 Standard test method for copper in water)
Standard solution for cadmium
For cadmium standard solution, dissolve 0.500 g pure Cd metal in 250 mL of 3% HCl (heat to dissolve). Cool and dilute to 500 mL with 3% HCl. Prepare an intermediate solution (10 mg/mL) by diluting 10 mL of the stock solution to 1 liter with 4% acetic acid. Pipette 3, 5, 10, 15, and 20-mL aliquots into 100-mL volumetric flasks and dilute to volume with 4% acetic acid. These cadmium working standards correspond to 0.3, 0.5, 1, 1.5, and 2 mg/mL Cd.
Procedure
Wastewater samples: Filter the sample passing through 0.45 ??m membrane filter. Instrument operation: Because of differences between makes and models of instruments, it is impossible to formulate detailed operating instructions. Follow manufacturer's recommendation for selecting proper photocell and wavelength, adjusting slit width and sensitivity, appropriate fuel and air or oxygen pressures and the steps for warm-up, correcting for interferences and flame background, rinsing of burner, igniting sample and measuring emission intensity.
Internal-standard measurement: To a carefully measured volume of sample (or diluted portion), each Cd or Cu calibration standard and a blank, add with a volumetric pipette, an appropriate volume of standard lithium solution. Measure the intensity directly.
Bracketing approach: From the calibration curve, select and prepare Cd or Cu standards that immediately bracket the emission intensity of the sample. Determine emission intensities of the bracketing standards (one Cd or Cu standard slightly less and the other slightly greater than the sample) and the sample as nearly simultaneously as possible. Repeat the determination on bracketing standards and sample. Calculate the cadmium or copper concentration by the equation formed by standard calibration curve.

Equipment used for experimental study
Muffle furnace:-
A muffle furnace is usually a front-loading box-type oven for high temperature application such as fusing glasses creating enamel coating, ceramic and soldering and brazing articles. Therefore there is no combustion involved in the temperature control of the system, which allow for much greater control of temperature uniformity and assures isolation of material being heated from the byproducts of fuel combustion.

Fig.:-3.5:- Diagram of Muffle furnace
Specifications
Heavy-duty steel exterior construction.
Interior of ceramic muffle.
Thick ceramic blanket insulation provides excellent protection from heat loss.
Temperature range upto 950oC.
Choice of digital On/Off or PID temperature control.
Electrically operated on 230 Volts AC, Single Phase.
Muffle Size (H x W x D):15 x 15 x 30 cm
Power Rating:3.3 kW
Hot air oven

Fig. 3.6: Diagram of hot air oven
There are electrical device used in experimental activity. Generally, they can be operated from 50 to 150 oC. There are some points which mentioned below:-
Thermostatically Controlled: Temperature is controlled by hydraulic type capillary thermostat to control temperature from 50??C to 250??C+1??C. an L-shaped prismatic thermometer is fitted to the unit for reading the chamber temperature.
Digitally Controlled: Temperature is controlled through a microprocessor based PID digital temperature indicator-cum-controller or through a profile digital microcontroller having 4 programmes each of 16steps (total 64 steps of ramp/soak profile), from ambient to 250??C with an accuracy of ?? 1??C. All digitally controlled ovens are fitted with air circulation fan as standard accessories.
Specications:
These are sturdy double walled units with outer chamber made of M.S. Sheet duly powder coated.
Inner chamber made up of S.S.Sheet (SS-304 grade).
Inner chamber is provided with ribs for adjusting perforated shelves to convenient height.
To work on 220/230 volts A.C.
RESULT AND DISCUSSION
Analysis of electroplating wastewater sample has been made before their treatment in order to evaluate the effluent wastewater characteristics.
Mechanism of adsorption
The mechanism of adsorption is dependent upon the size of the admolecule in comparison with the pore width due to the energetic interactions between the chosen adsorbate and the pores. Admolecules initially adsorb into the pores with the highest energy, ignoring activated diffusion effects, then adsorption proceeds via filling of progressively larger, or decreasing energy, porosity. Some pores are capable of accommodating two or three admolecules and, therefore, may undergo co-operative adsorption effects by reducing the volume element thus increasing the energy and adsorptive potential of the pore.
Adsorption is a mass transfer process which involves the accumulation of substances at the interface of two phases, such as, liquid'liquid, gas'liquid, gas'solid, or liquid' solid interface. The substance being adsorbed is the adsorbate and the adsorbing material is termed the adsorbent. The processes through which some of the fluid phase substances are removed by their transmission to the interface between fluid phase and a solid (separate) phase and accumulation there is called adsorption. Reduction in surface tension between the fluid and the solid phase as a result of the adsorption of fluid phase substances on the solid surface create required driving force for adsorption process.

Fig. 4.1:- Diagram for Adsorption on the surface of activated charcoal
To achieve a very large surface area for adsorption per unit volume, highly porous solid particles with small-diameter interconnected pores are used, with the bulk of the adsorption occurring within the pores.
Thus, during adsorption and ion exchange, the solid separating agent becomes saturated or nearly saturated with the molecules, atoms, or ions transferred from the fluid phase.
The properties of adsorbents are quite specific and depend upon their constituents. The constituents of adsorbents are mainly responsible for the removal of any particular pollutants from wastewater.
Components of fluid phase that adsorb by solid phase is called adsorbed component while the solid porous material is called as adsorbent material.
There are two principal modes of adsorption of molecules on surfaces:
Physical adsorption ( Physisorption).
Chemical adsorption ( Chemisorption).
Physical adsorption (Physisorption)
Physical adsorption occurs when the intermolecular attractive forces between molecules of a solid and the gas are greater than those between molecules of the gas itself. If the interaction between the solid surface and the adsorbed molecules has a physical nature, the process is called physisorption. In this case, the attraction interactions are van der Waals forces and, as they are weak the process results are reversible. Furthermore, it occurs lower or close to the critical temperature of the adsorbed substance.
Chemical Adsorption (Chemisorption)
If the attraction forces between adsorbed molecules and the solid surface are due to chemical bonding, the adsorption process is called chemisorption. Chemisorptions occur only as a monolayer and, furthermore, substances chemisorbed on solid surface are hardly removed because of stronger forces at stake. Under favorable conditions, both processes can occur simultaneously or alternatively. Physical adsorption is accompanied by a decrease in free energy and entropy of the adsorption system and, thereby, this process is exothermic.

Table 4.1:-Difference between physical adsorption and chemical adsorption

The amount of material which is adsorbed on the surface at a particular temperature depends upon the amount of that substance in the gas or liquid phase which is in contact with the surface, and this dependence is called the adsorption isotherm. The isotherm is useful in determining the interactions between the adsorbate and the adsorbent. The extent of adsorption is usually measured by coverage, ?? which is given by
?? = (number of surface sites occupied)/ (total number of surface sites) (4.1)
Langmuir isotherm is concerned with the monolayer coverage of the solid surface by the adsorbate. It assumes that the surface consists of sites onto which the adsorbate can adsorb, and that each site can accommodate one entity at a time. The binding energy at each site is also assumed to be equivalent.
?? = Kp (4.2)
Molecule + Surface site Adsorbed molecule
Where
"K = " "kads" /"kdes" (4.3)
When used in to describe the adsorption of solutes from solution, the Langmuir equation is as follows
"qe = " "qmKLCe" /(1+ "KLCe" ) (4.4)
"qe = " "w" /"m" (4.5)
1/"qe" = 1/"qm" + 1/"qmKL" 1/"Ce" (4.6)
Where Ce is the equilibrium concentration of the adsorbate in the solution, w is the mass of the adsorbate, m is the mass of the adsorbent, qm and kL are Langmuir constants. Hence one should be able to determine qm and kL from a linear plot of 1/qe versus 1/Ce.
When the amount of adsorbent in contact with the solid surface is very low, the linear equation which is used to explain Langmuir isotherm might not be sufficient to explain the adsorption behaviour. For such cases the expression used for Freundlich adsorption isotherm might be more appropriate to use. This modified isotherm is to be expected if the binding energy changes continuously from site to site on solid surfaces.
?? = Kp1/?? (4.7)
When used to describe the adsorption of solutes from solution, this equation would take the form
n = kc1/ ?? (4.8)
To test for agreement one would plot log n against log c and use the slope to evaluate ?? which is an empirical constant which lies between 2 and 10. It has been found that Langmuir and Freundlich isotherms, as well as others, have been very useful in explaining the adsorption behaviour of adsorbate on solid surfaces.

Analysis of electroplating wastewater sample has produced following result.
Table 4.2: Analysis of pretreated electroplating wastewater sample
S. N. Property Report
1 pH 3.0
2 Odor Unpleasant
3 Color Dark black
4 Total solid 23822
5 Dissolved solid 23220
6 Suspended solid 602
7 Conductivity 24170
8 COD 3450
9 Cadmium 1021
10 Copper 896
Note: - All the parameters are expressed in mg/L except pH
Effect of various parameters on heavy metals removal
Effect of pH
pH is one of the most important parameters controlling uptake of heavy metals from wastewater.
It has been reported that the removal efficiency of heavy metals by adsorption is highly dependent on pH values. Hence in order to access the effect of pH on the performance of babul wood, removal efficiency of heavy metals has been examined at different pH range of 2.5-10.5. The COD reduction with pH using constant mass loading of 5.5 g/L of adsorbent material over constant time period of 2 hours is presented in fig. 4.3 and it may be that within pH 2.5 to 10.5, the COD reduction don't change considerably except pH 5.5.
It was also seen that heavy metals removal efficiency of cadmium and copper are maximum at pH 5.5. The analysis data represent the effect of pH on heavy metals removal efficiency of adsorbent.
Table 4.3: Shows the effect of pH on heavy removal by adsorption system.
S. N. pH COD % Cadmium removal % Copper removal
1 2.5 3250 67.11 78.21
2 4.5 2879 74.22 82.11
3 5.5 1511 76.92 89.01
4 8.5 1835 68.53 85.05
5 10.5 2238 63.86 80.23

Fig. 4.2: Effect of pH on percentage heavy removal by adsorption system.

Fig. 4.3: Variation of the value of COD with pH of industrial wastewater sample.


Effect of mass dosages of babul wood carbon on adsorption
The concentration profile of cadmium and copper revealed that the heavy metals removal efficiency has greatly affected by mass dosages of babul wood carbon, but it was also concluded that it is not significant beyond a dosage of 5.5 g/l, beyond this limit of dosing the removal efficiency of heavy metals is not function of mass loading of adsorbent. It is obtained that when using babul wood activated carbon. This alkaline character is believed to be a result of the alkalinity of the carbon, which increases the solution's pH.
Table 4.4: Effect of mass loading of babul wood carbon on adsorption process.
S. N. Mass dosages in g/l pH
1 1.5 3.2
2 3.5 3.5
3 5.5 3.7
4 7.5 4.1
5 9.5 4.2


Fig. 4.4: Effect of mass dosages of babul as potential adsorbent on pH.
The effect of mass dosages of adsorbent on adsorptive treatment of electroplating wastewater had been seen by their heavy metals removal efficiencies. Result shows in below table 4.5:-
Table 4.5: Effect of mass dosages of adsorbent by their heavy metals removal efficiencies.
S. N. Adsorbent dosages in g/l % Cadmium removal % Copper removal
1 1.5 54.22 70.54
2 3.5 64.26 82.39
3 5.5 76.92 89.01
4 7.5 77.95 90.21
5 9.5 81.61 91.61


Fig 4.5: The effect of mass dosages of adsorbent on adsorptive treatment of electroplating wastewater of pH value 5.5on percentage metal removal by adsorption method.
Effect of Contact Time
As contact time increases, concentration of cadmium and copper in the solution decreased rapidly at the beginning and later slows down until it remained constant at about 48 hours, which was then taken as the equilibrium time (Fig.4.6). This indicates that the removal of cadmium and copper ions by activated babul wood carbon was very rapid at the beginning. Most of the maximum percent cadmium and copper removal was attained after about 24 hours. The increasing contact time further do not removed the cadmium and copper and it remains constant after equilibrium reached in 48 hours.
Table 4.6:-Effect of total time of adsorbent by their heavy metals removal efficiencies.
S. N. Contact time (hr) % Cadmium removal % Copper removal
1 12 55.12 67.15
2 24 76.92 89.01
3 36 81.21 90.02
4 48 84.28 93.85
5 60 84.29 93.88


Fig. 4.6: Effect of contact time on the removal of cadmium and copper by activated babul wood carbon.

Develop model equation
Equilibrium Study
Adsorption isotherms are mathematical models that describe the distribution of the adsorbate species among liquid and adsorbent, based on a set of assumptions that are mainly related to the heterogeneity/homogeneity of adsorbents, the type of coverage and possibility of interaction between the adsorbate species. Adsorption data are usually described by adsorption isotherms, such as Langmuir and Freundlich isotherms. These isotherms relate metal uptake per unit mass of adsorbent, qe, to the equilibrium adsorbate concentration in the bulk fluid phase Ce.
Langmuir isotherm
The Langmuir model is based on the assumption that the maximum adsorption occurs when a saturated monolayer of solute molecules is present on the adsorbent surface, the energy of adsorption is constant and there is no migration of adsorbate molecules in the surface plane. The Langmuir isotherm is given by
"qe = " "qmKLCe" /(1+ "KLCe" ) (4.3.1)
"1/qe = " "m" /w (4.3.2) 1/"qe" = 1/"qmKL" 1/"Ce" +1/"qm" (4.3.3)
Where w and m are mass of solute adsorbed and mass of adsorbent, qmandKLare the Langmuir constants, representing the maximum adsorption capacity for the solid phase loading and the energy constant related to the heat of adsorption respectively. qm is calculated by data of slope of eq. 4.3.3
For equilibrium study mass of adsorbent was kept constant and adsorbate concentration was carried. After 24 hrs the Cu concentration and Cd concentration in adsorbent and liquid was determined. It is already shown that 48 hrs is the time to reach the equilibrium (Plot between 1/Ce and 1/qe is shown in Fig. 4.7. From the slop and intercept data the value of qm evaluated.
Table 4.7: Data for Langmuir isotherm from babul wood carbon (a) Cu, (b) Cd.
(a)
m (g) w (g) 1/Ce 1/qe
1.5 0.6320384 2.39443313 2.373273523
3.5 0.7382144 4.678591709 4.741170045
5.5 0.7975296 8.099181074 6.896295761
7.5 0.8082816 9.214504597 9.278944368
9.5 0.8208256 10.91895113 11.5737131

(b)
m (g) w (g) 1/Ce 1/qe
1.5 0.55359 1.184359983 2.709605117
3.5 0.65609 1.79798545 5.334596566
5.5 0.78535 3.332755633 7.003218425
7.5 0.79587 3.535147392 9.423655511
9.5 0.833238 4.437737901 11.40130294

"1/Ce = " "w" /"Co - w" (4.3.4)
Co is initial Cu concentration. 0.896 g/l
Co is initial Cd concentration. 1.021 g/l
(a)

(b)

Figure 4.7: Langmuir plot for adsorption of Cu on (a) Cu, (b) Cd
Co is initial Cu concentration. 0.896 g/l
Cois initial Cd concentration. 1.021 g/l
It can be seen from figure above that the isotherm data fits the Langmuir equation well (R2=0.965 and 0.996). The values of qm found from slope was 2.341 mg/g for Cu and 1.366 mg/g for Cd. It implies monolayer adsorption capacity is (2.341 mg Cu and 1.366 mg Cd) /g of babul wood carbon.
Freundlich Isotherm
The Freundlich isotherm model is an empirical relationship describing the adsorption of solutes from a liquid to a solid surface and assumes that different sites with several adsorption energies are involved. Freundlich adsorption isotherm is the relationship between the amounts of Cu and Cd adsorbed per unit mass of adsorbent w/m and the concentration of the Cu and Cd at equilibrium Ce
qe = Kf.(Ce)1/n (4.3.2)
The logarithmic form of the equation becomes
lnqe = lnKf + (1/n) lnCe (4.3.3)
Where w and m are mass of solute adsorbed and mass of adsorbent, Kf and n are the Freundlich constants, the characteristics of the system. Kf and n are the indicators of the adsorption capacity and adsorption intensity respectively. The ability of Freundlich model to fit the experimental data was examined. For this case, the plot of lnCe vs. ln1/qe was employed to generate the intercept value of Kf and the slope n. The magnitudes of Kf and n shows easy separation of Cu and Cdfrom the aqueous solution and indicatefavourable adsorption.The intercept Kfvalue is an indication of the adsorptioncapacity of the adsorbent; the slope 1/nindicates the effect of concentration on theadsorption capacity and represents adsorption intensity.The Freundlich isotherm is morewidely used but provides no information on the monolayer adsorption capacity incontrast to the Langmuir model. Data of lnqe and lnCe is plotted in Fig. The value of Kf and n was evaluated.
Table 4.8: Data for Freundlich isotherm (a) Cu, (b) Cd.
(a)
m (g) w (g) Ce lnCe lnqe
1.5 0.63204 0.417635384 -0.8731 -0.86427
3.5 0.73821 0.213739531 -1.543 -1.55628
5.5 0.79753 0.123469273 -2.0918 -1.93098
7.5 0.80828 0.108524554 -2.2208 -2.22775
9.5 0.820826 0.091583888 -2.3905 -2.44874

(b)
m (g) w (g) Ce lnCe lnqe
1.5 0.55359 0.84434 -0.1692 -0.9968
3.5 0.65609 0.55618 -0.5867 -1.67421
5.5 0.78535 0.30005 -1.2038 -1.94637
7.5 0.79587 0.28287 -1.2628 -2.24322
9.5 0.833238 0.22534 -1.4901 -2.43373

(a)

(b)

Figure 4.8: Freundlich plot for adsorption of Cu on (a) Cu, (b) Cd
It can be seen from figures above that the isotherm data fits the Freundlich equation well (R2=0.982 and 0.942).

Study of adsorption kinetics
In order to investigate the controlling mechanism of adsorption processes such as mass transfer and chemical reaction, the pseudo-first-order and pseudo-second order equations can be applied to model the kinetics of Cu and Cd adsorption onto activated babul wood powdered with Zncl2.
The pseudo first order rate equation is given as
ln Ct = ln Co - kadt (4.4.1)
Cw = Co - Ct (4.4.2) Where Co and Ct are the initial concentration and concentration of solution (mg/l) at timet, Cw is mass of Cu and Cd (mg) adsorbed, at equilibrium respectively and kadis the rate constant of the pseudo-first-order adsorption process (min-1).Straight line plots of lnCt againstt were used to determine the rate constantkad , and the correlation coefficientsR2.
Since R2 has low value of 0.9325 (for babul wood carbon), it has found from Fig. that adsorption of Cu and Cd on babul wood carbondid not follow pseudo first-order kinetics. It needs to check pseudo second-order kinetics.
Table 4.9 Data for pseudo first order kinetics.

Babul wood carbon
t (hrs) Ct (mg/l) ln Ct
12 1.5 0.405465108
24 3.5 1.252762968
36 5.5 1.704748092
48 7.5 2.014903021
60 9.5 2.251291799

Figure 4.9Pseudo first order kinetics for Cu and Cd adsorption.
Now pseudo-second-order rate equation is given as
t/Cw = 1/h+1/Co (4.4.3)
Where h=kadCo2can be regarded as the initial adsorption rate as t'0 and kadis the rate constant of pseudo second order adsorption (mg/l.min). The plot t/Cwversus t should give a straight line if pseudo-second-order kinetics is applicableand Co, kadand h can be determined from the slope andintercept of the plot, respectively.
The plot of t/Cwversus t for pseudo second order model yields very good straight lines as compared to the plot ofpseudo-first order with correlation coefficient (R2=0.997). This suggests that the adsorption of Cu and Cdbybabul wood carbonfollows the pseudo-second-order kinetic model.
Table 4.10 Data for pseudo second order kinetics.
Cu Cd
t (hrs) Cw (mg/l) t/Cw Cw (mg/l) t/Cw
12 0.601664 19.94468674 0.56278 21.3229
24 0.7975296 30.09292696 0.78535 30.5595
36 0.7975296 45.13939044 0.82915 43.4177
48 0.840896 57.08196971 0.8605 55.7816
60 0.8411648 71.32966097 0.8606 69.7187

Figure 4.10Pseudo second order kinetics for Cu and Cd adsorption.
The value of h and Co evaluated are presented in Table 4.11 below
Adsorbent kad(mg/l.min) Co (mg/L) R2 h
Babul wood carbon (Cu) 0.00000115 896 0.997 0.9248
Babul wood carbon (Cd) 0.000000943 1021 0.9956 0.9834

Comparison of various adsorbents
According to various authors, they have investigated different different types of natural adsorbents for removal of heavy metals like Cu, Cd, Cr etc. and comparison of maximum percentage adsorption capacities of heavy metals are shown below tables with respect the value of pH.:-
Table 4.11 Comparison of various adsorbents
Name of adsorbent pH Percentage Adsorption capacity (Cu) Percentage Adsorption capacity (Cd) Reference
microwave assisted activated carbon 6 99.9 Dutta et al., (2014)
cassava waste 2 99 Phaisanthia,,2013
bagasse fly ash 6 90 Gupta, 2013
Ulgae-seaweed 10 53.13 Muhammad et al., (2012)
Local waste bamboo 8 100 Awoyale, 2012
flamboyant flower 5 Jimoh., 2012
Palms fruits fiber 3 82 Ideriah., (2011)
palm shell activated carbon 5 97 Onundi., 2011
tea waste biomass 5.5 95 Kamsonlian., 2011
cow bone charcoal 5.1 Moreno et al., (2010)
modified oak sawdust 4 93 Argun., 2006
Babul wood carbon 5.5 89.01 76.92 Present study

Hence activated carbon derived from babul wood would be useful for the economic treatment of wastewater containing copper and cadmium metal.

Adsorption column design for adsorption
Batch type sorption is usually limited to the treatment of small volumes of effluent, whereas adsorption column systems have an advantage over this limitation. In adsorption column the adsorbate is continuously in contact with a given quantity of fresh adsorbent thus providing the required concentration gradient between adsorbent and adsorbate for adsorption.
For the adsorption columns design calculations to be carried out, certain assumptions were made. The assumptions made were that:
The process is isothermal
There are no chemical reactions in the column
The bed is homogenous
The concentration gradient in the radial direction of the bed is negligible
The flow rate is constant and does not change with column position.
For powdered babul wood application, isotherm adsorption data can be used in conjunction with a material mass balance analysis to obtain an approximate estimated amount of babul wood carbon that must be added. Because of many unknown factors involved, column and bench scale tests are recommended to develop the necessary data.
If mass balance is written around contactor after equilibrium has been reached.
Amount adsorbed = initial amount of adsorbate present ' final amount of adsorbate present
(4.6.1) "qem = VCo??VCe" (4.6.2)
Where
qe= adsorbent phase concentration after equilibrium, mg adsorbate/g adsorbent
m= mass of adsorbent, g
V= volume, m3
Co= initial concentration of adsorbate, mg/l
Ce= final equilibrium concentration of adsorbate after adsorption has occurred, mg/l
It should be noted that qe is in equilibrium with C if eqn (4.6.2) is solved for qe
"qe = " "V(Co-Ce)" /"m" (4.6.3)
From eqn (4.6.3) is written as follows
"V" /"m" " = " "qe" /"Co-Ce" (4.6.4)
"V" /"m" is the specific volume.
Adsorber column. The volume of the adsorber column can be estimated through the following expression:
V = A*H (4.6.5)
Where
V is the volume of column in m3
A area of adsorber m2
H is Height of column in meter

Contact Time.
"EBCT = " V/Q"e" "= " (LA )/Q"e" (15)
Where
V = bulk volume of babul wood carbon in contactor, m3
A = cross-sectional bed area, m2
L = bed depth, m (ft)
Q = volumetric flow rate, m3/hr
As calculated Contact time is 24 hrs
Column internal diameter is 1.9 meter
Flowrate, Q = 1.09 m3/hr
Area = A=??/(4 )Di2 (4.6.6)
Area, A = 2.54 m2
EBCT (Empty bet contact time) = 24 hrs
Bed height, L = 9 m
Flow rate = velocity*Area
= v*A (4.6.7)
Velocity, v = 0.37 m/hr

The height of the adsorber column, H, should be higher than 1.35 m in order to accommodate a packed bed long (According tothe Royal Society of Chemistry 2004).

Height of column, H = 1.35*9
H = 12.5 m
Volume, V=A*H
= 2.54*12.5
= 36 m2
Column Height, H = 12.5m
Column Diameter, Di = 1.9 m
Bed Height, L = 9 m
Flow rate, Q = 1.09 m3/hr
Contact time = 24 hrs
Area of Column, A= 36 m2
Wastewater flow rate of 1.09 m3/hr is to be treated with activated babul wood carbon to remove heavy metals (copper and cadmium) by using adsorption column and diameter of column 1.9 m.

Optimization of data
1 L of metals solution is taken for batch experiment at ambient temperature and at constant 100 rpm. In this experiment optimum value of various parameter such as pH, contact time and adsorbent dosage was obtained 5.5, 24 hr and 5.5 g/l respectively, which are mentioned below table 4.13:-
Name of parameters Optimum value
pH 5.5
Adsorbent dosage 5.5
Contact time 24 (hrs)

Also verified experimental optimized data in C++ software which are mentioned below:-
#include<iostream.h>
#include<conio.h>
#include<iomanip.h>
#include<math.h>
void main ()
{
clrscr ();
float pH,CT,AD;
//optimization of pH;
cout<<" enter the value of pH="<<endl;
cin>> pH;
if (pH>5.5 && pH<5.5)
cout<<"condition is not not optimized"<<endl;
else
cout<<"condition is optimized"<<endl;
//optimization of CT
cout<<"enter the value of CT="<<endl;
cin>>CT;
if(CT>24 && CT<24)
cout<<"condition is not optimized"<<endl;
else
cout<<"condition is optimized"<<endl;
//optimization of AD
cout<<"enter the value of AD="<<endl;
cin>>AD;
if (AD>5.5 && AD<5.5)
cout<<"condition is not optimized"<<endl;
else
cout<<"conditionis optimized"<<endl;
cout<<"condition is finely optimized";
getch();
}

run
enter the value of pH=
5.5
condition is optimized
enter the value of CT=
24
condition is optimized
enter tHe value of AD=
5.5
condition is optimized
condition is finely optimized

5. CONCLUSION
Following conclusions have been made from the experiment results:-
Treatment of electroplating wastewater by adsorption process using babul wood carbon as an adsorbent has been found effective.
The results show that the removal efficiency of each adsorbent is highly dependent on pH, adsorbent dosage and contact time.
It has obtained that the maximum COD reduction at mass dosage of 5.5 g/l with pH 5.5.
Adsorption of cadmium and copper increased with increase in pH reached maximum at 5.5 pH.
Adsorptive capacity and metal removal efficiency of adsorbent babul wood increased with contact time and reached maximum near at 24 hours.
Adsorption of cadmium and copper on babul wood (treated) were obtained maximum capacity of 1.366 mg/g and 2.341 mg/g respectively at pH 5.5.

Further research needs are identified in the following areas
The effect of pH of low cost adsorbent on the adsorption of heavy metals can be studies.
The effects of carbon content of low cost adsorbent on the adsorption of heavy metals can be studies.

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INTRODUCTION
General
Water is a vital resource for agriculture, manufacturing and other human activities. The careless discharge of industrial effluents and other wastes in rivers & lacks may contribute greatly to the poor quality of water. Water pollution raises a great concern nowadays since water constitutes a basic necessity in life and thus, is essential to all living things. Toxic heavy metals are constantly released into the environment due to rapid industrialization and urbanization, have created a major global problem today and they are dangerous environmental pollutants due to their toxicity and strong tendency to concentrate in environment and in food chains. The main source of heavy metal contamination is from various industrial activities such as metal plating industries, batteries, mining, pigments, and stabilizers alloys, electroplating, thermal power plant, petroleum refining, paint manufacture, pesticides, pigment manufacture, printing and photographic industries etc. The important toxic heavy metals are cadmium, zinc, copper, nickel, lead, mercury and chromium etc. are often detected in industrial wastewater has always been a major environmental issue. Heavy metals are present in low concentration in wastewater and difficult to remove from water. Pollutants in industrial wastewater are almost invariably so toxic that wastewater has to be treated before its reuse or disposal in water bodies. According to Nomanbhay et al.,(2005) was reported that at least 20 metals are classified as toxic which cannot be degraded or destroyed and half of these are emitted into the environment in quantities that pose risks to human health The presence of these heavy metals in industrial wastewaters is of serious concern because they are highly toxic, non-biodegradable, carcinogen, and continuous deposition into receiving lakes, streams and other water sources within the vicinity causes bioaccumulation in the living organisms. These perhaps, could lead to several health problems like cancer, kidney failure, metabolic acidosis, oral ulcer, renal failure etc.
Heavy metals are generally considered to be those whose density exceeds 5 g per cubic centimeter. A large number of elements fall into this category, but the ones listed in table 1.1 are those of relevance in the environmental context. Cadmium is known to be toxic for living organism even if it is present in low levels such as kidney damage etc. Copper is considered as micronutrient but is extremely toxic to living organisms such as liver damage etc at higher concentrations. Arsenic is usually regarded as a hazardous heavy metal even though it is actually a semi-metal. At higher doses, heavy metals can cause irreversible brain damage. Children may receive higher doses of metals from food than adults, since they consume more food for their body weight than adults. Wastewater regulations were established to minimize human and environmental expo- sure to hazardous chemicals. This includes limits on the types and concentration of heavy metals that may be present in the discharged wastewater. The MCL standards, for those heavy metals, established by US Environmental Protection Agency (USEPA) [Barakat, (2011)].
Table 1.1 The max. contaminant level (MCL) standards for the most hazardous heavy metals by established by USEPA, CPCB, WHO..
Heavy metal Toxicities USEPA (mg/L) CPCB (mg/L) WHO (mg/L)
Arsenic Skin manifestations, visceral cancers, vascular disease. 0.050 0.1 0.5
Cadmium Kidney damage, renal disorder, human carcinogen. 0.01 0.2 0.005
Chromium Headache, diarrhea, nausea, vomiting, carcinogenic. 0.05 0.1 0.1
Copper Liver damage, Wilson disease, insomnia 0.25 2.0 0.05
Nickel Dermatitis, nausea, chronic asthma, coughing, human carcinogen. 0.20 2.0 5.0 ppb
Zinc Depression, lethargy, neurological signs and increased thirst. 0.80 5.0 5.0
Lead Damage the fetal brain, diseases of the kidneys, circulatory system, and nervous system. 0.006 0.1 5.0 ppb
Mercury Rheumatoid arthritis, and diseases of the kidneys, circulatory system, and nervous system. 0.00003 0.01 0.002
Heavy Metals
According to the Agency for Toxic Substances and Disease Registry (ASTDR) in Atlanta, Georgia, (a part of the U.S. Department of Health and Human Services), there are 35 metals of concern, with 23 of them called the heavy metals. Toxicity can result from any of these metals. This protocol will address the metals that are most likely encountered in our daily environment. Briefly covered will be four metals that are included in the ASTDR's 'Top 20 hazardous substances.' The heavy metals arsenic (1), lead (2), mercury (3), and cadmium (7) appear on this list the series may be viewed or downloaded from the ASTDR at website.
Cadmium
Cadmium is a byproduct of the mining and smelting of lead and zinc and is number 7 on ASTDR's 'Top 20 list.' It is used in nickel-cadmium batteries, PVC plastics, and paint pigments. It can be found in soils because insecticides, fungicides, sludge, and commercial fertilizers that use cadmium are used in agriculture. Cadmium may be found in reservoirs containing shellfish. Cigarettes also contain cadmium. Lesser-known sources of exposure are dental alloys, electroplating, motor oil, and exhaust. Inhalation accounts for 15-50% of absorption through the respiratory system; 2-7% of ingested cadmium is absorbed in the gastrointestinal system. Target organs are the liver, placenta, kidneys, lungs, brain, and bones [Joseph et al., (2010)].
Copper
Environmental contamination due to copper is caused by mining, printed circuits, metallurgical, fibre production, pipe corrosion and metal plating industries [Meena et al., (2005)].The other major industries discharging copper in their effluents are paper and pulp, petroleum refining and wood preserving etc. Agricultural sources such as fertilizers, fungicidal sprays and animal wastes also lead to water pollution due to copper. Copper may be found as a contaminant in food, especially shell fish, liver, mushrooms, nuts and chocolates etc. Any packaging container using copper material may contaminate the product such as food, water and drink. Copper has been reported to cause neurotoxicity commonly known as 'Wilson's disease' due to deposition of copper in the lenticular nucleus of the brain and kidney failure. In some instances, exposure to copper has resulted in jaundice and enlarged liver. It is suspected to be responsible for one form of metal fume fever. Moreover, continued inhalation of copper-containing sprays is linked to an increase in lung cancer among exposed workers.
Arsenic
Arsenic is the most common cause of acute heavy metal poisoning in adults and is number 1 on the ASTDR's 'Top 20 List.' Arsenic is released into the environment by the smelting process of copper, zinc, and lead, as well as by the manufacturing of chemicals and glasses. Arsine gas is a common byproduct produced by the manufacturing of pesticides that contain arsenic. Arsenic may be also be found in water supplies worldwide, leading to exposure of shellfish, cod, and headrace etc. Other sources are paints, rat poisoning, fungicides, and wood preservatives. Target organs are the blood, kidneys, and central nervous, digestive, and skin systems [Joseph et al., (2010)].
Lead
Lead is number 2 on the ASTDR's 'Top 20 List.' Lead accounts for most of the cases of pediatric heavy metal poisoning. It is a very soft metal and was used in pipes, drains, and soldering materials for many years. Millions of homes built before 1940 still contain lead (e.g., in painted surfaces), leading to chronic exposure from weathering, flaking, chalking, and dust. Every year, industry produces about 2.5 million tons of lead throughout the world. Most of this lead is used for batteries. The remainder is used for cable coverings, plumbing, ammunition, and fuel additives. Other uses are as paint pigments and in PVC plastics, x-ray shielding, crystal glass production, pencils, and pesticides. Target organs are the bones, brain, blood, kidneys, and thyroid gland [Joseph et al., (2010)].
Mercury
Number 3 on ASTDR's 'Top 20 List' is mercury. Mercury is generated naturally in the environment from the degassing of the earth's crust, from volcanic emissions. It exists in three forms: elemental mercury and organic and inorganic mercury. Mining operations, chloralkali plants, and paper industries are significant producers of mercury. Atmospheric mercury is dispersed across the globe by winds and returns to the earth in rainfall, accumulating in aquatic food chains and fish in lakes. Mercury compounds were added to paint as a fungicide until 1990. These compounds are now banned; however, old paint supplies and surfaces painted with these old supplies still exist. Mercury continues to be used in thermometers, thermostats, and dental amalgam. Medicines, such as mercurochrome and merthiolate, are still available. Algaecides and childhood vaccines are also potential sources. Inhalation is the most frequent cause of exposure to mercury. The organic form is readily absorbed in the gastrointestinal tract (90-100%); lesser but still significant amounts of inorganic mercury are absorbed in the gastrointestinal tract (7-15%). Target organs are the brain and kidneys [Joseph et al., (2010)].

Nickel
Electroplating is one important process involved in surface finishing and metal deposition for better life of articles and for decoration. Although several metals can be used for electroplating, nickel, copper, zinc and chromium are the most commonly used metals, the choice depending upon the specific requirement of the articles. During washing of the electroplating tanks, considerable amounts of the metal ions find their way into the effluent. Ni(II) is present in the effluents of silver refineries, electroplating, zinc base casting and storage battery etc. Higher concentration of nickel causes cancer of lungs, nose and bone., dizziness, nausea and vomiting, chest pain, tightness of the chest, dry cough and shortness of breath, rapid respiration, cyanosis and extreme weakness etc.
Chromium
Chromium is an essential element needed for human and other living organisms, which primarily involves in the action of insulin in glucose metabolism and helps transport of amino acids into the heart and liver. Its deficiency may disturb carbohydrate, lipid and protein metabolismetc. Water containing 0.5 mg/l or more chromium is considered highly toxic because it has carcinogenic and mutagenic properties. Other health problems that are caused by chromium are skin rashes, respiratory problems, weakened immune systems, kidney and liver damage, alteration of genetic material, lung cancer and death according to World Health Organization (WHO, 2007).
Zinc
Due to its remarkable resistant to atmospheric corrosion, zinc is commonly used to protect iron from rusting, in the process called galvanization. Zinc is widely used for the manufacturing of zinc white and several useful alloys such as brass, German silver, delta metal, for the preparation of gold and silver in the cyanide method, for the desilverization of lead in parks process and as an anode material in galvanic cells etc. Various zinc salts are used industrially in wood preservatives, catalysts, photographic paper, accelerators for rubber vulcanization, ceramics, textiles, fertilizers, pigments, steel production and batteries etc. [Meena et al., (2005)]. Zinc toxicity from excessive ingestion is uncommon but causes gastrointestinal distress and diarrhea.
Electroplating Industries
General
Electroplating has a long history in India; like many industrial activities, it gained momentum after Independence. Modern day electroplating started in early sixties in Mumbai with dull nickel. Bright Nickel followed soon after. Although official figures are not available, estimates indicate that in 1970, electroplating industry was considered to be in the tune of Rs. 100 million. Since then, the industry has grown steadily without facing any recession. In 1976, the first semi-automatic plant was set up in Mumbai. Currently there are more than 600 automatic plants in the country (Comprehensive Industry Document on Electroplating Industry) (COINDS), 2007.During the period 1970-85, the import restriction regulation in force led to high growth of this industry. It is estimated that electroplating industry is now worth Rs. 1000 crores (Rs.10, 000 million). This means that compounded average annual growth rate is about 16.6%. The sector employs about 1,30,000 people in approximately 12,000 organized units. The water consumption is less in electroplating industries when compared to other industries, and the effluent is more toxic than other wastes. These industries produce toxic hazardous waste containing heavy metals approximately 78,000 kg/annum which adversely effect on environment, especially on biotic components. Effluent from electroplating industry is on serious concern because just about 30-40% of the metals used during plating processes are effectively utilized i.e. plated on the articles. The remaining percentage of the metals contaminates the rinsing waters used during electroplating process. The rinse waters used during electroplating process contains about 1000 mg/L toxic heavy metals, which must be controlled to an acceptable level, in accordance to environmental regulations worldwide, before being discharged to the environment and effluents from electroplating industries is reported to contain high amounts of heavy metal ions, such as nickel, iron, lead, zinc, chromium, cadmium and copper etc. [Konstantinos et al., (2011)].These heavy metals above limits can cause adverse effect on the humans and environment.
Definition
Electroplating is one of the varieties of several techniques of metal finishing. It is a technique of deposition of a fine layer of one metal on another through electrolytic process to impart various properties and attributes, such as corrosion protection, enhanced surface hardness, lustre, color, aesthetics, value addition etc.

Fig.1.1- Electroplating effluent treatment plant
Electroplating Method
The anode and cathode in the electroplating cell are both connected to an external supply of direct current - a battery or, a rectifier. The anode is connected to the positive terminal of the supply, and the cathode (article to be plated) is connected to the negative terminal. The process of electrolysis can be explained on the basis of ionization theory. According to this theory, when the direct current is passed the electrolyte dissociates to produce positively and negatively charged ions. The positively charged (cations) ions move towards the cathode whereas negatively charged (anions) ions move towards anode. On reaching their respective electrodes, ions lose their charges and become neutral particles. The cations accept electrons from the cathode to become neutral that gets deposited in the form of metal on cathode, whereas anions gives electrons to anode to become neutral and thus forming electrolyte. The item to be coated is immersed in the bath solution as the cathode and the coating substance (the anode). However, if an inert electrode is used, the coating substance would be the metal salts in liquid form added to the solution. The metal salts subsequently dissociate into anions and cations, which then deposit onto the items to be plated.

Figure 1.2: Electroplating of a metal (Me) with copper
Electroplating process has applications in large scale manufacturing plants e.g. automobile, cycle, engineering and numerous other industries.
The basic electroplating system consists of:
1) A plating bath tilled with water containing a small amount of acid or alkali added to improve its conductivity. Thus baths used lor plating are either acid bath or alkaline bath.
2) An anode (positive electrode) - either the plating metal or an inert electrode: this is expended as the process goes on and replenished periodically
3) A cathode (negative electrode) - the item to be plated: these can he either hung inside the bath or placed in a barrel, which is rotated slowly to make the plating material deposited evenly Usually, the bath is contained in metal container, lined with acid/alkali resistant membrane e.g. pvc sheet to make it insulated trim electric circuit. The application of direct electric current across the bath solution causes the migration of
Positively charged particles (anions) towards the negative electrode (cathode) and
Negatively charged particles (cations) towards the positive electrodes (anode).
he processes are often exothermic and this leads to elevated bath temperature compared to the ambient temperature. The process efficiency depends to some degree on the.
Concentration of acid and alkali in the solution.
Temperature and.
Voltage applied across the electrodes.
The item to be coated is immersed in the bath solution as the cathode and the coating substance (the anode). However, if an inert electrode is used, the coating substance would be the metal salts in liquid form added to the solution. The metal salts subsequently dissociate into anions and cations, which then deposit onto the items to be plated. Apart from the bath chemicals and anode material, other chemical agents are used, such as brightener, wetter, booster and purifieretc.These chemical agents help to provide desired attributes, such as bright surface finish, improved and even metal deposition, depolarization, faster reaction etc. etc. The chemicals vary according to the process variants and finishing requirements for particular metal plating. By and large, most metal finishing operations typically involve 3 to 4 principal work steps or process operations, which may occur singly or in combination. These are surface preparation, pre-treatment, plating and post-treatment.
Process Chemicals
A wide variety of chemicals and substances are used, depending upon the surface properties of the objects to be electroplated, plating and finishing requirement as well as the technology / facility offered by the platters. It is very difficult to provide full details of all those used, because there are more than one commonly used process for certain metals. The general description will be covered in this section.
Solid and Hazardous Wastes
Treatment sludges contain high levels of metals, and these should normally be managed as hazardous waste or sent for metals recovery. Electrolytical methods may be used to recover metals. Sludges are usually thickened, dewatered, and stabilized using chemical agents (such as lime) before disposal, which must be in an approved and controlled landfill. The high costs of proper sludge disposal are likely to become an increasing incentive for waste minimization.
Air Emissions
A 90% recovery of the quantity of VOCs released from the process is required.
Liquid Effluents
Electroplating plants should use closed systems where feasible or attain the effluent levels presented (Sources: Pollution Prevention and Abatement Handbook, WORLD BANK GROUP Effective July 1998).
Sludges
Sludges generated from wastewater treatment. Sludges from cleaning and bath tanks and various residues like, cleaning powder. buffing compounds spent anodes and various scraps. Unused chemicals, spent resins from ion-exchange metal recovery systems also contribute to solid waste. Much of the solid waste contain hazardous and toxic substances Wherever possible, the generation of sludge should be minimized. Sludges must be dewatered and stabilized and should be disposed of in an approved, secure landfill. Leachates from stabilized sludges should not contain toxics at levels higher than those indicated for liquid effluents. Where feasible, sludges may be reused, provided that toxics are not released to the environment
'
Technologies for removal of heavy metals which are mentioned below:-
Adsorption Method
Chemical Precipitation
Membrane technology
Electro coagulation method
Ion exchange method
Coagulation method
Extraction method
Adsorption
The processes through which some of the fluid phase substances are removed by their transmission to the interface between fluid phase and a solid (separate) phase and accumulation there is called adsorption. Adsorbed material is generally classified as physisorption or chemisorption.
Physisorption or physical adsorption is a type of adsorption in which the adsorbate adheres to the surface only through Van der Waals (weak intermolecular) interactions, which are also responsible for the non-ideal behavior of real gases.
Chemisorption is a type of adsorption whereby a molecule adheres to a surface through the formation of a chemical bond, as opposed to the Van der Waals forces which cause physisorption.
Adsorption is usually described through isotherms, that is, functions which connect the amount of adsorbate on the adsorbent, with its pressure (if gas) or concentration (if liquid). One can find in literature several models describing process of adsorption, namely Freundlich isotherm, Langmuir isotherm, BET isotherm, etc.
Activated carbon produced from coconut shell (ACS) was used as adsorbent to remove Cu2+, Fe2+, Zn2+ and Pb2+ ions from electroplating industrial wastewater. The activated carbon produced was chemically activated with zinc chloride [Bernard et al., (2013)].
Chemical precipitation
Chemical precipitation is a method of wastewater treatment. Wastewater treatment chemicals are added to form particles which settle and remove contaminants. The treated water is then decanted and appropriately disposed of or reused. The resultant sludge can be dewatered to reduce volume and must be appropriately disposed of. Chemical precipitation can be used to remove metals, fats, oils and greases (FOG), suspended solids and some organics. It can also to be used to remove phosphorus, fluoride, ferrocyanide and other inorganics. It can be used on a small or large scale. A beaker full of waste, a 50,000 tank, a 1,000,000 gallon lagoon or a lake can be batch treated with chemicals. Chemical precipitation can be used in a continuous treatment system on flows ranging from a trickle to 1 gallon/minute, 1,000 gallons/minute and more. Chemical precipitation can be accomplished with very little equipment. For example, a 55 gallon drum and a mixing paddle can be used by a small discharger to treat wastewater with little capital investment. For larger volumes, a tank with a mixer and chemical feed pumps will suffice. For even larger volumes a continuous system with metering pumps, mixing tanks, a clarifier and control instrumentation can be employed. Metal precipitation is primarily dependent upon two factors: the concentration of the metal, and the pH of the water. Heavy metals are usually present in wastewaters in dilute quantities (1-100 mg/l) and at neutral or acidic pH values (pH<7.0) [Brboot et al., (2011)].
Membrane Technology
The membrane processes can be classified according to the size range of the separated species:
Reverse osmosis is used to separate dissolved salts and small organics (size under 1 nm). Example: production of drinking water from seawater or seawater desalination.
Nan filtrationis used to separate antibiotics (size under 10 nm). Example: selective demineralization of water or concentration of organic solutions.
Ultra filtrations used to separate emulsions, colloids, macromolecules or proteins (size under 100 nm).Example: treatment of pulp and paper industry's effluentsmicro-filtration is used to separate small particles, large colloids and microbial cells (size under 10 mm). Example: removal of microorganisms from the fermentation products.
Gas and vapor separation is used to isolate a gas from a mixture of gases or vapors. Example: recovery of ammonia or hydrogen from industrial gases.
Electrodialysis used to separate anions and cations by means of two charged membranes (anode and cathode). Example: production of pure water.
Membrane technology was one option for a nonpolluting process. The membrane of optimum pore sizes was capable of removing almost all pollutants without using any chemicals. Sludge obtained in the process contained only pollutant constituents in this feed stream. In order to increase the removal efficiency and reduce the operating cost, membrane technology was also used together with other treatment processes. The concentrations of heavy metals in permeate varied with feed pressure. At high pressure, the particles blocked in the pore were pushed away and discharged with the permeate. For longer time of filtration, more particles will be pushed away with the permeate. Smaller pore size membrane may be another alternative for high rejection but require a high pressure unit for operation that lead to high cost and the difficulty in controlling the process at high pressure. If the floc sizes increase by mean of good pretreatment of the wastewater operating at low pressure, lower cost and prolonged membrane life will be well achieved [Srisuwanet al., (2002)].
Electocoagulation method
Electro'coagulation is a technology that has been known for more than one hundred years. However, no systematic research has been developed that can be used to predict its chemical behavior, reactions and mechanisms, or can provide sufficient tools for the design and operation of the reactors. The technique relies on the electrochemical dissolution of sacrificial Al or Fe electrodes. The generated cations contribute by diminishing the stability of the suspended entities, by decreasing their zeta potential. Also, upon formation of hydroxide ions at the cathode, metal ions complex with iron or aluminum hydroxides, which are known to be efficient coagulants. The pollutants from many different effluents are removed by applying the principle of coagulation; however, in electro'coagulation, no use is made of a chemical coagulant. Electro'coagulation can be defined as a process in which the suspended pollutants are destabilized, emulsified or dissolved in an aqueous medium, by inducing electrical current in the water through parallel metal plates of different materials, iron and aluminum being the most commonly used. The process has been used for removal of contaminants from different wastewaters. One of the best known and most popular applications of electro'coagulation has been the treatment of wastewater from the electroplating and metal plating industries, a process that strives to remove the bulk of the soluble metals in the discharge [Sicairos al., (2011)].

Ion Exchange Method
Ion exchange can be used for the removal of undesirable anions and cations from a wastewater. Cations are exchanged for hydrogen or sodium and anions for hydroxyl ions. Ion exchange resins consist of an organic or inorganic network structure with attached functional groups. Most ion exchange resins used in wastewater treatment are synthetic resins made by the polymerization of organic compounds into a porous three-dimensional structure. Ion exchange resins are called cationic if they exchange positive ions and anionic if they exchange negative ions. Cation exchange resins are comprised of acidic functional groups, such as sulphonic groups, whereas anion exchange resins have basic functional groups, such as amine. The strength of the acidic or basic character depends upon the degree of ionization of the functional groups, similar to the situation with soluble acids or bases. Thus, a resin having sulphonic acid groups would act as a strong acid cation exchange resin. Ion exchange has a great potential to remove heavy metals from industrial wastewaters or heavy metal-containing sludge. In order to design and operate heavy metal removal processes, the equilibrium relationship between ions and resin must be known a prior. [Lee et al.,(2007)].
Coagulation method
Coagulation is the process in which particles in water are clumped together into larger particles, called floc. In a well-run water treatment plant, adjustments are often necessary in order to maximize the coagulation/flocculation process. These adjustments are a reaction to changes in the raw water entering the plant. Coagulation will be affected by changes in the water's pH, salt content, alkalinity, turbidity, and temperature.
Within the plant, two more factors can influence coagulation. Mixing effects and coagulant effects will both influence the coagulation/flocculation process. Coagulation is a unit process used for removing colloids and other suspended particles from water and wastewater. It may be employed as source treatment for the removal of contaminants such as metals, within the treatment train, or with filtration as a polishing step. Coagulation destabilizes colloidal particles by charge neutralization and promoting collisions between neutralized particles. This study to examine the effectiveness of polymer addition to coagulation process during treatment of a beverage industrial wastewater to remove some of its trace metals content such as lead, cadmium, total iron, total chromium, nickel and zinc [Amudaet al (2006)].

Extraction
Solvent extraction is a method for separating a substance from one or more others by using a solvent. It relies on variations in the solubilities of different compounds in different substances. In most cases, the substance to be extracted, which may be a solid, a liquid or a gas, is dissolved in a liquid, along with other substances, and a liquid solvent is used for the extraction ' this is sometimes called liquid-liquid extraction. The technique may also be applied to solid materials that contain compounds that need to be extracted. This method is widely used in industry, and in the laboratory for refining, isolating and purifying a variety of useful compounds Solvent extraction is now a very well-established process in hydrometallurgy. It is used for the hydrometallurgical processing of copper, nickel, cobalt, zinc, uranium, molybdenum, tungsten, vanadium, rare earths, zirconium, hafnium, niobium, tantalum, indium, gallium, germanium, the platinum group metals, boron, reprocessing nuclear fuels, purification of wet process phosphoric acid, nitric acid recovery, etc. [Silva et al., (2005)]

Selection of Process
Various chemical and physical methods have been used to remove heavy metals from waste water in the last few decades. Their advantages and limitations in application are evaluated. To highlight their removal performance, the main operating conditions such as pH and treatment efficiency are presented as well. These methods include chemical precipitation, solvent extraction, ion exchange, evaporation, reverse osmosis, electrolysis and adsorption.
From these methods, chemical precipitation, solvent extraction, ion exchange and adsorption are more commonly used which are mentioned below:-
Chemical precipitation has traditionally been used to remove heavy metal ions from wastewater with relatively high concentrations. The operation of chemical precipitation is simple but generates large quantity of sludge that is often difficult for further disposal. In addition, chemical precipitation is usually not effective to remove trace levels of metal ions from aqueous solutions.
Solvent extraction has widely been used in organ metal removal. Although the process may have fast kinetics and high capacity, solvent extraction is often costly due to the quantity and specific type of solvents needed.
Ion exchange method has commonly been used to remove metal ions from water or wastewater, but the process has slow kinetics, consumes additional chemicals, generates hazardous streams, and is not well applied to heavy metal ions due to possible problem of resin pollution.
Adsorption has been considered as, possibly, the most cost-effective method for heavy metal ion removal, especially at medium to low concentrations, because the process is simple, and chemical consumption or waste generation is not a significant issue. However, traditional adsorbents, such as activated carbon, are often not effective to adsorb heavy metal ions from water or wastewater.


Adsorption
History
Adsorption has been used for centuries. It is thought that the idea was first conceived in ancient times. However, first results or observations weren't documented until the late 1700's. At that time, adsorption was used to test the ability of charcoals and clays to uptake gases. With more research, by 1814 it was concluded by de Saussure, that all types of gases can be taken up by porous substances such as asbestos, cork, sea-foam, in addition to charcoal. By the early 1900's, the Freundlich equation was developed but was not theoretically justified. The adsorption isotherm is known as Freundlich equation, due to Freundlich's emphasis on the importance of the equation, which developed its extended use, although it was believed the equation was developed in the empirical form a decade earlier by Boedecker. Other equations were also developed and included Langmuir, Euckena, and Polanyi. Langmuir's equation was originally developed for monolayer adsorption. It is this equation that is considered as the practical equation that corresponding to an ideal and localized monolayer. Branauer, Emmett, and Teller (BET) proposed the multilayer isotherm. The BET equation uses the same assumptions as Langmuir, and assumes that Langmuir's equation applies to every adsorption layer. It was the BET theory that was the initial endeavor at creating a universal theory of physical attraction. The Langmuir and BET theories and equations are the most widely used equations for monolayer and multilayer adsorption.Adsorption is an effective purification and separation technique used in industry especially in water and wastewater treatments. A number of methods for toxic metal removal from waste water have been used, but most have several disadvantages, such as continuous input of chemicals, high cost, toxic sludge generation or incomplete metal removal but the adsorption process has been found advantageous such as: low cost of adsorbent, easy availability, utilization of industrial, biological and domestic waste as adsorbents, low operational cost, ease of operation compared to other processes, reuse of adsorbent after regeneration, capacity of removing heavy metal ions over wide range of pH and to a much lower level, ability to remove complex form of metals that is generally not possible by other methods, environmentally friendly, cost effective and technically feasible.Adsorption process is the best process for removal of metals from wastewater because it is simple, time saving and inexpensive.

2. LITERATURE REVIEW
Dutta et al., (2014) was studied on the adsorption of Cu(II) ions from electroplating industrial wastewater by using microwave assisted activated carbon. The effects of different experim ental parameters on Cu(II) adsorption were investigated. Parameters like heavy metal concentration, adsorbent dose, contact time and agitation speed have studied. It was found that 99.9 % of Cu(II) removal efficiency and 98.63% of COD removal efficiency was achieved within first 80 min of the batch adsorption study with an initial concentration of 100 mg/L, adsorbent concentration of 1 g/L, pH of 6, temperature of 30 ??C, particle size of 105 ??m and agitation speed of 200 rpm. The kinetics of the adsorption follows the pseudo second order rate kinetics. After series of batch studies it was found that the residual Cu(II) concentrations were below the WHO prescribed limit of 1.5 mg/L.
Cassava peel, the agro-waste produced from starch or the bioethanol industry, can be used as a biosorbent for the removal of heavy metals from wastewater by Phaisanthia in the year of 2013. The advantages of cassava waste are low-cost and high efficiency for heavy metals removal. However, its capability to treat real wastewater loaded with multi-heavy metals such as nickel, chromium, and copper has never been reported. The main objective of this research was to investigate the optimum factors of heavy metals removal from real electroplating wastewater using cassava peel waste. Adsorption experiments of Ni, Cu and Cr onto cassava peel waste were performed by studying some parameters including contact time, initial pH, and dose of adsorbent. In addition, two difference isotherm models including Langmuirand Freundlich were used to investigate the adsorption process. The results showed the adsorption time reached equilibrium at 300 min. Heavy metals removal efficiency of heavy metals depended on initial pH of wastewater. The result showed that pH 4 was the optimum initial pH for adsorption of Ni and Cu while pH 2 was best for the removal efficiency of chromium for cassava peel waste. The highest removal efficiency of nickel and copper using cassava peel waste was 93% and 99 %at pH 2, respectively, while chromium was 88% at pH 4. Equilibrium modeling of the adsorption isotherm showed that adsorption of three heavy metals on cassava peel waste could be described by Langmuir and Freundlich model. Furthermore, the result of the adsorption isotherm demonstrated that the ability of heavy metal removal (Kf) was in the following order; nickel > chromium > copper at pH 4, respectively. The maximum adsorption capacities for Ni and Cu were 4.33 and 0.23 mg/g at pH 4, respectively. The maximum capacity of chromium was 0.59 mg/g at pH 2.
Removal of lead (Pb) and cadmium (Cd) ions by modified shrub calotropisprocera roots materials from synthetic solution was investigated by Jothi in the year of 2013. The adsorption was found to be drastically depending on initial metal ion concentration, adsorption dosage, contact time and agitation speed. Further more the equilibrium data of adsorption are in good agreement with the models of Freundlich and Langumir. Solution containing the 1000 mg/l concentration of lead and cadmium were prepared by dissolving lead nitrate, and cadmium chloride. The percentage of Pb ion removal due to bioadsorption was calaculated as % Pb as removal =[Co- Ci/Co] x 100 %, where Ci and Co are the initial and final concentration of Pb (II) solution ( mg/L) respectively and the percentage of Cd ion removed due to bioadsorption was calculated as % Cd as removal =[Co-Ci/Co] x 100 %, where Ci and Co are the initial and final concentration of Cd (II) solution( mg/L) respectively.
In the year of 2013 by Parmar was worked on removal of cadmium from aqueous solution using cobalt silicate precipitation tube (CoSPT) as adsorbent. 50 ml of cadmium solution of desired strength (initial concentration, C0), pH and a known weight (m) of the powdered CoSPT were taken in a stoppered conical flask and shaken in a horizontal shaker for adsorb ate-adsorbent contact. Cobalt silicate precipitation tube (CoSPT), prepared through 'silica garden' route was found to be potential adsorbent for removal of cadmium from aqueous medium. Detail adsorption study of Cd(II) on CoSPT was investigated. Batch adsorption studies were carried out as a function of contact time, adsorbent dose, adsorbate concentration (50-300 mg L-1), temperature (298-323K). Cd(II) loading on CoSPT was dependent on initial Cd(II) concentration. Experimental adsorption data were modeled using Freundlich and Langmuir isotherm equations. pH variation study revealed that the adsorption increased with increase in pH of the solution. Cd(II) loading capacity of CoSPT was estimated at 319 mg g-1, which ranks high amongst efficient Cd(II) adsorbents. Adsorption data were analyzed using two kinetic models, Lagergren first order and pseudo second order. It was observed that pseudo second order rate equation represented the best correlation.
Goswami et al., (2013) was reported that fly ash as an adsorbent for removal of copper ions from synthetic wastewater. Batch experiments were carried out to investigate the effect of contact time, adsorbent dosage, and temperature. The values of optimum parameters were found. The optimum time is between 40 to 60 minutes. The adsorbent dose of 2 g/l was found to be optimum. The equilibrium adsorption data were fitted to Langmuir and Freundlichadsorption isotherm models and model parameters were evaluated. The results show that Fly ash can be employed as it is (after physical activation) to use it as low cost adsorbent for adsorption of Cu (II) from aqueous solution.
Investigated was done by Venkatesan in the year of 2013 that the removal of cadmium using wood of derris indica based activated carbon. Its adsorption capability in removal of cadmium from wastewater has been observed through batch adsorption experiments. The adsorption kinetics of this carbon for various parameters like adsorbent dosage and contact time of the cadmium ion were studied. The cadmium adsorption behavior and the effect of the initial cadmium concentration on removal efficiency were also examined. The optimum dosage of wood of derris indica based activated carbon to remove 80 mg/L of cadmium from aqueous solution 0.5gms/150 mL and the optimum contact time was 20 minutes. It was studied that up to a carbon concentration of 0.4 gm/150 ml the removal of cadmium is varying and at 0.5 g/150 ml of carbon concentration the cadmium ion removal was significant around 87.50% and from there onwards the percentage of cadmium ion removal is slightly varying and equilibrium is almost achieved at 0.5 g/150ml at a optimum time of 20 minutes. The isotherm data confirm with both Langmuir and Freundlich isotherm models.
Ossman was observed that the removal of Cd(II) ion from wastewater by adsorption onto treated old newspaper in the year of 2013. The results indicated that the adsorption of Cd(II) increased with the increasing pH, and the optimum solution pH for the adsorption of Cd(II) was found to be 6.4. Adsorption was rapid and occurred within 15 min for Cd(II) concentration range from 5 to 30 mg/L. The kinetic process of Cd(II) adsorption onto TNP was found to fit the pseudo-second-order model. The equilibrium adsorption data for Cd(II) were better fitted to the Langmuir adsorption isotherm model.
Hegazi (2013), worked on removal of heavy metals like Cu, Ni, Fe etc. from electroplating industrial wastewater by using rise husk and fly ash as adsorbents. The objective of this research is to study the utilization possibilities of less expensive adsorbents for the elimination of heavy metals from wastewater. In general the sorption consisted of 20 mg/l for the adsorbent dose in 10 mg/l of concentration metal (Cu, Ni, Fe) at an agitation rate of 200 rpm with an adsorbent time of 20 min at room temperature(25?? 3). Results showed that low cost adsorbents can be fruitfully used for the removal of heavy metals with a concentration range of 20'60 mg/l.
Production and experimental efficiency of activated carbon from local waste bamboo from wastewater was investigated by Awoyale in the year of 2013. The removal of heavy metal ions was pH dependent as the concentration of both metals after adsorption at the maximum pH of 8 was recorded to be <0.001 mg/l implying that adsorption capacity increases with increasing the pH value of the solution, and at a particular pH. The order of increase of removal percentage was Pb > Cu for both absorbents. Results showed that the best pH for adsorption was 8 with contact time of 120 minutes. When the addition of the adsorbent dose increased, the percentage removal of metal ions also increased. A maximum removal of approximately 100% was due to the assumption of approximately 0 mg/l concentration of the metals at pH 8 and dosage of 44. This was observed for both metal ions for 4g dosage. This investigation also showed that absorbent produced from bamboo is suitable for removing the Pb and Cu heavy metal ions in a typical refinery wastewater scheme. Other metal ions may be effectively removed. This is however open for further studies. For comparative study, steam activation and thermal activation should be carried out on Nigerian bamboo. Effect of various activating agents such as acetic acid, and sulphuric acid, hydrochloric acid etc and, alkaline based activating agents on the textural properties of activated carbon from Nigerian bamboo should be researched upon. The condensate obtained during the pyrolysis could be refined to yield 70% of diesel. Therefore further analysis should also be conducted.
Removal of cadmium from aqueous solution by modified low cost adsorbent in the year of 2013 was studied by Ingole. The main categories of adsorbents are carbon, agricultural wastes, industrial wastes, low grade ores, clays and lowcost synthetic oxides/hydroxides such as iron/manganese/ aluminum. Literature showed that pH is an important factor that could make a major change in the adsorption capacity. The various adsorption parameters studied to evaluate their effectson Cd(II) removal efficiency are: contact time, pH, temperature, adsorbate and adsorbent concentrations. It is evident that low-cost adsorbents have demonstrated outstanding removal capabilities for certain metal ions as compared to activated carbon. In this review, an extensive list of agricultural wastes as adsorbents including rice husk, sawdust (cedrusdeodhar wood), sawdust (Pinussylvestris), walnut sawdust, juniper fibre, sugarcane bagasse, wheat bran, cassava, tuber bark waste, cassava waste, corncorb, coir pith, and others has been compiled. Chemically modified agricultural wastes exhibit higher adsorption capacities than unmodified forms.
Ahlam et al., (2012), worked on the biosorption of Zn(II), Ni(II), Cu(II) and Cd(II) ions from aqueous solutions onto ceratoniasiliqua (Carob tree) bark has been investigated in a batch biosorption process. The biosorption process was found to be dependent on pH of solution, initial metal ion concentration, biosorbent dose, contact time and temperature. The experimental equilibrium biosorption data were analyzed by Langmuir, Freundlich, Temkin and Dubinin-Radushkevic isotherm models. The Langmuir model gave a better fit than the other three models by higher correlation coefficient, R2. The maximum biosorption capacity calculated from the Langmuir isotherm was 42.19 mg/g, 31.35 mg/g, 21.65 mg/g and 14.27 mg/g for Ni(II), Zn(II), Cu(II) and Cd(II), respectively at optimum conditions. The kinetic studies indicated that the biosorption process of the metal ions followed well pseudo-second-order model. The negative values of ??Go and the positive ??Ho revealed that the biosorption process was spontaneous and endothermic. According to the biosorption capacity, Ceratoniasiliquabark considered as an effective, low cost, and environmentally friendly biosorbent for the removal of metal ions ions from aqueous solutions.
Removal of copper from industrial wastewater by using adathodavasicas tem as low cost adsorbent was worked in the year of 2012 by Ahamed. It was used as adsorbent to remove Cu2+ from an industrial wastewater. For this purpose, high grade CuSO4.5H2O was used as heavy metal sample. Laboratory experimental investigation was carried out to identify the effect of pH (1.50 ' 5.5), agitation time (30-240 min) varying temperature (30-50??C) and varying biomass quantities (2,4,6,8,10 g/L) and other co-existing ions were also examined. The kinetics of interactions weretested with pseudo first order Lagergren equation and first order reversible 'Bhattacharya Venkobachar equation. The Langmuir & Freundlich adsorption isotherm models fitted the experimental data best with regression coefficient r2> 0.95 for the Cu(II) ions. The adsorption was endothermic and the computation of the parameters ??G??, ??H?? & ??S?? indicated that the interactions were thermodynamically favorable. The results showed that adathodavasicastem carbon (AVSC) was an effective & economical biosorbent material for the removal and recovery of heavy metal ions from waste water.
Muhammad et al., (2012) was investigated that the removal of cadmium, chromium and lead from industrial wastewater by using algae-seaweed (Ascophyllumnodosum) as adsorbent at two temperatures (23.5??C and 37??C) and four pH values (2, 5, 7 and 10). Atomic absorption spectroscopy (AAS) adsorption results show maximum adsorption capacities of 93.41% for lead at pH 2, 53.13% for cadmium at pH 10 and no adsorption for chromium throughout the pH range and temperature were found to have no significant effect on the adsorption process, especially for cadmium and lead. However, the effect of pH was significant and varied with each metal. These results were found to be comparable to results reported from previous works. The results show that the removal efficiency of each adsorbent is highly dependent on pH, and metal ion removal occurred in the preferential order lead > cadmium > chromium, depicting strong contributions from the ionic radius of each metal ion. These results demonstrate the immense potential of the adsorbent as alternatives for metal removal from industrial effluent treatment.
Abbas et al., (2012) was studied that the adsorption of lead ions from solutions containing different initial lead concentrations (100, 150 and 200 ppm pb as lead nitrate) using different particle size (140, 300 and 500 ??m) and different doses of activated carbon, sand and egg shells at different pH (4, 7 and 10) was examined. Also the metal concentration retained in the adsorbent phase (mg/g) was calculated. This method of heavy metals removal proved highly effective as removal efficiency increased with increasing adsorbent dose while it decreased with increasing metals concentration. The results revealed that of the studied adsorbents, the activated carbon showed the highest adsorption capacity and the maximum adsorption can be obtained by using particle size of 140 ??m in neutral media (pH 7). This technique might be successfully used for the removal of lead ions from liquid industrial wastes and wastewater.
Sorption study of Co (II), Cu(II) and Pb(II) ions removal from aqueous solution by adsorption on flamboyant flower (Delonix Regia) was researched by Jimoh in the year of 2012. The ability of Delonixregia (Flamboyant) flower to remove Co(II), Cu(II) and Pb(II) ions from aqueous solutions through bio-sorption was investigated in multi metal batch experiments at 32??C. The metal ions concentration was determined by atomic absorption spectroscopic (AAS) method. The influence of pH, contact time, adsorbent dosage and initial metal ion concentration were investigated. The study revealed that maximum removal of Co(II), Cu(II) Pb(II) ion from aqueous solution occurred at pH of 5. The contact time for the adsorption process was found to be at 60 minutes. The amount of metal ions adsorbed increases with increase in adsorbent dosage and initial metal ion concentration. The bio-sorption of Pb(II) and Co(II) ions exhibited pseudo-second-order kinetics models whereas Cu(II) ion followed for both pseudo first order and second order kinetics model. This study shows that Delonixregiaflower is a viable agricultural waste for the removal of Co(II), Pb(II) and Cu(II) ions from aqueous solution.
Okafor et al., (2012) was studied thatthe adsorption capacity of coconut (Cocosnucifera L.) shell for Pb2+, Cu2+, Cd2+ and As3+ from aqueous solutions. The effect of various operational parameters such as concentration, pH, temperature and sorption time on the adsorption of Pb2+, Cu2+, Cd2+ and As3+ was investigated using batch process experiments. It was found that coconut shell (CNS) can be used as a low cost adsorbent for the removal of heavy metals in aqueous solution containing low concentrations of the metals. The maximum ion adsorption capacities followed the trend Pb2+>Cu2+>Cd2+>As3+ and the percentage adsorption was found to depend on the concentration of the adsorbent present, the solution pH, temperature and the sorption. The average values of the activation energy of adsorption for coconut shell (CNS) were 7.99, 3.79, 10.24 and 53.977KJ/mol for Pb, Cu, Cd and As respectively. This shows that the adsorption of metal ions on the adsorbent is physical adsorption mechanism. Kinetic treatment of the results gave a pseudo-second order type of mechanism while the adsorption characteristics of the adsorbent followed the Freundlich adsorption isotherm.
Sheng-Fong Lo et al., (2012), worked on adsorption capacity and removal efficiency of heavy metal ions by Moso and Ma bamboo activated carbons, the carbon yield, specific surface area, micropore area, zeta potential, effects of pH value, soaking time and dosage of bamboo activated carbon were investigated. In comparison with onceactivatedbamboo carbons, lower carbon yields, larger specific surface area and micropore volume were found for thetwice-activated bamboo carbons. The optimum pH values for adsorption capacity and removal efficiency of heavymetal ions were 5.81'7.86 and 7.10'9.82 by Moso and Ma bamboo activated carbons, respectively. The optimum soaking time was 2'4 h for Pb2+, 4'8 h for Cu2+ and Cd2+, and 4 h for Cr3 by Moso bamboo activated carbons, and 1hfor the tested heavy metal ions by Ma bamboo activated carbons. The adsorption capacity and removal efficiencyof heavy metal ions of the various bamboo activated carbons decreased in the order: twice-activated Ma bamboocarbons > once-activated Ma bamboo carbons > twice-activated Moso bamboo carbons > once-activated Moso bamboo carbons. The Ma bamboo activated carbons had a lower zeta potential and effectively attracted positively chargedmetal ions. The removal efficiency of heavy metal ions by the various bamboo activated carbons decreased in the order: Pb2+> Cu2+> Cr3+> Cd2+.

Removal of lead and cadmium ions from aqueous solutions by using manganoxide mineral as adsorbent was investigated by Sonmezay in the year of 2012. The kinetics of adsorption process data was examined using the pseudo-first-order, pseudo-second-order kinetics and the intra-particle diffusion models. The rate constants of adsorption for all these kinetics models were calculated and compared. The adsorption kinetics was best described by the pseudo second-order model. The Langmuir and Freundlich adsorption isotherm models were applied to the experimental equilibrium data at different temperatures. 50 mL solution at desired concentrations which were 250 and 50 mg/L for lead and cadmium, respectively. The experimental data well fitted to Langmuir isotherm model. The maximum adsorption capacities of manganoxide mineral for lead and cadmium ions were calculated from the Langmuir isotherm and were 98 and 6.8 mg/g, respectively.
Imtiaz was studied that the synthesis of metal oxide and its application as adsorbent for treatment of wastewater effluent in the year of 2011. The method is preferred over the others for being simple and efficient giving a percentage yield of 80% and 63% for the synthesized Fe and Ni particles, respectively. The particle size ranges in diameter ~10-20nm and 40nm for iron and nickel particles, respectively. A composite of Fe and Ni in 1:1 molar ratio was also prepared by thorough mechanical grinding in agate pestle and mortar till fine, uniform, and blended powder. The characterization of synthesized materials confirmed the linkage of metal-oxygen and red shift through FTIR and UV-Visible spectroscopic technique, respectively. Sampling was done for three categories of water samples; industrial (five different industries), municipal and drinking water samples. Composite aqueous sample of each category was characterized for its physicochemical parameters like pH, EC, COD, and concentration of nitrates, sulphates, nickel, copper, cadmium and lead. The analysis presents the effluent sample of leather industry exceeding the permissible limits significantly higher for nitrates, nickel, lead, and cadmium as compared to other effluents. Whereas municipal wastewater samples depicted exceeding limits for Cu, Ni, Pb and Cd concentration. The synthesized metal particles were applied as adsorbents for the removal of different pollutants in batch experiments. The optimum removal efficiency of 97%, 96% and 98% for lead was achieved by Ni, Fe and composite particles, respectively. On comparison of efficiency of different adsorbents, Iron particles showed remarkably good efficacy for removal of metals in terms of attaining equilibrium in relatively short time (15 minutes). However, pollutants like sulphates and nitrates were more effectively reduced by Ni particles to 18 and 54 times less than the background concentration. Adsorption Kinetics and Equilibrium models were applied. The kinetics revealed pseudo second order relatively more fitted than pseudo first order. On the other hand, equilibrium models of Langmuir and Freundlich gave comparable fitness to adsorption data with coefficient of regression 0.999.
Ideriah et al., (2011), worked on removal of Pb, Cu, Ni and Cr from aqueous solution by using palms fruit fiber in removing as adsorbent. On fond that it is the function of concentration, contact time and pH variations. Palm fruit fiber from the study locations were washed with deionized water, air-dried and ground using electric grinder. The powdered fiber was sieved and treated with 0.3 M HNO3 solution for 24 h, washed with deionized water until pH 7.2 and oven dried at 60??C. The biomass was added to 1M stock metal ion solutions made from Copper sulphate, potassium dichromate, lead nitrate and nickel sulphate. The concentrations, contact time and pH of each stock solution were varied. The mixtures were shaken, filtered and analyzed by GBC avanta atomic absorption spectrophotometer version 2.02. The results showed mean percentage recovery of 51.08% Pb, 54.75% Cu, 46.96% Ni and 44.91% Cr for concentrations, 96.96% Pb, 9.79% Cu, 49.21% Ni, and 7.63% Cr with contact time, 60 ' 80 minand 87.48% Pb, 82.86% Cu, 56.71% Ni and 37.68% Cr with pH, 2 ' 4. The application of the biomass to waste water showed percentage removal of 73% Pb, 78% Cr, 82% Cu and 87% Ni. The mean percentage removal value revealed Pb as the highest and Cr as the least adsorbed. The sorption capacity of the biomass decreased with increasing concentration of metal ion but increased with decreasing pH and increasing contact time. Chemical modification of the biomass enhanced its capacity. Thus the palm fruit fiber biomass is cost effective and has great potential for use as adsorbent in removing heavy metals from aqueous solutions.
Biosorption of cadmium (Cd (II)) and arsenic (As(III)) ions from aqueous solution by tea waste biomass also a batch experimental setup was studied Kamsonlian in the year of 2011 . The effects of pH and temperature on the biosorption were studied in this work. The optimum pH for the maximum efficiency of biosorption of Cd (II) and As (III) were found to be 5.5 and 7.5, respectively. The adsorption process was endothermic in nature and spontaneous. About 95 and 84.5% removal of Cd (II) and As (III) ions was obtained at 200 mg/l of adsorbate and 6 g/l and 7 g/l of adsorbent dosage, respectively. The present study showed that tea waste biomass can serve as a good and cheap substitute for conventional carbon- based adsorbents.
Onundi was observed that the adsorption of copper, nickel and lead ions from synthetic semiconductor industrial wastewater by using palm shell activated carbon as adsorbent. In the year of 2011. Laboratory experimental investigation was carried out to identify the effect of pH and contact time on adsorption of lead, copper and nickel from the mixed metals solution. Equilibrium adsorption experiments at ambient room temperature were carried out and fitted to Langmuir and Freundlich models. Results showed that pH 5 was the most suitable, while the maximum adsorbent capacity was at a dosage of 1 g/L, recording a sorption capacity of 1.337 mg/g for lead, 1.581 mg/g for copper and 0.130 mg/g for nickel. The percentage metal removal approached equilibrium within 30 min for lead, 75 min for copper and nickel, with lead recording 100 %, copper 97 % and nickel 55 % removal, having a trend of Pb2+> Cu2+> Ni2+. Langmuir model had higher R2 values of 0.977, 0.817 and 0.978 for copper, nickel and lead respectively, which fitted the equilibrium adsorption process more than Freundlich model for the three metals.
Samorn et al., (2011), worked on the adsorption capacity of activated carbons synthesized from bamboo waste using KOH activation have greater specific surface areas (1281.7-1532.8 m2/g) and pore volumes (0.4246-0.4911 cm3/g) than a commercial activated carbon. They have iodine numbers between 811.2 and 850.4 mg/g which are greater than the standard value specified by Thai Industrial Standards Institute, implying a potential to be developed to a commercial scale. Increasing carbonization time improves the specific surface area, pore volume and iodine adsorption capacity of bamboo-derived activated carbon. Lower adsorption capacity for methylene blue compared to iodine indicates microporous structure of the activated carbons. In water treatment, the synthesized activated carbons can reduce COD, TDS, turbidity and UV254 significantly. The synthesized activated carbons have removal efficiencies comparable to the commercial activated carbon regarding to COD, TDS and turbidity.
At least 20 metals which cannot be degraded or destroyed. The important toxic metals are Cd, Zn, Pb, Cr, Cu, and Ni. Effect of pH has studied by various authors in the range of 1-12 and optimum was found in the range of 4-6 by Wasewar in the year of 2010. Effect of adsorbent dose have studied in the range of 0.2 gm/lit to 20 gm/lit. Optimum dose was varied as the studied range was varied. For pseudo-second order kinetics, the value of ksmodel parameter have found in the range of 0.0091 ' 0.1664 g/mg min and the value of initial sorption rate was observed in the range of 2 ' 26.5 mg/g min. Intra-particle diffusion model have used to present the kinetic data for the removal of zinc by adsorption onto TFW. Model parameters were found in the range of 0.0072 - 1.456 mg/g min. The negative values of free energy at all temperatures studied have been observed which is due to the fact that adsorption process is spontaneous. The positive value of free energy suggests increased randomness at the solid/solution interface during the adsorption of metal ions onto adsorbent.
Moreno et al., (2010), was studied that the removal of Mn, Fe, Ni and Cu ions from industrial wastewater by using cow bone charcoal as adsorbent. CBC has the ability to retain Mn2+, Fe2+, Ni2+and Cu2+ metals ions from aqueous solutions at the studied concentrations. Removal of heavy metals (manganese, iron, nickel and copper) from aqueous solution was possible using a activated carbon obtained from cow bone charcoal (CBC). It was seen that adsorption took place for the four metals within 25 minutes for the concentration levels studied. Under our experimental conditions and for the studied heavy metals pH plays an important role in the adsorption process, particularly on the adsorption capacity. The pH selected for an optimal rate of adsorption for all ions investigated is 5.1. It is shown that CBC has a relatively high adsorption capacity for these heavy metals; the quantities adsorbed per gram of CBC at equilibrium (qe) are 29.56 mg'g'1 for Mn2+, 31.43 mg'g'1 for Fe2+, 32.54 mg'g'1 forNi2+ and 35.44 mg'g'1 for Cu2+. This adsorption is described by an isotherm of type I and is fully matched by the Langmuir isotherm. The kinetics of the manganese, iron, nickel and copper adsorption on the CBC was found to follow a pseudo-second-order rate equation. This method has an additional advantage, as it could be applied in developing countries due to the low cost.
Removal of Cd, As, Hg, Co and Cu from industrial wastewater by using bacteria was reported by Nanda in the year of 2010. From this study five effluent samples out of nine were selected to study the removal of heavy metals by bacteria. After treatment it was found that Pseudomonas sp. and Bacillus sp. were able to remove Cd from the effluent samples with an average reduction of 56% and 44% respectively. Removal of as was recorded by Pseudomonas sp. with an average reduction recorded of 34%.Hg was removed by Bacillus sp. with an average reduction of 45%. Cu was removed by both Bacillus spandStaphylococcus sp. with an average reduction recorded of 62% and 34% respectively. Co was removed by Pseudomonas sp. and the average reduction recorded was 53%.
Slaiman et al., (2010), worked on biosorbent of England bamboo plant origin for removal of priority metal ions such as Cu and Zn from aqueous solutions in single metal state. Batch single metal state experiments were performed to determine the effect of dosage (0.5, 1 and 1.5 g), pH (3, 4, 4.5, 5 and 6), mixing speed (90, 111, 131, 156 and 170 rpm), temperature (20, 25, 30 and 35 ??C) and metal ion concentration (10, 50, 70, 90 and 100 mg/L) on the ability of dried biomass to remove metal from solutions which were investigated. Dried powder of bamboo removed (for single metal state) about 74 % Cu and 69% Zn and maximum uptake of Cu and Zn was 7.39 mg/g and 6.96 mg/g respectively, from 100 mg/L of synthetic metal solution in 120 min. of contact time at pH 4.5 and 25??C with continuous stirring at 170 rpm. Experimental results have been analyzed using Langmuir and Freundlich isotherms. Both equilibrium sorption isotherms were found to represent well the measured sorption data, but Freundlich isotherm was better than Langmuir isotherm. The effect of time was studied and the rate of removal of Cu (II) and Zn (II) ions from aqueous solution by bamboo plant was found. The rates of sorption of copper and zinc were rapid initially within 5-15 minutes and reached a maximum in about 60 minutes.
Adsorption of Cd and Pb ions from aqueous solution by using low cost adsorbent was done by Hayder in the year of 2009. Initial concentration of 1000 mg/l by the dissolving 2.75 gm of Pb(NO3)2.4H2O in 2.5 l of distilled water and 1.82 gm of Cd(NO3)2.2H2O in 2.2 l distilled water. The results showed that maximum adsorption capacity occurred at 486.9??10-3 mg/kg for Pb2+ ion and 548.8??10-3 mg/kg for Cd2+ ion. The adsorption in a mixture of the metal ions had a balancing effect on the adsorption capacity of the activated carbon. The adsorption capacity of each metal ion was affected by the presence of other metal ions rather than its presence individually. The study showed the presence of other heavy metals attribute to the reduction in the activated carbon capacity, and the adsorption process was found to obey the Freundlich isotherm for both ions.
Kannan et al., (2009) was studied on the removal of lead(II) ions by adsorption ontoindigenously prepared bamboo dust carbon (BDC) and commercial activated carbon (CAC). It has been carried out with an aim to obtain data for treating effluents from metal processing and metal finishing industries. Exactly 50 mL of lead(II) ion solution of known initial concentration was shaken with a required dose of adsorbent (CAC=4-22 g/L and BDC=10-28 g/L) of a fixed particle size (CAC=90 micron and BDC=45-250 micron) in a thermostatic orbit incubator shaker (Neolab, India) at 200 rpm after noting down the initial pH of the solution (pH = 7.2).Effect of various process parameters has been investigated by following the batch adsorption technique at 30+1??C. Percentage removal of lead(II) ions increased with the decrease in initial concentration and increased with increase in contact time and dose of adsorbent. Amount of lead(II) ions adsorbed increases with the decrease in particle size of the adsorbent. As initial pH of the slurry increased, the percentage removal increased, reached a maximum and the final solution pH after adsorption decreases. Adsorption data were modeled with the Freundlich and Langmuir isotherms, the first order kinetic equations proposed by Natarajan ' Khalaf, Lagergren and Bhattacharya and Venkobachar and intra- particle diffusion model and the models were found to be applicable. Kinetics of adsorption is observed to be first order with intra-particle diffusion as one of the rate determining steps. Removal of lead(II) ions by bamboo dust carbon (BDC) is found to be favorable and hence BDC could be employed as an alternative adsorbent to commercial activated carbon (CAC) for effluent treatment, especially for the removal of lead(II) ions.
Activated carbon prepared from Elais Guineensis kernel or known as palm kernel shell could be used as an effective adsorbent material for the treatment of copper aqueous wastewater. This work was done by Najuaet in the year of 2008. The adsorption of copper on activated carbon is found to be pH, initial concentration a nd dose dependent. The optimum conditions of copper uptake obtained from this study are: pH 5.0, initial concentration 50 mg/L and biomass loading of 1.0 g. In addition, the correlation of Temkin adsorption isotherm fits the experimental data most accurately. It was determined that the maximum adsorption capacity is 3.9293 mg/g. The material (Elais Guineensis kernel) is not only economical, but also is an agricultural waste product. Hence activated carbon derived from Elais Guineensis kernel would be useful for the economic treatment of wastewater containing copper metal.
Hefneet al., (2008), worked on the adsorption of Pb(II) from aqueous solution by using natural and treated bentonite. Lead (Pb) is one of the major environmental pollutants. Adsorption appears to be the most widely used for the removal of heavy metals. The aim of this work is to investigate the adsorption potential of commercial natural bentonite (NB) in the removal of Pb (II) ions from aqueous solution. The effects of different variables, such as, concentration of Pb, mass of NB, pH, time, NB washing and heat treatment and temperature was investigated. The bentonite sample under the heat and washed treatment are labeled as CB and WB respectively. The adsorption experiments were carried out using batch process. The equilibrium time for Pb (II) adsorption on NB was 5 min, the processes conforming to second order kinetics. NB had a much higher adsorption capacity for Pb (II) with the Langmuir monolayer capacity (qm) of 107, 110 and 120 mg g-1 at 293, 313 and 333 K respectively compared to others adsorbents. Thermodynamic parameters such as 'H??, 'S?? and 'G?? were calculated. The adsorption process was found to be endothermic and spontaneous. The enthalpy change for Pb(II) by NB adsorption has been estimated as 33 kJ mol-1 indicating that the adsorption of Pb(II) by NB corresponds to a physical reaction. The adsorption capacity of washed bentonite WB was very high compared to NB and CB.
Investigation was done for the adsorption of chromium (VI) ions on wheat bran using batch adsorption techniques by Nameni in the year of 2008. The main objectives of this study are to: 1) investigate the chromium adsorption from aqueous solution by wheat bran, 2) study the influence of contact time, pH, adsorbent dose and initial chromium concentration on adsorption process performance and 3) determine appropriate adsorption isotherm and kinetics parameters of chromium (VI) adsorption on wheat bran. The results of this study showed that adsorption of chromium by wheat bran reached to equilibrium after 60 min and after that a little change of chromium removal efficiency was observed. Higher chromium adsorption was observed at lower pH, and maximum chromium removal (87.8 %) obtained at pH of 2. The adsorption of chromium by wheat bran decreased at the higher initial chromium concentration and lower adsorbent doses. The obtained results showed that the adsorption of chromium (VI) by wheat bran follows Langmuir isotherm equation with a correlation coefficient equal to 0.997. In addition, the kinetics of the adsorption process follows the pseudo second-order kinetics model with a rate constant value of 0.131 g/m.min-1. The results indicate that wheat bran can be employed as a low cost alternative to commercial adsorbents in the removal of chromium (VI) from water and wastewater.
Akporhonor et al., (2007) was investigated that removal of Zn, Ni and Cd ions from aqueous solution by adsorption onto chemically modified maize cobs. Maize cob carbon was prepared by pyrolysis at 300 and 400oC for 35 min. This was followed by steeping in saturated ammonium chloride. The activated carbon which was characterized for bulk density, surface area, surface area charge, abrasion resistance and pH was used in the removal of Cd2+, Ni2+, Cd2+ and Zn2+. The surface areas of the maize cob carbon at 300 and 400oC were 0.010 and 0.021 g sample per mg iodine, respectively. The effectiveness of the modified maize cobs in removing the metal ions from solution was found to be Zn >Ni> Cd. The removal efficiency of the metal ions is depended on the metal ion concentration and temperature of carbonization.
Removal of Pb(II) from wastewater by using green algae cladophorafascicularis biosorption is an effective method to remove heavy metals from wastewater. In this work, Deng was found that the adsorption features of cladophorafasciculariswere investigated as a function of time, initial pH, initial Pb(II) concentrations, temperature and co-existing ions. kinetics and equilibria from batch experiments in the year of 2007. The bio-sorption kinetics followed the pseudo-second order model. Adsorption equilibria were well described by the Langmuir and Freundlich isotherm models. The maximum adsorption capacity was 198.5 mg/g at 298K and pH 5.0. The adsorption processes were endothermic and the bio-sorption heat was 29.6 kJ/mol. Desorption experiments indicated that 0.01 mol/L Na2EDTA was an efficient desorbent for the recovery of Pb(II) from biomass. IR spectrum analysis suggested amido or hydroxy, C=O and C'O could combine intensively with Pb(II).
Ngah et al., (2007), worked on removal ofCd, Cu, Pb, Zn, Ni and Cr(VI) ions from industrial wastewater by chemically modified plant waste as adsorbent. A wide range of low-cost adsorbents obtained from chemically modified plant wastes has been studied and most studies were focused on the removal of heavy metal ions such as Cd, Cu, Pb, Zn, Ni and Cr(VI) ions. The most common chemicals used for treatment of plant wastes are acids and bases. Chemically modified plant wastes vary greatly in their ability to adsorb heavy metal ions from solution. Chemical modification in general improved the adsorption capacity of adsorbents probably due to higher number of active binding sites after modification, better ion-exchange properties and formation of new functional groups that favors metal uptake. Although chemically modified plant wastes can enhance the adsorption of heavy metal ions, the cost of chemicals used and methods of modification also have to be taken into consideration in order to produce 'low-cost' adsorbents. Since modification of adsorbent surface might change the properties of adsorbent, it is recommended that for any work on chemically modified plant wastes, characterization studies involving surface area, pore size, porosity, pHZPC, etc. should be carried out. Spectroscopic analyses involving Fourier transform infrared (FTIR), energy dispersive spectroscopy (EDS), X-ray absorption near edge structure (XANES) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy are also important in order to have a better understanding on the mechanism of metal adsorption on modified plant wastes.
Adesolaet al., (2006) was reported that removal of lead ions from dilute aqueous solution using maize (Zea mays) leaf as the adsorbent. The effects of pH, initial metal ion concentration and contact time were studied at 27??C. The analysis of residual Pb (II) ions was determined using atomic absorption spectrophotometer. Maximum adsorption occurred at pH 3. The adsorption isotherms obtained at 27??C and optimum pH fitted well into both the Freundlich and Langmuir isotherms. The Freundlich and Langmuir equations are log '=0.504 log Ce+0.6939 and 1/'= 0.176/Ce'0.03, respectively. The correlation factors are 0.9959 and 0.9939. The result of the pH experiment shows that the initial pH would play a vital role in the removal of the lead ions from solution. The kinetic studies show that uptake of lead ions increases with time and that maximum adsorption was obtained within the first 30 min of the process. These results indicate that maize leaf has potential for removing lead ions from industrial wastewater.
Adsorption of Cu, Ni and Cr by modified oak sawdust was investigated by Argun in the year of 2006. This paper describes the adsorption of heavy metal ions from aqueous solutions by oak (Quercuscoccifera) sawdust modified by means of HCl treatment. The optimum shaking speed, adsorbent mass, contact time, and pH were determined, and adsorption isotherms were obtained using concentrations of the metal ions ranging from 0.1 to 100 mg L'1. The adsorption process follows pseudo-second-order reaction kinetics, as well as Langmuir and D'R adsorption isotherms. The paper discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. The maximum removal efficiencies were 93% for Cu(II) at pH 4, 82% for Ni(II) atpH 8, and 84% for Cr(VI) at pH 3.
Patil et al., (2006) was reported that the conventional powder activated charcoal (PAC) showed more sorption capacity for the removal of nickel than powder babul bark. PAC and PBB are effective at pH 8.0, hence can be efficiently used at pH 7.0 - 8.0, which is more preferable. With the application of very small dose of PBB, it is possible to reduce Ni(II) ion concentration more than 80%, and gives the nickel concentration in the effluent within limits of effluent standards for safe disposal. Recovery and regeneration of PAC is difficult, however PBB can be disposed of safely. Adsorption with low cost adsorbent is not only cheaper but requires less maintenance and supervision. Regeneration is also not required because it can be used once and burnt after drying. It is suggested that the use of powder babul bark (PBB) for removal of nickel from industrial wastewater is an effective and low cost process.
Carbon aerogel as adsorbent for removal of Cd(II), Pb(II), Hg(II), Cu(II), Ni(II), Mn(II) and Zn(II) from aqueous solution was investigated by Meena in the year of 2005. It has been found to be concentration, pH, contact time, adsorbent dose and temperature dependent. Carbon aerogel showed nearly 100% adsorptive removal of heavy metal ions under optimized conditions of dosage10 g/l for aqueous solutions containing 3 mg/l metal ions in 48 h. The adsorption parameters were determined using both Langmuir and Freundlich isotherm models. Surface complexation and ion exchange are the major removal mechanisms involved. The adsorption isotherm studies clearly indicated that the adsorptive behavior of metal ions on carbon aerogel satisfies not only the Langmuir assumptions but also the Freundlich assumptions, i.e. multilayer formation on the surface of the adsorbent with an exponential distribution of site energy. The applicability of the Lagergren kinetic model has also been investigated. Thermodynamic constant (Kad), standard free energy ('G0), enthalpy ('H0) and entropy ('S0) were calculated for predicting the nature of adsorption. The results indicate the potential application of this method for effluent treatment in industries and also provide strong evidence to support the adsorption mechanism proposed.
Nomanbhay et al., (2005) was focused on understanding biosorption process and developing a cost effective technology fortreatment of heavy metals-contaminated industrial wastewater. A new composite biosorbent has been prepared by coating chitosan onto acid treated oil palm shell charcoal (AOPSC). Chitosan loading on the AOPSC support is about 21% by weight. The shape of the adsorbent is nearly spherical with particle diameter ranging 100~150 ??m. The adsorption capacity of the composite biosorbent was evaluated by measuring the extent of adsorption of chromium metal ions from water under equilibrium conditions at 25??C. Using Langmuir isotherm model, the equilibrium data yielded the following ultimate capacity values for the coated biosorbent on a per gram basis of chitosan: 154 mg Cr/g. Bioconversion of Cr (VI) to Cr (III) by chitosan was also observed and had been shown previously in other studies using plant tissues and mineral surfaces. After the biosorbent was saturated with the metal ions, the adsorbent was regenerated with 0.1 M sodium hydroxide. Maximum desorption of the metal takes place within 5 bed volumes while complete desorption occurs within 10 bed volumes. Details of preparation of the biosorbent, characterization, and adsorption studies are presented. Dominant sorption mechanisms are ionic interactions and complexation.
Removal of Co, Cu,Zn, and Mn ions from metal finishing wastewater by using natural zeolites as adsorbent was reported by Erdem in the year of 2004. Behavior of natural (clinoptilolite) zeolites with respect to Co2+, Cu2+, Zn2+, and Mn2+ has been studied in order to consider its application to purity metal finishing wastewaters. The batch method has been employed, using metal concentrations in solution ranging from 100 to 400 mg/l. The percentage adsorption and distribution coefficients (Kd) were determined for the adsorption system as a function of sorbate concentration. In the ion exchange evaluation part of the study, it is determined that in every concentration range, adsorption ratios of clinoptilolite metal cations match to Langmuir, Freundlich, and Dubinin'Kaganer'Radushkevich (DKR) adsorption isotherm data, adding to that every cation exchange capacity metals has been calculated. It was found that the adsorption phenomena depend on charge density and hydrated ion diameter. According to the equilibrium studies, the selectivity sequence can be given as Co2+>Cu2+>Zn2+>Mn2+. These results show that natural zeolites hold great potential to remove cationic heavy metal species from industrial wastewater.
Hussein et al., (2004), worked on biosorption of for Cr(VI), Cu(II), Cd(II) and Ni(II) from industrial wastewater by using Pseudomonas species. Biosorption experiments for Cr(VI), Cu(II), Cd(II) and Ni(II) were investigated in this study using nonliving biomass of different Pseudomonas species. The applicability of the Langmuir and Freundlich models for the different biosorbent was tested. The coefficient of determination (R2) of both models were mostly greater than 0.9. In case of Ni(II) and Cu(II), their coefficients were found to be close to one. This indicates that both models adequately describe the experimental data of the biosorption of these metals. The maximum adsorption capacity was found to be the highest for Ni followed by Cd(II), Cu(II) and Cr(VI). Whereas the Freundlich constant k in case of Cd(II) was found to be greater than the other metals. Maximum Cr(VI) removal reached around 38% and its removal increased with the increase of Cr(VI) influent. Cu(II) removal was at its maximum value in presence of Cr(VI) as a binary metal, which reached 93% of its influent concentration. Concerning to Cd(II) and Ni(II) similar removal ratios were obtained, since it was ranged between 35 to 88% and their maximum removal were obtained in the case of individual Cd(II) and Ni(II).
Khan et al., (2004) was studied that the adsorption process for the removal of heavy metals from waste streams and activated carbon has been frequently used as an adsorbent. Despite its extensive use in the water and wastewater treatment industries, activated carbon remains an expensive material. In recent years, the need for safe and economical methods for the elimination of heavy metals from contaminated waters has necessitated research interest towards the production of low cost alternatives to commercially available activated carbon. Therefore there is an urgent need that all possible sources of agro-based inexpensive adsorbents should be explored and their feasibility for the removal of heavy metals should be studied in detail. The objective of this study is to contribute in the search for less expensive adsorbents and their utilization possibilities for various agricultural waste by-products such as sugarcane bagasse, rice husk, oil palm shell, coconut shell, coconut husk etc. for the elimination of heavy metals from wastewater.
Removal of cadmium and nickel from sugar industry wastewater by using bagasse fly ash was observed by Gupta in the year of 2003. Batch adsorption experiments were carried out in a series of Erlenmeyer flasks of 100 ml capacity covered with teflon sheets to prevent contamination. The effect of contact time (0'150 min), concentration (2.0' 20.0mg l_1), solution pH (2.0'9.0), adsorbent dose (2.0'20.0 g l-1), particle size (100'150, 200'250 and 300'350 mm), and temperature (30 ??C, 40??C and 50??C). The bagasse fly ash was found to be stable in water, dilute acids and bases. The composition of the adsorbent was SiO2'60.5%; Al2O3'15.4%; CaO'2.90%, Fe2O3'4.90%, MgO'0.81%. The loss on ignition was found to be 16.0% by weight. The density and porosity were found to be 1.01 g cm_3 and 0.36%fraction, respectively were studied. As much as 90% removal of cadmium and nickel is possible in about 60 and 80 min, respectively, under the batch test conditions. Effect of various operating variables, viz., solution pH, adsorbent dose, adsorbate concentration, temperature, particle size, etc., on the removal of cadmium and nickel has been studied. Maximum adsorption of cadmium and nickel occurred at a concentration of 14 and 12mg l_1 and at a pH value of 6.0 and 6.5, respectively. A dose of 10 g l_1 of adsorbent was sufficient for the optimum removal of both the metal ions. The material exhibits good adsorption capacity and the adsorption data follow the Langmuir model better then the Freundlich model. The adsorption of both the metal ions increased with increasing temperature indicating endothermic nature of the adsorption process. Isotherms have been used to determine thermodynamic parameters of the process, viz., free energy change, enthalpy change and entropy change.
Jordao et al., (2002), worked on removal of Cu, Cr, Ni, Zn, and Cd from electroplating wastewater and synthetic solutions by vermicompost of cattle manure. A glass column was loaded with vermicompost, and metal solutions were passed through it. Metal concentrations were then measured in theequate in order to evaluate the amounts retained by the vermicompost. The concentrations of Cd, Cu, Cr, Ni, Zn, Al, Ca, Mg, and Pb were determined in the vermicompost sample before and after elution with the synthetic and effluent solutions. For this purpose, portions of 50mg of the air-dried sample were individually digested at 150??C with 5ml of concentrated HNO3. A second portion of HNO3 (5 ml) was added, and the mixtures were evaporated at 150_C. Concentrated HNO3 (5 ml) and HClO4(5 ml) were then added, with the mixtures being reevaporated to near dryness and finally diluted with deionised water to 25 ml. Measurements of pH, metal concentrations, moistness, organic matter and ash contents, and infrared and XRD spectroscopy were used for vermicompst characterisation. Vermicompost residues obtained from this process were used for plant nutrition in eroded soil collected from a talus near a highway. Metal retention (in g of metal/kg of vermicompost) from effluents ranged from 2 for Cr and Zn to 4 in the case of Ni. In synthetic solutions, the values for metal retention were 4 for Cd and Zn, 6 for Cu and Ni, and 9 for Cr. The results also showed that metal concentrations in the purified effluents were below the maximum values established for waste discharges into rivers by the Brazilian Environmental Standards. The relatively high available Cd concentration of the vermicompost residue resulted in plant damage. This effect was attributed to the presence of Cd in the synthetic solution passed through the vermicompost. The data obtained do not give a complete picture of using vermicompost in cultivated lands, but such values as are determined do show that it can be suitable to remove heavy metals from industrial effluents.

EXPERIMENTAL PROGRAMME
Material and method
Babul (Acacia) wood: -As a natural adsorbent
Babul (Acacia) wood has potential to consider as adsorbent among the available natural resources because of their characteristics and easily availability. Utilization of low cost natural adsorbent for treatment of wastewater containing heavy metals in helpful as simple, effective and economically and babul (Acacia) wood were collected from local market Indore, Madhya Pradesh, India.
Babul (Acacia) wood has considered as an adsorbent for treatment process due to its potential to overcome heavy metals pollutants as well as these materials are too cheaper, renewable and abundantly available than other natural resources.
Babul wood contains arabinose, galactose, rhamnose, glucuronic acid etc.

Fig. 3.1:- Diagram for babul wood pieces
Table 3.1: Characteristics of babul wood is shown in below table:-
Parameters Values
Moisture content 15%
Crude fibre 9.2%
crude protein 13.9%
silica 0.12%
modulus of elasticity 11,060 N/mm2
density 650'830 kg/m3
Ca 2.6%
Mg 0.4%
P 0.1%
Chemicals:
All the chemicals were used of analytical reagent grade, and laboratory grade, ZnCl2, HCl, NaOH chemicals of Merck Ltd, Mumbai (India). And 'Wattman 41 filter paper' was supplied by GE Healthcare Ltd, Buckinghamshire (U.K).
Waste Water Sample:
The rinsing of material after plating operation is required to remove any plating bath solution that may be left on material. Rinsing operation emanates the largest volume of wastewater from metal plating operations. Rinse waters finally become contaminated with varying concentration of heavy metals as per the type of rinsing scheme.
A representative Electroplating waste water sample has been collected from an Electroplating industry located at Pithampur, in Dhar district of Madhya Pradesh.
Sample has been handled in such a way that there was no significant changes in composition occur before the tests are made. Effluent waste water of metal finishing stream has been taken as sample in well clean and adequate plastic container. To minimize the potential for volatilization or biodegradation between sampling and analysis, preservation of waste water sample has been made by keeping samples as cool as possible on ambient condition.
Carbonization and activation
The babul wood was cut into shorter sizes of 1-2 cm long and further reduced to desired sizes. The babul wood material was washed with distilled water for the removal of adherent extraneous matter. The washed material was dried in an oven at 105??C for 17 hours to remove moisture. The material babul wood material to be carbonized is impregnated with a boiling solution of 10 % ZnCl2 for 2 hours and soaked in the same solution for 24 hours. At the end of 24 hours, the excess solution decanted off and air dried. Then the material was carbonized in muffle furnace at 400??C. The carbonized material was cooled at room temperature for 3-5 hours before discharging into a container. It was crushed carefully into powder with the aid of crusher and sieved using sieves to get particles of uniform size and finally activated in a muffle furnace at 800??C for a period of 10 minutes in the absence of air so as to increase the surface area of the sample for adsorption purposes. It was then cooled at room temperature, washed with plenty of water to remove residual acid, dried and powdered [Baseri et al, (2012)]. Activated babul wood carbon was washed then dried for 3 hours in an oven at 150??C. The final product was then kept in an airtight polyethylene bag, ready for use.

Fig. 3.2:- Diagram for activated babul wood carbon after carbonization and activation.
Experimental procedure
To find the optimum dosage, optimum pH and optimum time for the removal of cadmium and copper using babul wood carbon as an adsorbent.
Sorption experiments
Removal of Cd and Cu onto the activated carbon prepared from babul wood was carried out by batch method and the influence of various parameters such as effect of pH; contact time and activated babul wood carbon dosage were studied. The adsorption material was powdered activated babul wood carbon produced for this study. The initial pH and temperature were measured and recorded while the effluents from the bed were collected at different intervals for two hours. For each experimental run, 1 L of metal solution was taken in an agitated vessel, pH was adjusted to the desired value, and a known amount of the activated babul wood carbon was added. This mixture was agitated at room temperature (30 ?? 1oC) and at constant rate of 100 rpm for a prescribed time to attain equilibrium. It was assumed that the applied agitator speed allows all the surface area to come in contact with heavy metals over the course of the experiments. Utilized 'Whatman 41 Filter Paper' for filtration and performed the filtration twice to ensure complete retaining of particulate matter. The concentrations of heavy metal (Cd and Cu) in the samples were measured using an atomic absorption spectrometer (AAS).
removal efficiency were all calculated using equations 1 and 2 respectively recorded metal concentration by the end of each operation was taken as initial one. Effect of pH was studied over the range of 2.5.0-10.5 and pH adjustments were made by the addition of dilute aqueous solution of 0.1M HCl and 0.1M NaOH. Effect of adsorbent dosage was studied in the range of 1.5-9.5 g/l of adsorbent at ambient temperatures and effect of contact time on adsorption was determined at different time intervals over a range of 10-60 hours.
The adsorption capacity and removal efficiency of heavy metal by babul wood activated carbons could be expressed as follows:
"AC = " ((Ci-Cf )??V)/Wg (1)
"RE (%) = " ((Ci-Cf)??100)/Ci (2)
Where
AC is the adsorption capacity of heavy metals, RE (%) is the removal efficiency of heavy metals, Ci (mg/l) and Cf (mg/l) are the concentration of heavy metals before and after adsorption experiments, respectively, V (l) is the solution volume of heavy metal concentration, and wg is the dosage of babul wood activated carbon.
Analytical Procedure for measurement of Cd and Cu by Atomic Absorption Spectroscopy
the volume of a sample (10-50 ??l) is injected into the atomizer
the sample is thermally treated and atomized (duration of measuring cycle is 1-3 min)
absorbance of the element is measured during the atomization step (total absorbance peak and peak of the background signal is recorded)
Steps of the measuring cycle in AAS (According to Richard Kopl??k- Atomic spectrometry)
Injection of the sample (and the modifier) on the wall or on the platform of the tube drying ' evaporation of solvent at a temperature slightly above the boiling point (solutions in diluted HNO3 are dried at 120 ??C); the solution must not boil; duration of drying depends on the sample volume (1-2 s/??l); inert gas flows through the tube.
Pyrolysis ' thermal decomposition at higher temperatures (300-1200??C) decomposition of sample matrix to gaseous products removed by the flow of inert gas e.g decomposition of nitrates: 2M (NO3)2 2MO + 4NO2 + O2 other processes: reaction between the analyzer and the modifier, between matrix components and the modifier duration of pyrolysis: ten seconds.
Atomization ' fast heating to high temperature (1400-2700 ??C) evaporation of the analyte, splitting molecules to atoms: MO M + O total absorbance and background signal are recorded (duration: 3-5 s) just before atomization the flow of inert gas is stopped two possibilities: atomization of the wall, or of the platform
Cleaning ' heating to very high temperature (2400-2700 ??C) for approx. 3 s; inert gas flow removes all evaporated compounds off the atomizer
Cooling of atomizer to laboratory temperature.


Fig. 3.3: Atomic absorption spectrometer block diagram
Reagents and standards
Copper stock solution
Copper, 1000 mg/L dissolve 1.000 g of copper metal in a minimum volume of (1+1) HNO3. Dilute to 1 liter with 1% (v/v) HNO3 (According to Department of energy, Environment and Chemical Engineering, Washington, University in ST. Louis)
Cadmium stock solution
Cadmium, 1000 mg/L. dissolve 1.000 g of cadmium metal in a minimum volume of (1+1) HCl. Dilute to 1 liter with 1% (v/v) HCl.
Standard solution for Cu & Cd
Standard solution for copper
For copper standard solution (1.0 mL = 0.1 mg Cu)- Dilute 100.0 mL of copper stock solution to 1 L with water (According to ASTM D1688 Standard test method for copper in water)
Standard solution for cadmium
For cadmium standard solution, dissolve 0.500 g pure Cd metal in 250 mL of 3% HCl (heat to dissolve). Cool and dilute to 500 mL with 3% HCl. Prepare an intermediate solution (10 mg/mL) by diluting 10 mL of the stock solution to 1 liter with 4% acetic acid. Pipette 3, 5, 10, 15, and 20-mL aliquots into 100-mL volumetric flasks and dilute to volume with 4% acetic acid. These cadmium working standards correspond to 0.3, 0.5, 1, 1.5, and 2 mg/mL Cd.
Procedure
Wastewater samples: Filter the sample passing through 0.45 ??m membrane filter. Instrument operation: Because of differences between makes and models of instruments, it is impossible to formulate detailed operating instructions. Follow manufacturer's recommendation for selecting proper photocell and wavelength, adjusting slit width and sensitivity, appropriate fuel and air or oxygen pressures and the steps for warm-up, correcting for interferences and flame background, rinsing of burner, igniting sample and measuring emission intensity.
Internal-standard measurement: To a carefully measured volume of sample (or diluted portion), each Cd or Cu calibration standard and a blank, add with a volumetric pipette, an appropriate volume of standard lithium solution. Measure the intensity directly.
Bracketing approach: From the calibration curve, select and prepare Cd or Cu standards that immediately bracket the emission intensity of the sample. Determine emission intensities of the bracketing standards (one Cd or Cu standard slightly less and the other slightly greater than the sample) and the sample as nearly simultaneously as possible. Repeat the determination on bracketing standards and sample. Calculate the cadmium or copper concentration by the equation formed by standard calibration curve.

Equipment used for experimental study
Muffle furnace:-
A muffle furnace is usually a front-loading box-type oven for high temperature application such as fusing glasses creating enamel coating, ceramic and soldering and brazing articles. Therefore there is no combustion involved in the temperature control of the system, which allow for much greater control of temperature uniformity and assures isolation of material being heated from the byproducts of fuel combustion.

Fig.:-3.5:- Diagram of Muffle furnace
Specifications
Heavy-duty steel exterior construction.
Interior of ceramic muffle.
Thick ceramic blanket insulation provides excellent protection from heat loss.
Temperature range upto 950oC.
Choice of digital On/Off or PID temperature control.
Electrically operated on 230 Volts AC, Single Phase.
Muffle Size (H x W x D):15 x 15 x 30 cm
Power Rating:3.3 kW
Hot air oven

Fig. 3.6: Diagram of hot air oven
There are electrical device used in experimental activity. Generally, they can be operated from 50 to 150 oC. There are some points which mentioned below:-
Thermostatically Controlled: Temperature is controlled by hydraulic type capillary thermostat to control temperature from 50??C to 250??C+1??C. an L-shaped prismatic thermometer is fitted to the unit for reading the chamber temperature.
Digitally Controlled: Temperature is controlled through a microprocessor based PID digital temperature indicator-cum-controller or through a profile digital microcontroller having 4 programmes each of 16steps (total 64 steps of ramp/soak profile), from ambient to 250??C with an accuracy of ?? 1??C. All digitally controlled ovens are fitted with air circulation fan as standard accessories.
Specications:
These are sturdy double walled units with outer chamber made of M.S. Sheet duly powder coated.
Inner chamber made up of S.S.Sheet (SS-304 grade).
Inner chamber is provided with ribs for adjusting perforated shelves to convenient height.
To work on 220/230 volts A.C.
RESULT AND DISCUSSION
Analysis of electroplating wastewater sample has been made before their treatment in order to evaluate the effluent wastewater characteristics.
Mechanism of adsorption
The mechanism of adsorption is dependent upon the size of the admolecule in comparison with the pore width due to the energetic interactions between the chosen adsorbate and the pores. Admolecules initially adsorb into the pores with the highest energy, ignoring activated diffusion effects, then adsorption proceeds via filling of progressively larger, or decreasing energy, porosity. Some pores are capable of accommodating two or three admolecules and, therefore, may undergo co-operative adsorption effects by reducing the volume element thus increasing the energy and adsorptive potential of the pore.
Adsorption is a mass transfer process which involves the accumulation of substances at the interface of two phases, such as, liquid'liquid, gas'liquid, gas'solid, or liquid' solid interface. The substance being adsorbed is the adsorbate and the adsorbing material is termed the adsorbent. The processes through which some of the fluid phase substances are removed by their transmission to the interface between fluid phase and a solid (separate) phase and accumulation there is called adsorption. Reduction in surface tension between the fluid and the solid phase as a result of the adsorption of fluid phase substances on the solid surface create required driving force for adsorption process.

Fig. 4.1:- Diagram for Adsorption on the surface of activated charcoal
To achieve a very large surface area for adsorption per unit volume, highly porous solid particles with small-diameter interconnected pores are used, with the bulk of the adsorption occurring within the pores.
Thus, during adsorption and ion exchange, the solid separating agent becomes saturated or nearly saturated with the molecules, atoms, or ions transferred from the fluid phase.
The properties of adsorbents are quite specific and depend upon their constituents. The constituents of adsorbents are mainly responsible for the removal of any particular pollutants from wastewater.
Components of fluid phase that adsorb by solid phase is called adsorbed component while the solid porous material is called as adsorbent material.
There are two principal modes of adsorption of molecules on surfaces:
Physical adsorption ( Physisorption).
Chemical adsorption ( Chemisorption).
Physical adsorption (Physisorption)
Physical adsorption occurs when the intermolecular attractive forces between molecules of a solid and the gas are greater than those between molecules of the gas itself. If the interaction between the solid surface and the adsorbed molecules has a physical nature, the process is called physisorption. In this case, the attraction interactions are van der Waals forces and, as they are weak the process results are reversible. Furthermore, it occurs lower or close to the critical temperature of the adsorbed substance.
Chemical Adsorption (Chemisorption)
If the attraction forces between adsorbed molecules and the solid surface are due to chemical bonding, the adsorption process is called chemisorption. Chemisorptions occur only as a monolayer and, furthermore, substances chemisorbed on solid surface are hardly removed because of stronger forces at stake. Under favorable conditions, both processes can occur simultaneously or alternatively. Physical adsorption is accompanied by a decrease in free energy and entropy of the adsorption system and, thereby, this process is exothermic.

Table 4.1:-Difference between physical adsorption and chemical adsorption

The amount of material which is adsorbed on the surface at a particular temperature depends upon the amount of that substance in the gas or liquid phase which is in contact with the surface, and this dependence is called the adsorption isotherm. The isotherm is useful in determining the interactions between the adsorbate and the adsorbent. The extent of adsorption is usually measured by coverage, ?? which is given by
?? = (number of surface sites occupied)/ (total number of surface sites) (4.1)
Langmuir isotherm is concerned with the monolayer coverage of the solid surface by the adsorbate. It assumes that the surface consists of sites onto which the adsorbate can adsorb, and that each site can accommodate one entity at a time. The binding energy at each site is also assumed to be equivalent.
?? = Kp (4.2)
Molecule + Surface site Adsorbed molecule
Where
"K = " "kads" /"kdes" (4.3)
When used in to describe the adsorption of solutes from solution, the Langmuir equation is as follows
"qe = " "qmKLCe" /(1+ "KLCe" ) (4.4)
"qe = " "w" /"m" (4.5)
1/"qe" = 1/"qm" + 1/"qmKL" 1/"Ce" (4.6)
Where Ce is the equilibrium concentration of the adsorbate in the solution, w is the mass of the adsorbate, m is the mass of the adsorbent, qm and kL are Langmuir constants. Hence one should be able to determine qm and kL from a linear plot of 1/qe versus 1/Ce.
When the amount of adsorbent in contact with the solid surface is very low, the linear equation which is used to explain Langmuir isotherm might not be sufficient to explain the adsorption behaviour. For such cases the expression used for Freundlich adsorption isotherm might be more appropriate to use. This modified isotherm is to be expected if the binding energy changes continuously from site to site on solid surfaces.
?? = Kp1/?? (4.7)
When used to describe the adsorption of solutes from solution, this equation would take the form
n = kc1/ ?? (4.8)
To test for agreement one would plot log n against log c and use the slope to evaluate ?? which is an empirical constant which lies between 2 and 10. It has been found that Langmuir and Freundlich isotherms, as well as others, have been very useful in explaining the adsorption behaviour of adsorbate on solid surfaces.

Analysis of electroplating wastewater sample has produced following result.
Table 4.2: Analysis of pretreated electroplating wastewater sample
S. N. Property Report
1 pH 3.0
2 Odor Unpleasant
3 Color Dark black
4 Total solid 23822
5 Dissolved solid 23220
6 Suspended solid 602
7 Conductivity 24170
8 COD 3450
9 Cadmium 1021
10 Copper 896
Note: - All the parameters are expressed in mg/L except pH
Effect of various parameters on heavy metals removal
Effect of pH
pH is one of the most important parameters controlling uptake of heavy metals from wastewater.
It has been reported that the removal efficiency of heavy metals by adsorption is highly dependent on pH values. Hence in order to access the effect of pH on the performance of babul wood, removal efficiency of heavy metals has been examined at different pH range of 2.5-10.5. The COD reduction with pH using constant mass loading of 5.5 g/L of adsorbent material over constant time period of 2 hours is presented in fig. 4.3 and it may be that within pH 2.5 to 10.5, the COD reduction don't change considerably except pH 5.5.
It was also seen that heavy metals removal efficiency of cadmium and copper are maximum at pH 5.5. The analysis data represent the effect of pH on heavy metals removal efficiency of adsorbent.
Table 4.3: Shows the effect of pH on heavy removal by adsorption system.
S. N. pH COD % Cadmium removal % Copper removal
1 2.5 3250 67.11 78.21
2 4.5 2879 74.22 82.11
3 5.5 1511 76.92 89.01
4 8.5 1835 68.53 85.05
5 10.5 2238 63.86 80.23

Fig. 4.2: Effect of pH on percentage heavy removal by adsorption system.

Fig. 4.3: Variation of the value of COD with pH of industrial wastewater sample.


Effect of mass dosages of babul wood carbon on adsorption
The concentration profile of cadmium and copper revealed that the heavy metals removal efficiency has greatly affected by mass dosages of babul wood carbon, but it was also concluded that it is not significant beyond a dosage of 5.5 g/l, beyond this limit of dosing the removal efficiency of heavy metals is not function of mass loading of adsorbent. It is obtained that when using babul wood activated carbon. This alkaline character is believed to be a result of the alkalinity of the carbon, which increases the solution's pH.
Table 4.4: Effect of mass loading of babul wood carbon on adsorption process.
S. N. Mass dosages in g/l pH
1 1.5 3.2
2 3.5 3.5
3 5.5 3.7
4 7.5 4.1
5 9.5 4.2


Fig. 4.4: Effect of mass dosages of babul as potential adsorbent on pH.
The effect of mass dosages of adsorbent on adsorptive treatment of electroplating wastewater had been seen by their heavy metals removal efficiencies. Result shows in below table 4.5:-
Table 4.5: Effect of mass dosages of adsorbent by their heavy metals removal efficiencies.
S. N. Adsorbent dosages in g/l % Cadmium removal % Copper removal
1 1.5 54.22 70.54
2 3.5 64.26 82.39
3 5.5 76.92 89.01
4 7.5 77.95 90.21
5 9.5 81.61 91.61


Fig 4.5: The effect of mass dosages of adsorbent on adsorptive treatment of electroplating wastewater of pH value 5.5on percentage metal removal by adsorption method.
Effect of Contact Time
As contact time increases, concentration of cadmium and copper in the solution decreased rapidly at the beginning and later slows down until it remained constant at about 48 hours, which was then taken as the equilibrium time (Fig.4.6). This indicates that the removal of cadmium and copper ions by activated babul wood carbon was very rapid at the beginning. Most of the maximum percent cadmium and copper removal was attained after about 24 hours. The increasing contact time further do not removed the cadmium and copper and it remains constant after equilibrium reached in 48 hours.
Table 4.6:-Effect of total time of adsorbent by their heavy metals removal efficiencies.
S. N. Contact time (hr) % Cadmium removal % Copper removal
1 12 55.12 67.15
2 24 76.92 89.01
3 36 81.21 90.02
4 48 84.28 93.85
5 60 84.29 93.88


Fig. 4.6: Effect of contact time on the removal of cadmium and copper by activated babul wood carbon.

Develop model equation
Equilibrium Study
Adsorption isotherms are mathematical models that describe the distribution of the adsorbate species among liquid and adsorbent, based on a set of assumptions that are mainly related to the heterogeneity/homogeneity of adsorbents, the type of coverage and possibility of interaction between the adsorbate species. Adsorption data are usually described by adsorption isotherms, such as Langmuir and Freundlich isotherms. These isotherms relate metal uptake per unit mass of adsorbent, qe, to the equilibrium adsorbate concentration in the bulk fluid phase Ce.
Langmuir isotherm
The Langmuir model is based on the assumption that the maximum adsorption occurs when a saturated monolayer of solute molecules is present on the adsorbent surface, the energy of adsorption is constant and there is no migration of adsorbate molecules in the surface plane. The Langmuir isotherm is given by
"qe = " "qmKLCe" /(1+ "KLCe" ) (4.3.1)
"1/qe = " "m" /w (4.3.2) 1/"qe" = 1/"qmKL" 1/"Ce" +1/"qm" (4.3.3)
Where w and m are mass of solute adsorbed and mass of adsorbent, qmandKLare the Langmuir constants, representing the maximum adsorption capacity for the solid phase loading and the energy constant related to the heat of adsorption respectively. qm is calculated by data of slope of eq. 4.3.3
For equilibrium study mass of adsorbent was kept constant and adsorbate concentration was carried. After 24 hrs the Cu concentration and Cd concentration in adsorbent and liquid was determined. It is already shown that 48 hrs is the time to reach the equilibrium (Plot between 1/Ce and 1/qe is shown in Fig. 4.7. From the slop and intercept data the value of qm evaluated.
Table 4.7: Data for Langmuir isotherm from babul wood carbon (a) Cu, (b) Cd.
(a)
m (g) w (g) 1/Ce 1/qe
1.5 0.6320384 2.39443313 2.373273523
3.5 0.7382144 4.678591709 4.741170045
5.5 0.7975296 8.099181074 6.896295761
7.5 0.8082816 9.214504597 9.278944368
9.5 0.8208256 10.91895113 11.5737131

(b)
m (g) w (g) 1/Ce 1/qe
1.5 0.55359 1.184359983 2.709605117
3.5 0.65609 1.79798545 5.334596566
5.5 0.78535 3.332755633 7.003218425
7.5 0.79587 3.535147392 9.423655511
9.5 0.833238 4.437737901 11.40130294

"1/Ce = " "w" /"Co - w" (4.3.4)
Co is initial Cu concentration. 0.896 g/l
Co is initial Cd concentration. 1.021 g/l
(a)

(b)

Figure 4.7: Langmuir plot for adsorption of Cu on (a) Cu, (b) Cd
Co is initial Cu concentration. 0.896 g/l
Cois initial Cd concentration. 1.021 g/l
It can be seen from figure above that the isotherm data fits the Langmuir equation well (R2=0.965 and 0.996). The values of qm found from slope was 2.341 mg/g for Cu and 1.366 mg/g for Cd. It implies monolayer adsorption capacity is (2.341 mg Cu and 1.366 mg Cd) /g of babul wood carbon.
Freundlich Isotherm
The Freundlich isotherm model is an empirical relationship describing the adsorption of solutes from a liquid to a solid surface and assumes that different sites with several adsorption energies are involved. Freundlich adsorption isotherm is the relationship between the amounts of Cu and Cd adsorbed per unit mass of adsorbent w/m and the concentration of the Cu and Cd at equilibrium Ce
qe = Kf.(Ce)1/n (4.3.2)
The logarithmic form of the equation becomes
lnqe = lnKf + (1/n) lnCe (4.3.3)
Where w and m are mass of solute adsorbed and mass of adsorbent, Kf and n are the Freundlich constants, the characteristics of the system. Kf and n are the indicators of the adsorption capacity and adsorption intensity respectively. The ability of Freundlich model to fit the experimental data was examined. For this case, the plot of lnCe vs. ln1/qe was employed to generate the intercept value of Kf and the slope n. The magnitudes of Kf and n shows easy separation of Cu and Cdfrom the aqueous solution and indicatefavourable adsorption.The intercept Kfvalue is an indication of the adsorptioncapacity of the adsorbent; the slope 1/nindicates the effect of concentration on theadsorption capacity and represents adsorption intensity.The Freundlich isotherm is morewidely used but provides no information on the monolayer adsorption capacity incontrast to the Langmuir model. Data of lnqe and lnCe is plotted in Fig. The value of Kf and n was evaluated.
Table 4.8: Data for Freundlich isotherm (a) Cu, (b) Cd.
(a)
m (g) w (g) Ce lnCe lnqe
1.5 0.63204 0.417635384 -0.8731 -0.86427
3.5 0.73821 0.213739531 -1.543 -1.55628
5.5 0.79753 0.123469273 -2.0918 -1.93098
7.5 0.80828 0.108524554 -2.2208 -2.22775
9.5 0.820826 0.091583888 -2.3905 -2.44874

(b)
m (g) w (g) Ce lnCe lnqe
1.5 0.55359 0.84434 -0.1692 -0.9968
3.5 0.65609 0.55618 -0.5867 -1.67421
5.5 0.78535 0.30005 -1.2038 -1.94637
7.5 0.79587 0.28287 -1.2628 -2.24322
9.5 0.833238 0.22534 -1.4901 -2.43373

(a)

(b)

Figure 4.8: Freundlich plot for adsorption of Cu on (a) Cu, (b) Cd
It can be seen from figures above that the isotherm data fits the Freundlich equation well (R2=0.982 and 0.942).

Study of adsorption kinetics
In order to investigate the controlling mechanism of adsorption processes such as mass transfer and chemical reaction, the pseudo-first-order and pseudo-second order equations can be applied to model the kinetics of Cu and Cd adsorption onto activated babul wood powdered with Zncl2.
The pseudo first order rate equation is given as
ln Ct = ln Co - kadt (4.4.1)
Cw = Co - Ct (4.4.2) Where Co and Ct are the initial concentration and concentration of solution (mg/l) at timet, Cw is mass of Cu and Cd (mg) adsorbed, at equilibrium respectively and kadis the rate constant of the pseudo-first-order adsorption process (min-1).Straight line plots of lnCt againstt were used to determine the rate constantkad , and the correlation coefficientsR2.
Since R2 has low value of 0.9325 (for babul wood carbon), it has found from Fig. that adsorption of Cu and Cd on babul wood carbondid not follow pseudo first-order kinetics. It needs to check pseudo second-order kinetics.
Table 4.9 Data for pseudo first order kinetics.

Babul wood carbon
t (hrs) Ct (mg/l) ln Ct
12 1.5 0.405465108
24 3.5 1.252762968
36 5.5 1.704748092
48 7.5 2.014903021
60 9.5 2.251291799

Figure 4.9Pseudo first order kinetics for Cu and Cd adsorption.
Now pseudo-second-order rate equation is given as
t/Cw = 1/h+1/Co (4.4.3)
Where h=kadCo2can be regarded as the initial adsorption rate as t'0 and kadis the rate constant of pseudo second order adsorption (mg/l.min). The plot t/Cwversus t should give a straight line if pseudo-second-order kinetics is applicableand Co, kadand h can be determined from the slope andintercept of the plot, respectively.
The plot of t/Cwversus t for pseudo second order model yields very good straight lines as compared to the plot ofpseudo-first order with correlation coefficient (R2=0.997). This suggests that the adsorption of Cu and Cdbybabul wood carbonfollows the pseudo-second-order kinetic model.
Table 4.10 Data for pseudo second order kinetics.
Cu Cd
t (hrs) Cw (mg/l) t/Cw Cw (mg/l) t/Cw
12 0.601664 19.94468674 0.56278 21.3229
24 0.7975296 30.09292696 0.78535 30.5595
36 0.7975296 45.13939044 0.82915 43.4177
48 0.840896 57.08196971 0.8605 55.7816
60 0.8411648 71.32966097 0.8606 69.7187

Figure 4.10Pseudo second order kinetics for Cu and Cd adsorption.
The value of h and Co evaluated are presented in Table 4.11 below
Adsorbent kad(mg/l.min) Co (mg/L) R2 h
Babul wood carbon (Cu) 0.00000115 896 0.997 0.9248
Babul wood carbon (Cd) 0.000000943 1021 0.9956 0.9834

Comparison of various adsorbents
According to various authors, they have investigated different different types of natural adsorbents for removal of heavy metals like Cu, Cd, Cr etc. and comparison of maximum percentage adsorption capacities of heavy metals are shown below tables with respect the value of pH.:-
Table 4.11 Comparison of various adsorbents
Name of adsorbent pH Percentage Adsorption capacity (Cu) Percentage Adsorption capacity (Cd) Reference
microwave assisted activated carbon 6 99.9 Dutta et al., (2014)
cassava waste 2 99 Phaisanthia,,2013
bagasse fly ash 6 90 Gupta, 2013
Ulgae-seaweed 10 53.13 Muhammad et al., (2012)
Local waste bamboo 8 100 Awoyale, 2012
flamboyant flower 5 Jimoh., 2012
Palms fruits fiber 3 82 Ideriah., (2011)
palm shell activated carbon 5 97 Onundi., 2011
tea waste biomass 5.5 95 Kamsonlian., 2011
cow bone charcoal 5.1 Moreno et al., (2010)
modified oak sawdust 4 93 Argun., 2006
Babul wood carbon 5.5 89.01 76.92 Present study

Hence activated carbon derived from babul wood would be useful for the economic treatment of wastewater containing copper and cadmium metal.

Adsorption column design for adsorption
Batch type sorption is usually limited to the treatment of small volumes of effluent, whereas adsorption column systems have an advantage over this limitation. In adsorption column the adsorbate is continuously in contact with a given quantity of fresh adsorbent thus providing the required concentration gradient between adsorbent and adsorbate for adsorption.
For the adsorption columns design calculations to be carried out, certain assumptions were made. The assumptions made were that:
The process is isothermal
There are no chemical reactions in the column
The bed is homogenous
The concentration gradient in the radial direction of the bed is negligible
The flow rate is constant and does not change with column position.
For powdered babul wood application, isotherm adsorption data can be used in conjunction with a material mass balance analysis to obtain an approximate estimated amount of babul wood carbon that must be added. Because of many unknown factors involved, column and bench scale tests are recommended to develop the necessary data.
If mass balance is written around contactor after equilibrium has been reached.
Amount adsorbed = initial amount of adsorbate present ' final amount of adsorbate present
(4.6.1) "qem = VCo??VCe" (4.6.2)
Where
qe= adsorbent phase concentration after equilibrium, mg adsorbate/g adsorbent
m= mass of adsorbent, g
V= volume, m3
Co= initial concentration of adsorbate, mg/l
Ce= final equilibrium concentration of adsorbate after adsorption has occurred, mg/l
It should be noted that qe is in equilibrium with C if eqn (4.6.2) is solved for qe
"qe = " "V(Co-Ce)" /"m" (4.6.3)
From eqn (4.6.3) is written as follows
"V" /"m" " = " "qe" /"Co-Ce" (4.6.4)
"V" /"m" is the specific volume.
Adsorber column. The volume of the adsorber column can be estimated through the following expression:
V = A*H (4.6.5)
Where
V is the volume of column in m3
A area of adsorber m2
H is Height of column in meter

Contact Time.
"EBCT = " V/Q"e" "= " (LA )/Q"e" (15)
Where
V = bulk volume of babul wood carbon in contactor, m3
A = cross-sectional bed area, m2
L = bed depth, m (ft)
Q = volumetric flow rate, m3/hr
As calculated Contact time is 24 hrs
Column internal diameter is 1.9 meter
Flowrate, Q = 1.09 m3/hr
Area = A=??/(4 )Di2 (4.6.6)
Area, A = 2.54 m2
EBCT (Empty bet contact time) = 24 hrs
Bed height, L = 9 m
Flow rate = velocity*Area
= v*A (4.6.7)
Velocity, v = 0.37 m/hr

The height of the adsorber column, H, should be higher than 1.35 m in order to accommodate a packed bed long (According tothe Royal Society of Chemistry 2004).

Height of column, H = 1.35*9
H = 12.5 m
Volume, V=A*H
= 2.54*12.5
= 36 m2
Column Height, H = 12.5m
Column Diameter, Di = 1.9 m
Bed Height, L = 9 m
Flow rate, Q = 1.09 m3/hr
Contact time = 24 hrs
Area of Column, A= 36 m2
Wastewater flow rate of 1.09 m3/hr is to be treated with activated babul wood carbon to remove heavy metals (copper and cadmium) by using adsorption column and diameter of column 1.9 m.

Optimization of data
1 L of metals solution is taken for batch experiment at ambient temperature and at constant 100 rpm. In this experiment optimum value of various parameter such as pH, contact time and adsorbent dosage was obtained 5.5, 24 hr and 5.5 g/l respectively, which are mentioned below table 4.13:-
Name of parameters Optimum value
pH 5.5
Adsorbent dosage 5.5
Contact time 24 (hrs)

Also verified experimental optimized data in C++ software which are mentioned below:-
#include<iostream.h>
#include<conio.h>
#include<iomanip.h>
#include<math.h>
void main ()
{
clrscr ();
float pH,CT,AD;
//optimization of pH;
cout<<" enter the value of pH="<<endl;
cin>> pH;
if (pH>5.5 && pH<5.5)
cout<<"condition is not not optimized"<<endl;
else
cout<<"condition is optimized"<<endl;
//optimization of CT
cout<<"enter the value of CT="<<endl;
cin>>CT;
if(CT>24 && CT<24)
cout<<"condition is not optimized"<<endl;
else
cout<<"condition is optimized"<<endl;
//optimization of AD
cout<<"enter the value of AD="<<endl;
cin>>AD;
if (AD>5.5 && AD<5.5)
cout<<"condition is not optimized"<<endl;
else
cout<<"conditionis optimized"<<endl;
cout<<"condition is finely optimized";
getch();
}

run
enter the value of pH=
5.5
condition is optimized
enter the value of CT=
24
condition is optimized
enter tHe value of AD=
5.5
condition is optimized
condition is finely optimized

5. CONCLUSION
Following conclusions have been made from the experiment results:-
Treatment of electroplating wastewater by adsorption process using babul wood carbon as an adsorbent has been found effective.
The results show that the removal efficiency of each adsorbent is highly dependent on pH, adsorbent dosage and contact time.
It has obtained that the maximum COD reduction at mass dosage of 5.5 g/l with pH 5.5.
Adsorption of cadmium and copper increased with increase in pH reached maximum at 5.5 pH.
Adsorptive capacity and metal removal efficiency of adsorbent babul wood increased with contact time and reached maximum near at 24 hours.
Adsorption of cadmium and copper on babul wood (treated) were obtained maximum capacity of 1.366 mg/g and 2.341 mg/g respectively at pH 5.5.

Further research needs are identified in the following areas
The effect of pH of low cost adsorbent on the adsorption of heavy metals can be studies.
The effects of carbon content of low cost adsorbent on the adsorption of heavy metals can be studies.

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