Synthetic Dyes


Synthetic dyes are extensively used in the textile, leather, paper, rubber, plastics, cosmetics, pharmaceuticals and food industries. Commercially, there are more than 100,000 dyes and over 7x105 tons of dyestuffs produced yearly. Generally, synthetic dyes have complex aromatic structures that make them stable and difficult to biodegrade (Crini., 2006). The dye industry consumes substantial volumes of water and generates a considerable amount of colored wastewater. It is recognized that water quality is highly influenced by the color (Crini., 2006). The presence of very small amounts of dyes in water (less than 1 ppm for some dyes) is highly visible and undesirable. Owing to their solubility, synthetic dyes are common water pollutants and be found in trace quantities in industrial wastewater (Papinutti et al. 2006). It is estimated that 1-15% of the dye is released after processing into wastewaters. Color interferes with penetration of sunlight into waters, retards photosynthes, inhibits the growth of aquatic biota and interferes with gas solubility in water bodies. Furthermore, dye effluent may contain chemicals, which are toxic, carcinogenic, mutagenic or teratogenic in various microbiologic, fish species (Ngah et.al. 2011).

Synthetic dyes are usually added to foodstuffs and soft drinks not only to improve appearance, color and texture, but also to maintain the natural color during the process or storage. This class of compounds has been added legally into foods since the 1880s to make food more attractive and appetizing for customers (Crini., 2006). In recent years, natural food colors have been increasingly used. However, they are relatively unstable and the costs are higher than synthetic food colors. Therefore, synthetic food colors are still used instead of natural colors in many foods such as drinks, candies, and sweets (Demirbas, A., 2009). Many countries regulate the use of some of azo dyes in foodstuffs because they pose a potential risk to human health and are even carcinogenic (Ngah et.al. 2011). The entrance of dye compounds into the environment is a concern due to coloration of natural waters and also due to their toxicity, mutagenicity, carcinogenicity and their biotransformation products (Crini., 2006, Demirbas, A.,2009). The development of chemical and instrumental methods for the separation, identification and quantitative analysis of synthetic food colors has become extremely important for the food and beverage industry to assess the quality and safety of food products (Crini., 2006). The number of works published during the last years demonstrates the importance of this problem and the need for developing fast, accurate and selective techniques for analysis the of synthetic dyes (Demirbas, A., 2009).

During the past three decades, several wastewater treatment methods have been developed for the removal of dyes from industrial effluents and reviewed (Thai et al 2013, Forgacs et al 2004, Robinson et al 2001, Neelanchery et al 2011). Among different methods, adsorption is one of the processes which have been frequently applied in wastewater treatment and especially for dye removal. Comprehensive studies dealing with the treatment of dyeing effluents using these adsorption techniques have been thoroughly reviewed in the literature (Niyaz et al 2011, Gergo et al 2012, Dias et al 2007, Demirbas et al 2009 'activated carbon; Rouzbeh et al 2013, Rahman et al 2013, Gil et al 2011, Liu et al 2007 ' clay as adsorbent, Gupta and Suhas, 2009, Gupta et al 2013, Nikolina et al 2013, Crini, 2006, Crini, 2008, Ferrero 2007, Pokhrel and Viraraghavan, 2004). The availability of agricultural wastes or byproducts in large quantities with adsorbing ability and at low price led to the study of their applicability in waste water treatment (Amran et al 2011, Somasekhar Reddy et al 2012, Nigam et al, 2000). Numerous studies have been conducted to investigate the efficiencies and mechanism of removal of dyes by various types of other low-cost adsorbents (Ferrero, 2007; Hamdaoui, 2006; Ozacar and Sengil, 2005; Batzias and Sidiras, 2004; Aygun et al., 2003; Bouzaida and Rammah, 2002; Ho and McKay, 1998). Other methods for the removal of dyes reviewed by researchers include: Alper et al 2011, Khandegar et al 2013 (electro coagulation); Varma et al 2012 (coagulation/flocculation); Myrna et al 2012 Banat, I.M et al 1996 (microbial degradation); Saratale et al 2011, Pearce et al 2003 (bacterial degradation); Asha Srinivasan et al 2010 (biosorbents); Alvares et al 2001- ozonation; Gogate et al 2004, Hai et al 2007 (hybrid methods).

Different techniques used for the removal of colored dye from wastewater include the following:

a) Membrane separation processes like Reverse osmosis (RO) ( Treffry-Goatly.K et al 1983), Nanofiltration (NF) (Chakraborty.K, et. al.2003; Yazhen.X, et al 1999; Zahrim, A.Y. et. al. 2011, Uzal, N. et. al. 2010, Grzechulska-Damszel, J et. al. 2009, Banerjee, P. et. al. 2011), Micellar enhanced ultrafiltration (MEUF) (Purkait.M.K, et al 2004;Ouni, H.,Dhahbi, M. 2010; Huang, J.-H.; Zhou, C.-F.et. al. 2010) and Membrane-wet oxidation/Membrane processes (A.D. Dhale, V.V. Mahajani., 2000; Lecheng Lei, Xijun Hu et al 1998; C. Das, M. Rungta et al 2008; Tan, L.; Sudan, R.G. 1992; C. Das, S. De et. al.2007)

b) Adsorption on to Agricultural solid waste (C. Namasivayam, D. Kavitha,2002; Gopalswami, P.M,Sivakumar, N et. al. 2010, Feng, Y. Yang, F et. al. 2011), Different bentonites (I. Arvanitoyannis, I. Eleftheriadis et. al.1989), Various types of activated carbon (N. Kannan, M.M. Sundaram,2001; Walker GM, Hansen L et. al. 2003; Al-Degs, Y., Khraisheh et. al. 2001; K. Vijayaraghavan, SungWookWon et. al. 2009; Davis, L., Randal, C., 1978; Tan, B.T.Teng, T.T.Omar, A.K.2000; Graham, N.J.D.; Brandao, C.C.S et. al. 1992; Al-Degs, Y.Kharaisheh, M.A.M et. al. 2000; Bouberka, Z.; Khenifi. A. et. al. 2009) and Surfactant impregnated montmorillonite (Bae .J.-H., D.-I. Song et. al. 2000) which act as adsorbents.

c) Oxidation processes (Neamtu. M., A. Yediler et al 2004; Bali. U.,2004; Marechal.M.L, Slokar YM et. al.1997, Shu, H.Y., Huang, C.R et. al.1994; Bali U., 2004; Zhu, X.; Ni, J.; Wei, J et. al.2011; Shen, C.; Wen, Y et. al. 2011; Ovejero, G.; Sotelo, J.L et. al. 2011; Nadupalli, S., Koorbanally.N, et. al. 2011; Migliorini, F.L., Braga, N.A. et. al. 2011)
d) Ozonations (F. Zhang, A. Yediler et. a.(2004; Reynolds, G., Graham, N et. al.1989; Sheng H. Lin, Chi M. Lin,1993; Chu, W.; Ma, C. 2000;Lin, S.H.; Lin, C.M.,1993)
e) Biological waste treatment (Seshadri S, Bishop PL et. al.1994;Banat IM, Nigam P et. al.1996; Mondal, P.K.; Ahmad, R et. al. 2010; Azmi, W.,Sani, R.K et. al.1998)

In many of these techniques the degree of adsorption is not very high. In recent times the surfactant mediated techniques, CPE and AMF have been found to be very effective adsorbents for many organic pollutants. Hence the present author explored the efficacy of these techniques in producing high degree of adsorption of dyes. The author has chosen Five dyes with different structural properties i.e Bromothymolblue(BTB), Bromophenolblue(BPB), Methylene blue(MB), Erythrosine(ET) and Brillent blue FCF(BBF). Among these, Methylene Blue is basic and remaining are dyes are acidic in nature. Erythrosine is a Xanthene dye, Methylene Blue is Thaizine dye and BTB, BPB, BBF are triphenyl methane type of dyes. BTB, BPB and MB are textile dyes and BB FCF, Erythrosine are food dyes. The results of these investigations are in now reported.

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