Wastewater treatment synthetic dyes

In 1980, approximately 111,000 t of synthetic organic dyestuffs were produced in the United States alone. In addition, another 13,000 t were imported. The largest consumer of these dyes is the textile industry accounting for two-thirds of the market (246). Recent estimates indicate 12% of the synthetic textile dyes used yearly are lost to waste streams during dyestuff manufacturing and textile processing operations. Approximately 20% of these losses enter the environment through effluents from wastewater treatment plants (3). 

Specific effluents have also been subjected to WRF-mediated remediation studies. Decolourization, dechlorination and detoxification of highly toxic bleach plant effluents derived from the pulp and paper industry have been reported [26-28], while degradation and decolourization of synthetic dyes due to the non-specificity of the LMEs have been widely documented [29, 30], Likewise, treatment of the acidic, phenolic-rich olive oil mill wastewater has shown COD reduction, decolourization and dephenolization [31-34],... 

But afterwards it was found that facultative microorganisms behave differently in sequential treatment. Sandhya et al. studied the functions of the microaerophilic-aerobic sequential batch reactor for the treatment of synthetic dye wastewater [46]. 

Recent estimates indicate 29t of the synthetic textile dyes used yearly are lost to waste streams during dyestuff manufacturing and textile processing operations. Approximately 20% of these losses enter the environment through effluents from wastewater treatment plants. 

The conventional dyeing of textiles consumes large quantities of water. While much of this water may be recovered, wastewater treatment imposes significant costs. In addition, the hydrophobicity of many synthetic fabrics necessitates the use of dispersing agents and surfactants in the dyeing liquor (Saus et al., 1993). One possible solution to these problems is the use of sc C02 as the solvent. 

Similar results were also obtained by Socha et al. (2005) for the electrochemical treatment of l-Aminonaphthalene-3,6-disulfonic acid (ANDS), a component of the wastewater produced during the synthesis of many synthetic dyes. An increase in the temperature caused a slight increase in the efficiency of the substrate oxidation (Table 2.3), but even at 80°C the removal of TOC and COD was only 18 and 36%, although the decolorization of the solution, i.e., decrease of absorbance, was achieved. 

Commercial synthetic dyes generally contain more than one color product. As the knowledge of the exact composition of dye mixtures is prerequisite for their successful application in many fields of industry and research, many efforts have been devoted for the development of various chromatographic techniques suitable for their separation and quantitative determination. Moreover, the exact determination of the composition and quantity of synthetic dye is required in the control of industrial processes, in the following of efficacy of wastewater treatment, in environmental protection studies, and in forensic science. 

Synthetic dyes, including azo compounds, are widely used as coloring agents in a variety of products such as textiles, paper, leather, gasoline, and foodstuffs. Synthetic dyes persist even after conventional water treatment procedures due to their hydrophilic character and high solubility (they usually bear carboxylic or sulfonic acid groups in their structure) and, therefore, can be distributed in the environment from urban and industrial wastewater. 

Wastewater Treatment by Electrocoagulation, Table 1 Comparison of different treatment strategies for a synthetic contaminated aqueous solutirai of 1 mM phenol and 0.1 mM direct yellow dye 52... 

Yang Q, Lib C, Li H et al (2009) Degradation of synthetic reactive azo dyes and treatment of textile wastewater by a fungi consortium reactor. Biochem Eng J 43 225-230... 

Textile wastewaters can vary from slightly acid to highly alkaline depending on the individual processes carried out within the plant. They generally are alkaline when caustic scouring or mercerizing is involved. Heavy metals such as copper, chromium and zinc result from the use of certain dye carriers in the dyeing operation of synthetic fabrics and of blended fabrics, e.g., cotton and rayon. The pretreatment unit operations which may be necessary for various types of joint treatment facilities are listed in Table 6. 

PMRs coupling photocatalysis with microfiltration (MF) or ultraflltra-tion (UF) have been applied for the degradation of different pollutants, such as pharmaceuticals, humic and fulvic acids, trichloroethylene, bisphe-nol A, chlorophenol, 4-nitrophenol, dyes, as well as for treatment of real dyeing wastewater, synthetic wastewater, grey water and surface waters. 

Solano AMS, Rocha JHB, Fernandes NS, Da Silva DR, Martinez-Huitie CA (2011) Direct and indirect electrochemical oxidation process for decolourisation treatment of synthetic wastewaters containing dye. Oxid Commun 34(l) 218-229... 

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