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Project Name: Anaerobic Digestion of Reactive Dyebath
Country: None Listed
Description: Effluents from textile dyeing and finishing facilities are typically high in color, chemical oxygen demand, and total dissolve solids. These constituents can cause problems at wastewater treatment plants including high oxygen demand, high color in the discharge and aquatic toxicity. The primary cause for aquatic toxicity has often been shown to be high levels of salts, specifically sodium chloride and sodium sulfate. Since most wastewater plants discharge to fresh water systems, aquatic toxicity tests utilize fresh water organisms. These organisms are not tolerant to effluents containing high salt concentrations and thus textile effluents often exhibit high levels of aquatic toxicity. One approach that was evaluated to reduce the salt levels in textile discharges was the reuse of the salt contained in the permeate from nanofiltration. By reuse of the permeate, the salt consumption in the dyeing process can be reduced by around fifty percent. While this approach results in a total reduction of salt used in the dyeing process, concentrates from the nanofilter must be disposed. This concentrate may represent a volume of between two and five percent of the total dyebath volume and contains virtually all of the reactive dyes and other contaminates in a much more concentrated form. Conventional methods of treating the concentrate for color removal and organic reduction have been largely unsuccessful due to the capital and operating expenses involved. A study was performed that evaluated the use of anaerobic treatment of the dyebath concentrate for both color removal and COD reduction. The technical literature had shown that AZO dyes could be effectively decolorized by the use of anaerobic micro-organisms. In addition, anaerobic treatment had been shown to significantly reduce the organic content of wastewaters thus reducing the chemical oxygen demand. Due to the large volume reduction and the concentration of chemical oxygen demanding substances by nanofiltration, the use of anaerobic treatment was shown to be a cost effective alternative. The study used anaerobic batch reactors to evaluate the kinetics of color and COD reduction. This study served to demonstrate the overall feasibility of anaerobic treatment for dyebath concentrate. Based on the results, additional studies were identified to develop full scale design criteria.
 

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