Optimization the treatment of different classes of textile dyes by electrochemical methods and investigation of reuse the treated water

Dyes are used in the textile industry for the permanent coloring of fabrics and yarns. Certain amount of the dye (almost %30) applied during the coloring of the fabric may pass into the wastewater without being fixed. This wastewater remarks with its intense color concentration, variable pH values and salt content. The biodegradability of dyestuffs, which cause intense color concentration in dyeing wastewater, is limited due to their complex polymer structure, and innovative treatment methods are needed to remove these compounds at the desired level. In this study, synthetic solutions consisting of dye and electrolyte were prepared in order to examine the reuse of water in the treatment of different classes of textile dyes by electrochemical methods. Acid Black 172 (AB172) and Basic Red 46 (BR46) dyestuffs belonging to acid and basic dyestuff classes were used in the experiments designed for determining the effect of dyestuff on the reuse of water in the textile industry. Electrocoagulation (with Fe and Al electrodes) and electrooxidation (Ti/RuO2-IrO2, Ti/IrO2-Ta2O5 and BDD anodes) processes were optimized and water reuse was investigated. Response Surface Method – Box Behnken Design (BBD) was applied to optimize the parameters affecting dyestuff removal. The Design Expert 11.0.1.0 software program was used to perform the BBD experimental design. Initial pH value, applied current value and reaction time, which are operating parameters of EC and EO processes, were chosen as independent variables, and the removal efficiencies of AB172 and BR46 dyestuffs were chosen as model responses. Analysis of variance (ANOVA) was used for checking model fit and data analysis. As a result, when Ti/RuO2-IrO2 electrode is used in the EO process for BR46 dyestuff, and Al electrode is used in the EC process for AB172 dyestuff, it has been observed that color removal and thus water recovery are higher. In the experiments carried out under optimum conditions, the highest removal efficiencies on the basis of dyestuff were 93.4% with the EC process for AB172 dyestuff; for BR46 dyestuff, it is 94% with EO process. In addition, it has been observed that AB172 dyestuff removal with the EC process has lower energy consumption. Evaluations show that the optimum conditions for obtaining the highest removal efficiencies can be determined by applying the developed models. It has been observed that color was removed almost completely by electrochemical methods depending on the experimental conditions (pH, current, reaction time, electrolyte type and concentration etc.). Electrocoagulation, one of the electrochemical methods, provided dyestuff removal less reaction time than electrooxidation, but the formation of dye flocs which must be disposed in the electrocoagulation process, should not be ignored. As a result, electrochemical methods in dyestuff removal are promising processes for the reuse of treated dyeing wastewater and can provide salt recovery and dyestuff savings as well as water recovery.