ELECTROLYTIC TREATMENT OF TEXTILE WASTEWATER: EFFLUENT TOXICITY ASSESSMENT AND IMPLICATIONS

Electrochemical treatment of simulated textile wastewater containing the azo dye Acid Alizarin Violet N (AAVN) in saline matrix was studied. In modern textile industries, excess amounts of sodium chloride and other salts are used in the dyeing process to assist the exhaustion of anionic dyes. Two bench-scale reactor configurations, split and undivided, with graphite anodes and stainless steel cathodes were used. Dye effluent decolorization was conducted on comparative electrochemical treatment runs in both types of reactors at two levels of applied current, 72 mA and 144 mA, and at two different surface-to-volume ratios, 0.707 m2/m3 and 1.414 m2/m3, in a factorial design at pH 10. Cell performance in terms of color removal was monitored in situ by re-circulating the reactor fluid through a quartz cell placed in the light path of a UV-Vis diode array detector and measuring absorbance at 3 minute intervals. Toxicity of the treated effluents was measured using a Microtox® dose response assay. The split cell configuration exhibited faster color removal and higher end product toxicity. The undivided cell configuration had lower initial decolorization rate and toxicity below the detection level. Increasing applied current increased the initial rate and toxicity. Based on results obtained, a design strategy that maximizes initial decolorization rate is in direct conflict with the goal of minimizing effluent toxicity. This study demonstrates the importance of considering end product toxicity in addition to more traditional criteria in making suitable design decisions for full-scale electrochemical reactors.