Biological treatment of a textile effluent after electrochemical oxidation of reactive dyes

In this work, a synthetic textile effluent containing a reactive dye (C.I. Reactive Orange 4) was treated in an electrochemical cell with titanium covered by platinum oxide (Ti/PtOx) electrodes to remove color. The discolored effluent was mixed with other textile mill process effluents (scouring, bleaching, washing, etc.), according to the rate of each effluent in the mill, and was submitted to biological treatment (activated sludge plant). Two biological plants were run simultaneously to evaluate the influence of oxidant products generated during the electrochemical treatment. The final chemical oxygen demand (COD) removal in both plants was 65 to 72%. The yield of the activated sludge plants was not affected by the addition of 10% of the discolored dyeing effluent (even when oxidants products were not removed), which indicates that the previous electrochemical treatment do not produce inhibition effects on the biological plant. However, in the case of direct addition of the discolored effluent, the biological treatment plant required a longer adaptation period. In addition, the electrolytic respirometry tests showed that all the biodegradable organic matter was removed, which implies that the yield in organic matter removal was the maximum possible for this type of treatment.