Increased toxicity of textile effluents by a chlorination process using sodium hypochlorite

Chlorinated textile effluents were tested for their toxicity using differen t bioassays. These assays were the Microtox(R) assay, daphnia (Daphnia simi lis) 48-hr survival test, medaka embryo f 4-day and juvenile 96-hr survival tests, and tilapia (Oreochromis mossambicus) juvenile 96-hr survival test. By comparing the results of toxicity tests on water samples collected at t he instream prior to the chlorination process and at the outlet of the wast ewater treatment facility, we found that wastewater toxicity was obviously increased by chlorination using NaOCl as the oxidant, as evidenced by the d ifferent bioassays used. Because no significant difference was observed in water chemistry, such as pH, DO, and conductivity, the induced-toxicity may be partially attributable to residue chlorine or other chlorinated compoun ds generated by chlorination. Future studies are warranted to identify the cause of the increase in the textile wastewater toxicity.