Occurrence\nand Ecological Risk Assessment of Highly\nToxic Halogenated Byproducts during Chlorination Decolorization of\nTextile Printing and Dyeing Wastewater

Textile printing and dyeing wastewater\nis a substantial source\nof highly toxic halogenated pollutants because of the chlorination\ndecolorization. However, information on the occurrence and fate of\nthe highly toxic halogenated byproducts, which are produced by chlorination\ndecolorization of the textile printing and dyeing wastewater, is very\nlimited. In this study, the occurrence of six categories of halogenated\nbyproducts (haloacetic acids (HAAs), haloacetonitriles (HANs), <i>N</i>-nitrosamines (NAs), trihalomethanes, halogenated ketones,\nand halonitromethanes) was investigated along the full-scale treatment\nprocesses of textile printing and dyeing wastewater treatment plants.\nFurthermore, the ecological risk of the halogenated byproducts was\nevaluated. The results showed that the total concentration of halogenated\nbyproducts increased significantly after chlorination. Large amounts\nof HAAs (average 122.1 μg/L), HANs (average 80.9 μg/L),\nTHMs (average 48.3 μg/L), and NAs (average 2314.3 ng/L) were\nfound in the chlorinated textile wastewater, and the results showed\nthat the generations of HANs and NAs were positively correlated with\nthe BIX and β/α index, indicating that the HANs and NAs\nmight form from the microbial metabolites. In addition, HAAs and HANs\nexhibited high ecological risk quotients (>1), suggesting their\nhigh\npotential ecological risk. The results also demonstrated that most\nhalogenated byproducts could be effectively removed by reverse osmosis\ntreatment processes except NAs, with a lower removal rate of 18%.\nThis study is believed to provide an important theoretical basis for\ncontrolling and reducing the ecological risks of halogenated byproducts\nin textile printing and dyeing wastewater effluents.