Emerging concerns of VOCs and SVOCs in coking wastewater treatment processes: Distribution profile, emission characteristics, and health risk assessment

In this study, the distribution profiles, emission characteristics, and health risks associated with 43 volatile and semi-volatile organic compounds, including 15 phenols, 18 polycyclic aromatic hydrocarbons (PAHs), 6 BTEX, and 4 other compounds, were determined in the wastewater treatment plant (WWTP) of a coking factory (plant C) and the succeeding final WWTP (central WWTP). Total phenols with a concentration of 361,000 mu g L-1 were the predominant compounds in the influent wastewater of plant C, whereas PAHs were the major compounds in the final effluents of both coking WWTPs (84.4 mu g L-1 and 30.7 mu g L-1, respectively). The biological treatment process in plant C removed the majority of volatile organic pollutants (94.1%-99.9%). A mass balance analysis for plant C showed that biodegradation was the main removal pathway for all the target compounds (56.6%-99.9%) except BTEX, chlorinated phenols, and high molecular weight (MW) PAHs. Chlorinated phenols and high MW PAHs were mainly removed via sorption to activated sludge (51.8%-73.2% and 60.2%-75.9%, respectively). Air stripping and volatilization were the dominant mechanisms for removing the BTEX compounds (59.8%-73.8%). The total emission rates of the detected volatile pollutants from plant C and the central WWTP were 1,640 g d(-1) and 784 g d(-1), respectively. Benzene from the equalization basins of plant C and the central WWTP corresponded to the highest inhalation carcinogenic risks (1.4 x 10(-3) and 3.2 x 10(-4), respectively), which exceeded the acceptable level for human health (1 x 10(-6)) recommended by the United States Environmental Protection Agency. The results showed that BaP exhibited the highest inhalation non-cancer risk, with a hazard index ratio of 70 and 30 for plant C and the central WWTP, respectively. Moreover, the excess sludge generated during wastewater treatment should also be carefully handled because it adsorbed abundant PAHs and chlorinated phenols at coking plant C (58,000 mu g L-1 and 3,500 mu g L-1) and the central WWTP (622 mu g L-1 and 54 mu g L-1). (C) 2020 Elsevier Ltd. All rights reserved.