Removal characteristic of surfactants in typical industrial and domestic wastewater treatment plants in Northeast China

Surfactants are widely used in household and industrial products for cleaning and/or solubilization in our daily life. Therefore, they are finally discharged into wastewater treatment plants (WWTPs), which may be the major point pollution source for environment if they were not completely removed during wastewater treatment. In this study, two typical industrial and domestic WWTPs with different wastewater treatment technologies were considered for the topic. Totally, two types of surfactants were analyzed in 24 h influent and each processing unit effluent. Four linear alkylbenzene sulfonates (LASs) with the alkyl chain from C10 to C13, and two benzalkonium chlorides (BACs) with the alkyl chain of C12 and C14 were selected as target compounds. The total concentrations of LASs in influent varied from 19.2 to 1889 μg/L and LAS-C11 and LAS-C12 were the predominant compounds with the concentration from 6.01 to 641 μg/L and 8.02-674 μg/L, respectively. The total concentrations of BACs were much lower than those of LASs, with the concentration ranging from 0.00935 to 1.85 μg/L. Significant positive correlations were observed between concentrations of LASs and BACs in influent, indicating their same and/or similar sources. Compared with the concentration of influent, the concentration of effluent was much lower, indicating the high removal efficiency by the two wastewater treatment processes. Biological treatment unit and cyclic activated sludge system were the main treatment units for the removing of surfactants, which suggested that these two types of surfactants can be easily degraded under aerobic condition. Seasonal variation indicated that the removal efficiencies of surfactants in autumn were a little higher than those in winter. The results of this study provided new insights into the environmental fate of surfactants in wastewater treatment system.