Impact of upgrading wastewater treatment plant on the removal of typical methyl, oxygenated, chlorinated and parent polycyclic aromatic hydrocarbons

Wastewater treatment plant (WWTP) secondary effluent is a main source for polycyclic aromatic hydrocarbons (PAHs) and their derivatives (SPAHs) to wastewater receiving rivers in Beijing. The treatment technologies are being upgraded in the WWTPs as the tertiary treatment. To assess the improvement of the removal efficiencies of PAHs and Sigma PAHs after the treatment upgrading, we investigated 16 PAHs and 4 types of Sigma PAHs in the secondary and tertiary treatment process in 5 major WWTPs. Most of the parent PAHs, methyl PAHs, oxygenated PAHs and chlorinated PAHs were detected in the influent, secondary and tertiary effluent. The concentrations of Sigma PAHs (61 ng/L-529 ng/L) were similar to Sigma PAHs (89 ng/L-474 ng/L), indicating that SPAHs should not be ignored when studying the PAH contamination. SPAHs and SSPAHs were largely removed by the secondary treatment (45%-82%) and less by the tertiary treatment (0%-24%). The removal efficiencies were lower in the secondary and tertiary treatment in WWTPs than in the lab-scale experiment conducted previously, probably a result of the association of PAHs and Sigma PAHs with dissolved organic matters (DOMs) in wastewater. DOMs might be a limiting factor for the removal of PAHs and SPAHs in WWTPs. The estimated yearly loadings of the total PAHs and SPAHs decreased only 21% in the tertiary effluent compared with the secondary effluent in WWTP1 and 9% in WWTP3. Therefore, the upgrading of WWTPs did not efficiently improve the removal of PAHs and SPAHs. DOMs should be further considered for improving the removal of PAHs, SPAHs and similar contaminants in WWTPs. (C) 2017 Published by Elsevier B.V.