Impact of secondary effluent from wastewater treatment plants on urban rivers: Polycyclic aromatic hydrocarbons and derivatives.

The growing population in urban area impacted the water quality of the urban rivers receiving treated municipal wastewater. Polycyclic aromatic hydrocarbons (PAHs) and their derivatives (SPAHs) are corresponding to the population density. In this study, the concentrations of 16 PAHs and 17 SPAHs, including 4 methyl PAHs (MPAHs), 4 oxygenated PAHs and 9 chlorinated PAHs were investigated in the major urban rivers receiving the effluent from 5 major wastewater treatment plants (WWTPs) in the mega city Beijing. The concentrations of ΣSPAHs (307 ± 68 ng/L) were similar to ΣPAHs (321 ± 92 ng/L) in the total phase (aqueous + particulate) suggesting that SPAHs in the urban rivers should be taken into consideration. The lower concentrations of ΣPAHs and ΣMPAHs in this study than the wastewater receiving rivers and WWTPs effluent previously (2010-2013), as well as the lower concentration in the heating seasons than the non-heating season in the investigated year implied the reduction of coal combustion for heating and power generation in recent years. Although WWTPs effluent was theoretically the only source to the urban rivers in the investigated season, April and November, PAHs and SPAHs in most rivers were demonstrated to be originated from other unknown sources besides the WWTPs effluent. The reduction from the original source, coal combustion (33% and 30%), was more efficient than from the wastewater treatment upgrading (15%) for the reduction of PAHs and SPAHs in the urban rivers.