Occurrence and removal of polycyclic aromatic hydrocarbons and their derivatives in an ecological wastewater treatment plant in South China and effluent impact to the receiving river

Ecological wastewater treatment plant (EWWTP), a kind of emerging wastewater treatment plant (WWTP) in recent years, combined microbiology with botany which is efficient for the removal of nitrogen and organic matter, as well as deodorization. The occurrence and removal of micro-organic pollutants in EWWTPs were still not well known. Polycyclic aromatic hydrocarbons (PAHs) and their typical derivatives (SPAHs) including the oxygenated PAHs (OPAHs), chlorinated PAHs (ClPAHs), and methyl PAHs (MPAHs) were investigated in an EWWTP in Guangdong Province, China. The concentrations of the sigma 6 OPAHs (114-384ng/L) were higher than the sigma 16 PAHs (92-250ng/L), and much higher than the sigma 4 MPAHs (13-64ng/L) and sigma 9 ClPAHs (2-3ng/L) in the EWWTP and the effluent receiving river. The total removal efficiencies of the PAHs, OPAHs, MPAHs, and ClPAHs in the EWWTP (43 +/- 14%, 41 +/- 7%, 55 +/- 16%, and 18 +/- 4%) were lower than the traditional WWTPs, probably due to the lower concentration of the sludge in the ecological treatment. The advanced treatment process (microfiltration and UV disinfection treatment) contributed much less (0-20%) to the whole removal efficiency than the ecological treatment (80-100%). The effluent from the EWWTP slightly reduced the PAHs and SPAHs concentrations in the receiving river. The high concentrations of the PAHs and SPAHs in the receiving river were similar to the influent of the EWWTP, indicating that some untreated wastewater was directly discharged to the river, especially in the upstream.