Occurrence, behavior and removal of typical substituted and parent polycyclic aromatic hydrocarbons in a biological wastewater treatment plant

• Methyl-PAHs, oxy-PAHs and PAHs were detected in WWTP, but no nitro-PAHs.
• Both the total inflows and outflows were lower in summer than winter.
• OPAH probably transformed from PAHs especially in summer.
• LMW compounds removed by biodegradation/transformation, volatilization and adsorption.
• HMW compounds mainly removed by adsorption to the sludge.

Wastewater treatment plant (WWTP) effluent is the major source for substituted polycyclic aromatic hydrocarbons (SPAHs) to the receiving rivers, as well as the parent PAHs. Some of the SPAHs showed higher toxicities and levels than their parent PAHs. The occurrence and behavior of typical SPAHs were investigated in a representative biological WWTP in Beijing, China. Methyl PAHs (MPAHs) (149–221 ng/L in the influent; 29.6–56.3 ng/L in the effluent; 202–375 ng/g in the activated sludge), oxygenated PAHs (OPAHs) (139–155 ng/L; 69.9–109 ng/L; 695–1533 ng/g) and PAHs (372–749 ng/L; 182–241 ng/L; 2402–3321 ng/g) existed, but nitrated PAHs (NPAHs) were not detected. 2-Methylnaphthalene, anthraquinone, 9-fluorenone and 2-methylanthraquinone were the predominant SPAHs. OPAHs were deduced to be formed from PAHs especially during summer, based on the ratios variation and removal efficiencies of the two seasons, and the surplus mass in the outflows. Low molecular weight compounds (2–3 rings) might be mainly removed by mineralization/transformation and adsorption in the anaerobic unit, and by volatilization in the aerobic unit. High molecular weight compounds (4–6 rings) might be mainly removed by adsorption in the anaerobic unit. The total outflows of SPAHs and PAHs were 66 g/d in summer and 148 g/d in winter from the WWTP to the receiving river. The percentage of OPAHs was higher in summer than in winter.

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