Polycyclic aromatic hydrocarbons in the centralized wastewater treatment plant of a chemical industry zone: Removal, mass balance and source analysis

Increased attention has been given to the fate of pollutants such as polycyclic aromatic hydrocarbons (PAHs) introduced to the wastewater treatment plants. Dissolved and adsorbed PAHs were detected in the centralized wastewater treatment plant of a chemical industry zone in Zhejiang Province, China. The most abundant PAHs were the low molecular weight PAHs (e.g., Acy, Ace, Flu and Phe), accounting for more than 80% of the total 16 PAHs in each treatment stage. Phase partitioning suggested that the removal of PAHs in every treatment stage was influenced greater by the sorption of particles or microorganisms. The removal efficiencies of individual PAHs ranged between 4% and 87% in the primary sedimentation stage, between 1% and 42% in anaerobic hydrolysis stage, between <1% and 70% in aerobic bio-process stage, between 1.5% and 80% in high-density clarifier stage, and between 44% and 97% in the whole treatment process. Mass balance calculations in primary stage showed significant losses for low molecular weight PAHs and relatively good agreements for high molecular weight PAHs as well as in anaerobic hydrolysis, high-density clarifier stage and sludge stream for most PAHs. Great gains of 60%-150% were obtained for high molecular weight PAHs in aerobic bio-process stage due to biosorption and bioaccumulation. Our investigations found that PAHs entering the wastewater treatment plant (WWTP) could be derived from the dyeing chemical processes as the byproducts, and the contribution supported by the largest dyeing chemical group was up to 48%.