The fate and enhanced removal of polycyclic aromatic hydrocarbons in wastewater and sludge treatment system: A review

As wastewater treatment plant (WWTP) is considered as an important discharge source of polycyclic aromatic hydrocarbons (PAHs) into the environment, many investigations have been carried out to study the behaviors of PAHs in WWTPs. This review focuses on the fate and enhanced removal of PAHs in wastewater and sludge treatment and disposal processes. Firstly, it is found that the occurrence of PAHs in wastewater and sludge depends on the local industrialization and standard. Low-molecular-weight (LMW) PAHs are dominant in wastewater while high-molecular-weight (HMW) ones are dominant in sludge. Then, the fate of PAHs in different treatment processes are discussed in detail. LMW PAHs can be biodegraded by microorganisms while HMW ones are transferred from wastewater to sludge by adsorption. Among sludge treatment techniques, only anaerobic digestion can remove part of PAHs. Compost results in PAHs migratation to other systems, and incineration produces PAHs for incomplete combustion. Also, the enhanced removal strategies of PAHs are reviewed. PAHs removal can be enhanced by increasing their solubility and the activity of microbes, and PAHs generation can be reduced by using Ca-based additives and co-fuel. Finally, the key points for future investigation on PAHs fate and removal in wastewater and sludge treatment are proposed.