Fate of microplastics in urban wastewater treatment plants and their contribution to the receiving river via effluent discharge

Effluents from wastewater treatment plants(WWTPs) are recognized as an important source for microplastic(MP) pollution in the receiving waters. The removal efficiency of MPs in WWTPs and the discharge flux remain largely unknown. The present study measured the MP abundances in the influents, effluents, and activated sludge in four domestic and one industrial WWTPs in Guangzhou,China. The MP abundance detected in influent samples were approximately one order of magnitude higher than those found in effluents, resulting in high removal efficiencies of MPs(97.4%–98.7%) in these WWTPs. A significant amount of the removed MPs deposited in the activated sludge, with abundances of MPs ranging from 7 to 888 pieces/g dry weight sludge. Microplastics remaining in effluents were discharged into the receiving river with releasing rates of ranging from(1.1±1.0) ×10～7 to(4.54±3.92)×10～9 pieces per day. Results obtained in the present study suggest that the contribution of MPs from WWTPs to the aquatic environment is non-negligible and the application of sludge in the agricultural environment may bring additional MP pollution to agricultural soils.