Removal of Microplastics by Different Treatment Processes in Shanghai Large Municipal Wastewater Treatment Plants

Abstract

Wastewater treatment plants are important sources of microplastics (MPs) in aquatic environments. The present study was conducted to investigate the number concentration, removal rate, and fate of MPs in two large municipal treatment plants in Shanghai. The MPs number concentration in the influent water of WWTP1 and WWTP2 were (226.27±83.00) piece·L-1 and (171.89±62.98) piece·L-1, respectively. WWTP1 had a MPs removal efficiency of 63.25%, which is slightly higher than that of WWTP2, at 59.84%. The removal efficiency during the primary treatment process of the two sewage treatment plants on MPs accounted for 70%-80% of the whole treatment process. The primary treatment process and secondary treatment process transferred (48.10%±1.62%) and (12.97%±0.05%) of MPs in the sewage to the sludge, respectively. As a whole, (38.82%±1.55%) of MPs in the sewage treatment plants were finally discharged into natural waters, and the remaining (61.18%±1.55%) entered the sludge. This study shows that the removal rate of MPs in Shanghai's municipal treatment plants is low and that after treatment, large amounts still enter the natural waters with the final effluent, which causes significant ecological risks. This study provides basic data of MPs removal and trends of large urban sewage treatment plants in a plain river network area, which can provide reference for further design of MPs removal processes.