Industrial wastewater pretreatment steps as an important barrier for microplastics emissions into the aquatic environment

In the debate on microplastic (MP) pathways into the environment, the plastics industry is often highlighted but rarely examined in detail. This study investigates MP emissions captured during wastewater pretreatment at eleven industrial plants in Germany, focusing on plastic producing and processing facilities that produce MP-sized products (<2000 μm). Raw wastewater and pretreatment effluents were analyzed. The MP removal efficiencies of single mechanical pretreatment systems (sedimentation, flotation, chamber filter press, and sand filtration) were examined. Two analytical methods for determining MP mass and MP numbers (particles (MPP) and fibers (MPF)) were used in parallel and compared. Raw wastewater concentrations varied between 1·10 4 –3·10 9 MPP m −3 and 5–6·10 4 mg MP m −3 . Partial flows of wastewater from granulation and pulverization processes contained 2·10 5 –1·10 7 MPP m −3 and 5·10 2 –2·10 4 mg MP m −3 . Discharged wastewater into the sewage system after pretreatment showed lower concentrations of 2·10 3 –5·10 6 MPP m −3 and 5·10 −2 - 5·10 3 mg MP m −3 . Mechanical pretreatment reduced MP concentrations by one to three log levels. Sand filtration and chamber filter press had the highest mean MP removal efficiencies of 99.5% and 99.9%, respectively. No MPF were found. Only the polymer types used or produced were identified at the investigated sites, predominantly as MPP < 500 μm. The results show that established mechanical treatment technologies for particulate matter are effective for MP removal. Moreover, the analysis indicates that mass analysis may serve as a cost-effective and efficient method for MP self-control in industrial settings. • Wastewaters within the plastic production chain show high MP concentrations. • Wastewater pretreatment is a crucial first barrier to prevent MP from entering the environment. • Existing mechanical treatments remove MP sufficiently up to 99.9%. • High MP loads from shaping processes may justify separate wastewater treatment. • Low-maintenance DSC analysis suffices for effluents from plastic facilities.