Microplastics abundance and characteristics in sewers and correlated wastewater treatment plants: A population density-based approach to microplastics mapping

Microplastics (MPs) are emerging environmental contaminants primarily attributed to anthropogenic activities, with wastewater treatment plants (WWTP) acting as major sources for MPs released into both effluent and sewage sludge. A clear understanding of how MPs contamination varies with population density and building activities is essential for developing effective mitigation strategies. In this study, MPs in wastewater from various campus sewers and a university WWTP were quantified and characterized, with student population fluctuations used to identify key sources of MPs pollution. MPs were extracted via filtration and oxidative digestion and then characterized by laser direct infrared (LDIR) chemical imaging. Results showed significant quantities of MPs in both sewers and the WWTP, with their abundance positively correlated to the increasing population density. Sewer location had the greatest effect on the types and quantities of MPs, with elevated levels of polyamide and polyesters detected at sewers near dining halls and dormitories. Chlorinated polyethylene was detected at high concentrations in the primary clarifier and removed through sludge, whereas polypropylene dominated in the discharged effluent. The WWTP achieved removal efficiencies of 73 % in summer and 90.2 % in fall; however, 83 % of MPs smaller than 50 μm remained in the effluent. These findings highlight the importance of standardized extraction and analytical methods for MPs and emphasize the critical roles of population-related building activities in influencing both MPs abundance and polymer compositions in wastewater systems.