Assessment of Microplastic Contamination in Urban Wastewater Treatment Systems: Sources, Impacts, and Mitigation Strategies

Abstract

Microplastics (MPs), defined as plastic particles less than 5 mm in size, have become a widespread environmental pollutant, especially in urban water systems. Wastewater treatment plants (WWTPs) in cities play a crucial role in both the movement and partial reduction of MPs originating from household, industrial, and stormwater sources before they enter natural water bodies. This detailed study evaluates MP pollution in urban WWTPs by investigating their origins, presence, behavior during treatment processes, effects on the environment and health, and possible strategies for mitigation.

Based on an analysis of international literature and compiled case studies, influent microplastic (MP) concentrations generally vary from 0.28 to more than 18,000 particles per liter, with fibers and fragments—commonly polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyamide (PA)—being the most prevalent. Standard wastewater treatment plants (WWTPs) remove 57–99% of MPs during primary treatment, 78–99% in secondary treatment, and up to 90–99+% in tertiary treatment. However, due to the large volumes of effluent, millions of MPs are still released into the environment daily. A substantial amount of MPs (>90% of those removed) is retained in sludge, which presents potential risks when applied to land.

Effects encompass ecotoxicity affecting aquatic life, the spread of pollutants and pathogens, and possible human exposure through water and food chains. Cutting-edge technologies such as membrane bioreactors (MBRs), coagulation-flocculation, ozonation, and filtration demonstrate potential for almost total elimination. This paper suggests comprehensive mitigation strategies, incorporating source reduction, process enhancement, and sludge management. The results highlight the necessity for standardized monitoring and policy measures to reduce MP pollution.