Removal of microplastics in wastewater treatment plants: insights from a literature meta-analysis

The rising environmental presence of microplastics (MPs) has generated growing concern, particularly regarding their potential environmental and human health risks. Wastewater treatment plants (WWTPs) are key terrestrial pathways for MPs emission into aquatic ecosystems, despite their high MPs removal efficiency. This study analyzes 147 published papers, covering 509 real WWTPs. Over 200 information fields were stored for each case study, including plant configuration, operating parameters, and MPs characteristics (size, polymer type and shape). The database enables comparative analyses of MPs concentrations and removals throughout the WWTPs, evaluating the influence of factors such as treated wastewater origin, treatment level, plant size and location. The meta-analysis on literature data highlights that influent MPs concentrations vary widely, primarily influenced by wastewater origin and WWTP size. Industrial WWTPs show significantly higher influent concentrations than municipal or mixed wastewater, while small-scale plants report lower median values. MPs removal rates vary by treatment level, achieving medians of 45.9% at primary outlet and 95.0% at tertiary outlet. The study also explores the influence of particle size, polymer type, and shape on MPs removals. Despite high overall efficiencies, significant data gaps persist, particularly regarding operating conditions and the fate of MPs in sludge. This work underscores the urgent need for standardized methodologies in MPs sampling, characterization, and analysis. Establishing guidelines for reporting operating parameters will enable more robust evaluations and comparability of WWTPs performances and MPs behavior. Addressing these gaps, will refine strategies to mitigate MPs pollution and improve WWTP designs for environmental protection.