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Seasonal Variations and Operational Influences on Microplastic Removal in a Municipal Sequencing Batch Reactor Wastewater Treatment System
Summary
Researchers found that a common wastewater treatment method actually got worse at filtering out microplastics during summer months, sometimes releasing more plastic particles than went in, likely because the treatment process itself broke larger plastic pieces into smaller ones. This matters because it means the water treatment plants we rely on to clean up pollution aren't consistently protecting our waterways from microplastics, which can end up in drinking water, seafood, and eventually our bodies.
Microplastic (MP) pollution in aquatic ecosystems is a critical global concern, with municipal wastewater treatment plants (WWTPs) serving as a primary discharge pathway. This study evaluates the abundance and removal efficiency of MPs within a municipal sequencing batch reactor (SBR) system in Lamphun, Thailand, across three distinct seasons. MP concentrations ranged from 0.11 ± 0.33 to 3.00 ± 2.60 particles/L, with the highest levels observed during summer (2.74 ± 2.49 particles/L)—representing an 85–93% increase compared to rainy and winter seasons. Seasonal operational dynamics significantly influenced SBR performance, yielding removal efficiencies of 33% in the rainy season, 0% in winter, and a negative efficiency (–29%) in summer. These findings suggest that seasonal wastewater characteristics, coupled with particle resuspension and fragmentation, profoundly impact MP retention. While larger MPs (351–1,000 µm) dominated the influent (62%), mechanical stress during aeration promoted fragmentation, increasing the proportion of smaller MPs (<350 µm; 52%) in the effluent. Fibers and fragments were the primary morphologies, with PET and PE identified as the predominant polymers. This study underscores the substantial influence of seasonal conditions on MP dynamics and highlights the necessity for process optimization in conventional SBR systems to mitigate MP discharge into the environment.