Occurrence of Microplastics across Seasonal Variations in a Municipal Wastewater Treatment Plant in Thailand

The behavior of microplastics (MPs) in aquatic environments is influenced by a variety of factors; however, the impact of seasonal variations and meteorological conditions on MPs remains insufficiently explored and understood. This research investigates the impact of seasonality on the presence, transfer, and removal efficiency of MPs at a wastewater treatment plant (WWTP) in Lampang, Thailand. The study monitored the fate and transport of MPs across the rainy, winter, and summer seasons of 2023 - 2024. The results indicated that the average MP concentration was highest during the rainy season, at 1.20 ± 1.27 particles/L, compared to 0.27 ± 0.50 particles/L and 0.27 ± 0.54 particles/L during the winter and summer seasons, respectively. Statistical analysis using ANOVA confirmed a statistically significant difference in MP abundance among the 3 seasons (p < 0.05). Across all seasons, most MPs detected in the WWTP processes were characterized by sizes of 151 - 350 µm, gray coloration, and fragment shapes. The chemical composition of MPs primarily included polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE). Despite these findings, seasonal trends in MP abundance within the secondary treatment processes were inconsistent. These inconsistencies underscore the necessity for further investigation into the fate and transport of MPs under varying conditions, including overflow scenarios. Furthermore, the design and implementation of effective wastewater management strategies, specifically tailored to seasonal variations, are crucial for improving MPs removal efficiency and minimizing their discharge into natural bodies of water. HIGHLIGHTS Most common microplastics (MPs) detected in the wastewater treatment plant (WWTP) were polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP). The number of MPs in the WWTP during the rainy season was greater than in the winter and summer seasons. Rainfall affects the mobility and transport of MPs to the WWTP during rainy seasons. GRAPHICAL ABSTRACT