Microplastics in an industrial zone wastewater treatment plant: Characterization, fate, and risk assessment

The majority of research on microplastic (MP) characterization and removal has focused on municipal wastewater treatment plants (WWTPs). Hence, this study was performed at an industrial zone WWTP with sectors of textile, plastic recycling, furniture, etc. Three monthly sampling campaigns were conducted to analyze the MPs (abundance, shape, color, size, polymer type), and to investigate their fate and removal rate in the WWTP. Furthermore, the environmental risk assessment using EPI Suite™ modeling was conducted for common MP polymer types. The results indicated that the highest MP concentration was detected in the sludge sample (3,734 MP/L), while the lowest one was observed in the effluent sample (52 MP/L). While large MPs (5 mm - 425 µm) were removed by primary treatment processes, smaller MPs (250-125 µm) showed a tendency for accumulation in the sludge. The most dominant MP shapes were fiber and fragment in both wastewater and sludge samples, while the most dominant polymer types were polypropylene (38%), polyethylene (24%), and polyethylene terephthalate (11%). The environmental risk assessment reveals that polyvinyl chloride, polyethylene terephthalate, and polystyrene, present in minimal quantities in this study, are more likely to impact the growth of living organisms significantly compared to more common polymer types like polypropylene and polyethylene. Although the overall MP removal efficiency of the industrial zone WWTP was 88%, a significant quantity of MPs (1.5x109 MP/day) was still discharged into the Kızılırmak river that is mostly used for irrigation. Effective control/reduction of MP discharge necessitates the implementation of tertiary treatment processes in industrial zone WWTPs to prevent soil pollution.