Microplastics in industrial wastewater treatment plant: Quantification, identification and ecological risk assessment

Abstract

Wastewater treatment plants (WWTPs) are one of the significant pathways of microplastics (MPs) entering the environment. Thus, information regarding this issue is still requisite in Thailand. In this study, wastewater and sludge samples were collected from various treatment units of industrial WWTP in dry season (February 2020) and wet season (July 2020). The MP particles were identified by size, shape, and polymer types. From the wastewater, MPs were detected in the highest amounts after the aeration unit (134.35 ± 20.79 particles/L) in dry season sample. In addition, sludge contained relatively low MPs. The size fraction in wastewater varied, but in sludge was >300 μm commonly in both seasons sample. Fragments and pellets were identified as the most common shape of wastewater and sludge in both seasons sample. The treatment units and sampling period had a significant effect on MP abundance.The distinction might occurred by temporal variation or system operation during the pandemic. Form FTIR result, plastic polymer mainly identified as polypropylene (PP) and polyethylene (PE). The overall removal efficiency was 93.86%, which still discharge to the ocean 108 particles per day. For risk assessment of the effluent, polymer risk index (H) was 230.38 and 203.49 of dry and wet seasons, verify as high value. Moreover, the potential ecological risk (RI) of effluent considered as extreme danger level due to high toxicity polymer from Polymethacrylate (PMMA). SSD method showed that the MP abundance was exceeded the limit value derived from SSD model (HC5 1.143 particles/L), which is relatively low due to selected data. Therefore, the attention must be on WWTPs in Thailand, as they act as the greatest source of MP contamination in the environment and main cause of risk which can affect the ecosystem.