Fate and occurrence of microplastics in wastewater treatment plants

Microplastics (MP) are commonly present in our daily life. Reported studies on MP pollution revealed that wastewater treatment plants (WWTPs) serve as pathways for MP to enter terrestrial and aquatic ecosystems, causing adverse effects on the quality of water bodies, aquatic life, and even contamination of soil and groundwater. In WWTPs, variable MP removal efficiencies from liquid streams have been reported. However, many MP particles are still discharged into natural water bodies. Concomitantly, the retention of MP in sewage sludge is reported, and thus, understanding MP fate in WWTPs is of great significance towards MP management. This review discusses the most recent research focused on the abundance and removal of MP in WWTPs, the main methodologies applied to MP sampling, extraction, identification, and quantification in WWTPs, and the current knowledge on MP as transport vectors for other (micro)pollutants. The transfer of MP from wastewater to sludge raises environmental concerns, and efforts to optimize the value of sludge within a circular economy are essential. The potential of bioaugmentation strategies with plastic-degrading microorganisms to enhance MP removal emphasizes the importance of ongoing research, although it is still in its early stages. It is essential to improve and standardize methods for MP sampling, extraction, visual inspection, and chemical quantification in wastewater and sludge samples. The necessity for further investigation into MP interactions with other environmental (micro)pollutants and their potential impact on human health is also highlighted.