Wastewater Treatment Plants as a Key Source of Secondary Microplastic in the Urban Environment

Microplastics (MPs) have been enlisted as one of the emerging pollutants in urban environments, especially in developing countries. However, wastewater treatment plants (WWTPs) are considered a major source of secondary MP in such areas. During the treatment process, MP is deposited in sludges, thereby sludge acts as a prime sink of MP in the environment. This study aimed to investigate the occurrence, distribution, and characteristics (shape, size, colour, and polymer type) of MPs in sewage sludge (SS) from two selected WWTPs in Uttarakhand, India, operated with different technologies: sequential batch reactor (SBR) (SS-A) and moving bed biofilm reactor (MBBR) (SS-B) located at Dehradun and Rishikesh city, respectively. The load of MP was found to be highest in SS-A sludge (42.40 × 103 particles/kg) as compared to SS-B sludge (32.60 × 103 particles/kg). The respective content of fibre, fragments, and film dominated in SS-A sludge (32.54%, 51.41%, and 16.05%) as compared to SS-B sludge (39.89%, 43.55%, and 16.56%). Toxic polymers like polystyrene and polycarbonate showed dominance in studied WWTPs. In summary, WWTP sludge contains a high load of secondary MPs, which need close attention during its safe disposal in the environment.