Characterization and removal of microplastics in Guheshwori wastewater treatment plant in Nepal

Contamination of river water systems by microplastic particles (MPPs) is one of the emerging global environmental concerns with potentially widespread ecological, socioeconomic, and health implications. Wastewater treatment plant (WWTP) processes and treats wastewater to remove pollutants and release safe water into the environment. There has been limited research on the characterization of microplastics and their removal at a WWTP in South Asia. In this work, we report on the characterization of microplastics in wastewater and sludge samples (n=300) from Guheshwori WWTP located on the bank of the Bagmati River in Kathmandu representing inlet, secondary aeration tank (SAT), outlet, and sludge from November 2021 to November 2022. On average, we detected 31.2±17.3 MPPs/L, 11.2±9.4 MPPs/L, 7.0±5.6 MPPs/L, and 6.6±4.8 MPPs/g in the samples collected from inlet, SAT, outlet, and sludge, respectively. Commonly found MPPs were in the form of fiber, fragment, foam, and pellet. Largely, MPPs were red, yellow, white, blue, and black in color. The most dominant size fractions were 500 µm – 150 µm in inlet, SAT, and sludge, and 150 µm – 44 µm in the outlet sampling unit. The Guheshwori WWTP was able to remove 77.5% MPPs on average, that mostly occurred in the inlet. The effluent released into the river and the sludge still contained a significant number of microplastics particles.