Occurrence and Removal of Microplastics in Wastewater Treatment Plants

Abstract

Microplastics are emerging pollutants that are ubiquitous in a wide range of environments, yet the accumulation of microplastics in wastewater treatment plants is of particular importance because wastewater treatment plants pour their effluents in ecosystems. Here we review microplastics in wastewater treatment plants with emphasis on the sources of microplastics, analytical methods, and removal methods. Sources of primary microplastic in wastewater are from microbeads in personal care products, plastic pellets, and scrubbers used in industry. Secondary microplastics are derived from laundering, tire and road particles, and leachate from landfills. There are various methods for microplastic sampling and identification, yet these methods are not standardized yet. In a conventional wastewater treatment plant, the highest reduction of microplastics occurs during primary treatment during the skimming and settling stage. Microplastics are further removed during sedimentation in secondary treatment. Wastewater treatment plants equipped with membrane bioreactor systems in a tertiary treatment achieved the highest microplastic removal efficiency up to 99.9%. Despite high removal efficiency and low concentration of microplastic in the effluent, a wastewater treatment plant still releases a considerable number of microplastics daily due to the large volume of treated wastewater.