Microplastics in wastewater treatment plants: A review of the occurrence, removal, impact on ecosystem, and abatement measures

Microplastics are ubiquitous in the environment which has attracted increasing environmental, health, socio-economic, and regulatory concerns. Exposure to these emerging pollutants has been associated with certain disorders in both animals and humans. Wastewater treatment plants (WWTPs) are a reservoir of microplastics due to the diverse influent sources. They also serve as a point source of microplastics pollution in the environment due to their inability to completely remove these pollutants in the final effluent. The present review discusses the physicochemical properties - shapes, polymer composition, and sizes of microplastics present in WWTPs. The impact of these properties on microplastics removal efficiency in WWTPs and the other factors influencing their occurrence and removal are further elucidated. The impact of effluent microplastics on the environment is also provided. Finally, microplastics abatement measures such as redesigning washing machine filters and the efficacy of policies on regulating plastics pollution are highlighted. Investigations into microplastics mass instead of particle number only, will constitute a future research direction which will increase our understanding of microplastics nexus in wastewater pollution and treatment.