Microplastics removal through water treatment plants: Its feasibility, efficiency, future prospects and enhancement by proper waste management

Abstract

With water treatment plants providing a viable solution for removal of microplastics from the environment, this review examines the overall and stage-wise efficiency of various water treatment technologies in removing microplastics and the technologies for managing water treatment wastes. More than 80 scholarly papers published in the past 10 years were reviewed. This review showed highly variable efficiency of the water treatment technologies with primary treatment of wastewater treatment plant reported to remove 16.5 to 98.4% microplastics. Secondary treatment of wastewater treatment plant has overall microplastics removal efficiency ranging from 78.1 to 100% and stage-wise efficiency from 7% (activated sludge) to 99.9% (membrane reactor). Tertiary treatment removes an overall 87.3% to above 99.9% microplastics. Initial coagulation and sedimentation of drinking water treatment plant can normally remove 1.8% to 54.5% of microplastics though advanced treatment pushes microplastics removal to overall 88.6%. Use of larger-than-normal dose of flocculent experimentally significantly increases microplastics removal up to 62%. The largest fraction of microplastics removed conventionally is trapped in sludge. This review highlights the feasibility of water treatment for removal of microplastics from water sources but reveals sludge and membranes as significant sources of microplastics from water treatment. It recommends enhancement of water treatment through adjustment of coagulants, potential use of emerging sol-gel technology and incorporation of advanced treatment for more efficient removal of microplastics. It advocates thermal pretreatment of sludge to potentially facilitate microplastics breakdown and recycle of membrane to reduce re-entry of microplastics into the environment.