Occurrence, Fate, and Removal of Microplastics in Sewage Treatment Plants (STPs)

Abstract

Microplastics (MPs), usually plastic fragments smaller than 5 mm in size, are ubiquitous in the environment and pose an increasing threat to the entire ecosystem as an emerging micropollutant. MPs not only contribute to the accumulation of the plastics in the environment but also get transported into the food chain due to absorption and ingestion by aquatic species. They originate from either the direct environmental discharge of purposefully manufactured microscopic fragments as primary MPs or the fragmentation of large plastic debris by environmental factors as secondary MPs. It is widely speculated that the sewage treatment plants (STPs) are one of the prime conduits for releasing of MPs into the aquatic environment despite some degree of removal in the plants. Therefore, it is imperative to understand the occurrence and fate of MPs in STPs for their effective control. In this context, the current status of the identification, abundance, and removal of MPs in STPs is comprehensively explored. Various protocols for collection, pre-treatment, determination, and characterization of MPs in sewage are outlined and compared. The occurrence of MPs in the STPs in terms of their materialistic composition, shape and sizes, and concentration is summarized. The fate of MPs in various treatment stages in the STPs including entrainment in sewage sludge is also assessed. Further, future prospects on the development of advanced removal techniques are presented for effective MPs control.KeywordsPlastic pollutionPrimary and secondary microplasticsSewageTreatment stagesRemoval techniques