Microplastics pollution from wastewater treatment plants: A critical review on challenges, detection, sustainable removal techniques and circular economy

The wastewater treatment plants (WWTPs) have long been recognized as a potentially significant source of microplastic (MPs) pollution in aquatic environments. It is challenging to precisely detect and efficiently remove MPs from wastewater due to the lack of standard protocol and removal technologies. Although many advances have been made in the characterization and quantification of MPs in wastewater, the polydisperse and degradation-resistant properties of MPs and WWTPs’ broad nature and lack of specific design allow MPs to pass through treatment processes. This review highlights the current understanding on the occurrence, fate and expulsion of MPs, recent detection status, advanced and sustainable removal technologies for MPs in WWTPs and conversion of MPs into renewable energy sources. Specifically, different techniques to collect MPs from sewage sludge and wastewater, pre-treatment, classification approaches and retention of MPs in wastewater are reviewed and analyzed. Previous MPs studies have undoubtedly improved our understanding, but many unanswered questions need to be answered. The main challenges appear to be the harmonization of detection methods and the removal levels of MPs in wastewater and sewage sludge. To address this challenge, an alternative methodological approach for WWTPs effluent sampling was developed that eliminate sample contamination by synthetic fibre deposition during aquatic sample processing. In parallel, the sustainable methodology was developed for the treatment of sewage sludge samples that effectively separates the MPs from the organic and organometal compositions of the sludge samples, achieving an average extraction efficiency of 81.9%. The studies determined that synthetic fibres were released in greater quantities than MPs over the short period during which the samples were collected. Recommendations for further methodological refinement are formulated and the need for authoritative methodological standardization is recognized.