Conversion and removal strategies for microplastics in wastewater treatment plants and landfills

Although wastewater treatment plants (WWTPs) have been identified as important collection points and environmental sources for now omnipresent waste in waterways, the contribution of landfills of microplastics (MPs) to environmental pollution has been overlooked. Due to high complexity and large quantity of contaminants in WWTPs and landfills, MPs discharged from these sites may pose greater risks to human and animal health through adsorbed small molecules or microbial biofilms. This review provides a comprehensive summary of current knowledge about the composition and life cycle of MPs in both WWTPs and landfills. We also discuss technologies that could be implemented in WWTPs or landfill leachate treatment facilities to capture MPs and potentially upcycle the polymers to value-added products. Likewise, we examine the challenges of implementing the different technologies given current practices and infrastructure. Finally, we highlight the areas where additional investigation is needed to devise comprehensive strategies for ameliorating the ubiquitous issue of plastic wastes in waterways: (1) the fragmentation process of plastic debris in landfills and occurrence of MPs in leachate; (2) the relationship among complex chemicals, biofilms and MPs, and their effects on wastewater treatment facilities' performance; (3) the development of hybrid processes that leverage current wastewater treatment infrastructure for effective degrading or upcycling MPs and/or nanoplastics.