Limiting microplastic pollution from municipal wastewater treatment : A circular economic approach

Abstract: The increasing amount of microplastics found in the environment have underscored the urgency to identify, develop and deploy scenarios in which municipal wastewater treatment plants (MWWTPs) limit the release of urban microplastics into the environment. Simultaneously, the global trend towards a circular economy has defined the conditions for these scenarios in relation to the water-energy- nutrient nexus. This study has created a novel framework between studies into treatment technologies for microplastics removal in wastewater streams and circular economic objectives from policymakers with regard to the water-energy-nutrient nexus. The results of this study build on the existing evidence that MWWTPs release significant amounts of microplastics to both terrestrial and aquatic environments. This study has demonstrated how Multi-criteria Analysis (MCA) can be applied to analyse wastewater treatment scenarios for their ability to limit microplastic pollution from MWWTPs, whilst taking the water-energy- nutrient nexus into account. The MCA has identified MBR inci-eco as the best performing circular economic scenario for limiting microplastic pollution from MWWTPs in to be constructed plants. This scenario includes a Membrane Bioreactor (MBR) with Anaerobic Digestion, energy recovery through incineration and Phosphorus recovery through Ecophos. If already existing MWWTPs aim to upgrade their facility to limit microplastic pollution, CASPACUF with Pyreg as an energy-nutrient recovery is seen as the best performing scenario. The powder activated carbon with ultra filtration (PAC-UF) system would then be installed as an additional polishing step to an existing conventional activated sludge (CAS) system, significantly reducing upfront investment costs. Academia can build upon these results to initiate additional research into novel microplastic filtration specific technologies, business model innovation for wastewater treatment and microplastic pollution prevention at the source and in stormwaters. National and international policymakers should ban the distribution and sale of biosolids for direct land application to limit the pollution of microplastics from bio-solids. Furthermore, efforts should be put in place to limit microplastic pollution at the source by stimulating policies for a ban on the use of microbeads, limit tyre wear and improving design for e.q. washing machines.