Microplastic removal from urban stormwater: Current treatments and research gaps

Stormwater is a major contributor to microplastic (MP) pollution in the aquatic environment. Although MPs are associated with many toxicological effects, their levels in stormwater are not regulated. This review compared the effectiveness of different MP removal technologies from stormwater runoff and examined the performance of typical stormwater treatment systems for MP removal to assess possible MP pollution control via stormwater management. Bioretention and filtration systems performed similarly with 84-96% MP removal efficiencies. Despite the limited number of studies that focused on wetlands and retention ponds, preliminary data suggested potential for MP removal with efficiencies of 28-55% and 85-99%, respectively. Despite the higher efficiency of bioretention and filtration systems, their removal efficiency of fibrous MPs was not optimal. Furthermore, wetlands were less effective in removing MPs than retention ponds, although the limited data might lead to an inaccurate representation of typical performances. Therefore, more research is required to arrive at definitive conclusions and to investigate alternative treatment options, such as ballasted sand flocculation, flotation, and biological degradation, and evaluate the effectiveness of bioretention and filtration for MPs <100 μm.