Innovative bioretention filters effectively remove microplastics from polluted stormwater

Untreated stormwater is a major source of rubber tyre particles and other microplastics present in urban water courses. The aim of this study was to investigate bioretention filters with different sorption materials to clarify sorption processes and determine the removal efficiency of microplastics from urban stormwater. A pilot rain garden facility with 13 bioretention filters was constructed and stormwater from a highway and adjacent impervious surfaces was used for irrigation, and microplastics in inflow and outflow from the filters were studied over 48 months. A combination of the following plants was selected: Armeria maritima, Hippophae rhamnoides, Juncus effusus, and Festuca rubra and were planted in ten filters. These plants were selected because they can stand in water but also withstand droughts, tolerate increased salinity, and can degrade and/or absorb traffic-related pollutants. The innovation with these filters is that they also contain sorbent materials such as waste-to-energy bottom ash, biochar, or Sphagnum peat, mixed with sandy loam. Influent and effluent samples from the filters were taken to evaluate the removal efficiencies of the microplastic polymers analysed with pyrolysis-GC/MS. In the stormwater used for irrigation, and pumped from a stormwater sedimentation chamber, all 13 polymers analysed were quantified in at least one of the samples (n=23), and the following microplastics were present in the highest concentrations: polyisoprene ¿ styrene-butadiene rubber ¿ polybutadiene = polyethylene ¿ polyvinyl chloride ¿ polypropylene ¿polyamide-6,6. The results clearly show that rubber tyre-related polymers dominate in urban stormwater. The preliminary results also showed that all the filters efficiently removed microplastics ¿10 µm up to about 95 Also see: https://micro2024.sciencesconf.org/559610/document