Advancing biofilter resilience: Stability of copper-zeolite antimicrobial filter media under realistic stormwater and operational conditions

Biofilters integrated with antimicrobial filter media copper-loaded zeolite (ZCu) have shown promising results in microbial elimination during stormwater treatment. However, their longevity relies on the stability of ZCu in a multifaceted system during stormwater operational conditions which remains unknown. This study examined the effluent copper concentrations (ECC) from biofilters layered with 10 cm depth of ZCu for 68 weeks' synthetic stormwater dosing, marking the first investigation of its kind. The influence of design factors and operational conditions was assessed. Non-vegetated design SCu showed the lowest average ECC (6 μg/L) indicating excellent ZCu stability, whereas vegetated designs showed twice or more ECC. Intermittent extreme rainfall significantly reduced ECC but led to spikes of 120–360% during subsequent regular events particularly in vegetated designs. A 2-week drying during the warm season increased ECC across all designs, with up to 88% rise in vegetated designs. Although natural reduction in infiltration rate (unrestricted outflow) did not impact ECC, restricting outflow prolonging the retention time clearly increased ECC. Overall, the vegetated design with L. continentale (LCCu) especially suited for field-scale implementation due to its superior long-term stability, the reported pollutants treatment performance and aesthetic integration. Copper fate and transport in the biofilters were influenced by complex physical, chemical, and biological processes contributing to variability across designs and conditions. Future research should decouple these processes for further optimisation of biofilter design. • Biofilters with copper-loaded media showed ECC below long-term irrigation standards • Biofilter designs SCu and LCCu showed superior stability through 68 weeks operation • Vegetation and intermittent drying increased ECC significantly • Extreme rain reduced ECC but led to spikes during subsequent regular rain events • ECC was unaffected by media arrangement, influent Cu, infiltration rate (unrestricted)