Escherichia coli removal in copper-zeolite-integrated stormwater biofilters: Effect of vegetation, operational time, intermittent drying weather

•The first study investigating new biofilter designs with copper-zeolite.•Consistently higher E. coli removal by new designs during 8 months monitoring.•Improved E. coli removal by new designs after extensive drying weather.•Survival of vegetation in new designs. Existing biofiltration systems have shown variable and often inadequate bacterial removal efficacy. Previous work has shown antimicrobial media copper-zeolite as a promising alternative to reduce the variability and excessive discharge of faecal indicator bacteria such as Escherichia coli. A large-scale biofilter column study was conducted over eight months to investigate the benefits of incorporating copper-zeolite into biofilters on E. coli removal. The incorporation of copper-zeolite into biofilters improved E. coli log removal rate by 53% reducing E. coli concentration from 21,800MPN/100mL (median inflow) to 126MPN/100mL (median outflow) comparable to international primary contact recreational water quality. In addition, the E. coli removal performance of copper-zeolite amended biofilters increased after intermittent dry weather periods; this is notable, especially considering biofilter performance usually decreases after drying. Furthermore, these designs reduced inflow copper concentration by 91% (comparable to the metal removal performance of traditional biofilters) and provided a median effluent copper concentration of 8μg/L. The vegetation in copper-zeolite filters survived. These results validate the use of copper-zeolite as bioretention media, particularly for sites requiring microbial reduction. Future research will include systematic investigation of the processes involved in reduction of bacteria in copper-zeolite filters and optimise filter design to augment the system performance to meet more stringent stormwater reuse requirements.