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

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 21,800 MPN/100 mL (median inflow) to 126 MPN/100 mL (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 8 μg/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.