Removal of E. coli from urban stormwater using antimicrobial-modified filter media

Stormwater filters featuring traditional sand filter media cannot reliably treat indicator bacteria for stormwater harvesting. In this work, copper-modified zeolite and granular activated carbon (GAC) were prepared through Cu(2+) impregnation and in situ Cu(OH)2 precipitation. Their antibacterial properties and stability in natural stormwater were studied in gravity-fed columns for 24 weeks, under typical stormwater operational conditions. 11 types of other filter media, prepared using zinc, iron, titanium and quaternary ammonium salts as antibacterial agents, were tested in parallel by way of comparison. Cu(2+)-immobilised zeolite and Cu(OH)2-coated GAC yielded an estimated 2-log reduction of E. coli within 40 min with the presence of other native microbial communities in natural stormwater. Even at high flow velocity (effective contact time of 4.5 min), both media demonstrated 0.8 log removal. Both media and Cu(2+)-treated GAC showed effective inactivation of the removed E. coli during dry periods. Copper leaching from Cu(OH)2-coated GAC was found to be below the NHMRC specified drinking water standard, while that from Cu(2+)-immobilised zeolite varied with the salinity in stormwater. These findings could provide useful information for further development of passive stormwater harvesting systems.