Biological leaching of trace metals from stormwater sediments: influential variables and continuous reactor operation

Abstract

Research was conducted on a bioremediation process for the treatment of urban stormwater sediments contaminated with trace metals. Referred to as bioleaching, the process relies on specific strains of naturally occurring, acid-producing bacteria to reduce the pH of a sediment slurry, thereby solubilizing adsorbed and particulate metals into the liquid phase, for collection and processing. The research was first conducted at the bench-scale to investigate the process and the influence of the variables substrate loading, solids loading, temperature, starting pH, benefit of inoculation, mixing, aeration and grade of substrate used. Of these, it was found that temperature and substrate availability exerted the greatest influence on the acidification process. This information allowed for the design of pilot-scale 100 L continuous bioreactors for treating stormwater sediments. At retention times as low as 1.3 days, these reactors achieved almost complete solubilization of copper and zinc, while chromium and lead were partially removed. These results indicate that bioleaching is a promising alternative for the remediation of these contaminated sediments.