Removal of iron and manganese from hydrocarbon-contaminated groundwaters

High iron and manganese concentrations were detected in oil-contaminated groundwater pumped from a hydraulic barrier at an abandoned refinery site. The biological treatment for hydrocarbon removal occasionally showed high iron and manganese removal efficiencies, therefore a tighter control was put on the process in order to favour the precipitation of metals. The full-scale treatment plant was monitored over a period of more than two years, and different corrective management strategies were adopted by improving the conditions for (iron and) manganese oxidation. Manganese oxidation and consequent precipitation was found to be strongly dependent on parameters such as redox potential, temperature and sludge age. The process was favoured by biological activity (nitrification), and laboratory tests showed that the latter may be critical for the start up of manganese oxidation, which then proceeds mainly by autocatalytic reaction.