Removal of iron and manganese from hydrocarbon-contaminated groundwaters

High iron and manganese concentrations were detected in oil-contaminated gr oundwater pumped from a hydraulic barrier at an abandoned refinery site. Th e biological treatment for hydrocarbon removal occasionally showed high iro n and manganese removal efficiencies, therefore a tighter control was put o n the process in order to favour the precipitation of metals. The full-scal e treatment plant was monitored over a period of more than two years, and d ifferent corrective management strategies were adopted by improving the con ditions for (iron and) manganese oxidation. Manganese oxidation and consequ ent precipitation was found to be strongly dependent on parameters such as redox potential, temperature and sludge age. The process was favoured by bi ological activity (nitrification), and laboratory tests showed that the lat ter may be critical for the start up of manganese oxidation, which then pro ceeds mainly by autocatalytic reaction. (C) 2000 Elsevier Science Ltd. All rights reserved.