Manganese oxide reduction in laboratory microcosms

Manganese biogeochemistry holds special interest for the characterization of passive treatment systems designed to treat acidic mine waters while meeting enforceable effluent discharge limits set for manganese. In the present study, an initial anoxic enrichment culture was developed for use as an inoculum in experimental systems. Standard anoxic microcosms capable of reducing manganese from Mn4+ to Mn2+ were established from the initial enrichment and altered to study the effects of electron acceptor availability and inhibitors on manganese reduction. Manganese reduction was not significantly inhibited in aerobic and nitrate amended microcosms; however, systems amended with metabolic inhibitors (sodium azide or sodium molybdate) exhibited significant inhibition of manganese reduction relative to standard microcosms. The presence of iron was found to influence the partitioning of reduced manganese with adsorption becoming more important with increasing iron to manganese ratios.