Role of autotrophic nitrifiers in biological manganese removal from groundwater containing manganese and ammonium.

Upon start-up of a rapid sand filter fed with groundwater containing Mn(2+) and NH(4+), the first to be removed was NH(4+), which was oxidized to NO2 (-). After both NH(4+) and NO2 (-). were completely oxidized to NO3 (-), the removal of Mn(2+) commenced. Batch experiments showed that the addition of Nitrosomonas europaea and Nitrobacter winogradskyi stimulated the Mn(2+) removal by sandfilter microbial consortia. NO2 (-). was found to have a marked inhibitory effect on the removal of Mn(2+) and could reduce the removal rate by half. In this respect, NO2 (-)-mediated chemical reduction of manganese oxide was demonstrated at slightly acidic pH values. In pure cultures of Nitrosomonas europaea and Nitrobacter winogradskyi, no Mn(2+) oxidation occurred, but reduction of MnO2 to Mn(2+) was found when NO2 (-). accumulated. These results indicate that the development of NO2/(-). oxidizers is critical in the removal of Mn(2+) in rapid sand filters. By oxidizing NO2 (-). NO2 (-). oxidizers eliminate the negative effect of NO2 (-). on the biological oxidation of Mn(2+).