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 M n2+ and NH4+, the first to be removed was NH4+, which was oxidized to NO2-, After both NH4+ and NO2- were completely oxidized to NO3-, the r emoval of Mn2+ commenced. Batch experiments showed that the addition o f 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 Mn2+ and could reduce the removal rate by half. In this respect, NO2--mediated chemical reductio n of manganese oxide was demonstrated at slightly acidic pH values. In pure cultures of Nitrosomonas europaea and Nitrobacter winogradskyi, no Mn2+ oxidation occurred, but reduction of MnO2 to Mn2+ was found wh en NO2- accumulated. These results indicate that the development of NO 2- oxidizers is critical in the removal of Mn2+ in rapid sand filters. By oxidizing NO2-, NO2- oxidizers eliminate the negative effect of NO 2- on the biological oxidation of Mn2+.