INFLUENCE OF NITRATE ON MANGANESE REMOVING MICROBIAL CONSORTIA FROM SAND FILTERS

In microbial consortia from rapid sand filters, manganese and nitrate transformations appear to be linked. Nitrate appears to have a benefic ial effect on the removal of Mn. In aerated batch cultures derived fro m these consortia, the Mn removal rate was 38% higher in the presence of nitrate and was accompanied by nitrite accumulation. There was no i ncrease in Mn removal when ammonium was added to the medium instead of nitrate. (NO3)-N-15 experiments with batch cultures of Mn removing mi xed bacterial cultures showed denitrification. The nitrate profile ins ide bacterial Aocs was determined by means of microelectrode measureme nts. Nitrate uptake inside Aocs grown in the presence of nitrate occur red under both anoxic and aerated conditions. No or a very slight nitr ate uptake occurred in a floc poisoned with 0.2% HgCl2 and a flee grow n in the absence of nitrate, respectively. In microbial Aocs originati ng from two different field sites incubated under anoxic conditions, t he presence of Mn2+ increased the nitrate-N gradient in the flee by 35 -130%. Nitrate also exerted a stabilizing effect on the removal of Mn: microbial consortia were prevented from reducing MnO2 to Mn2+ by the presence of nitrate