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 beneficial effect on the removal of Mn. In aerated batch cultures derived from these consortia, the Mn removal rate was 38% higher in the presence of nitrate and was accompanied by nitrite accumulation. There was no increase in Mn removal when ammonium was added to the medium instead of nitrate. 15NO3 experiments with batch cultures of Mn removing mixed bacterial cultures showed denitrification. The nitrate profile inside bacterial flocs was determined by means of microelectrode measurements. Nitrate uptake inside flocs grown in the presence of nitrate occurred under both anoxic and aerated conditions. No or a very slight nitrate uptake occurred in a floc poisoned with 0.2% HgCl2 and a floc grown in the absence of nitrate, respectively. In microbial flocs originating from two different field sites incubated under anoxic conditions, the presence of Mn2+ increased the nitrate-N gradient in the floc 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