INFLUENCE OF SOME ENVIRONMENTAL-CONDITIONS ON N2O-RELEASE BY ACTIVATED-SLUDGE UNDER ANOXIC CONDITIONS

The release of nitrous oxide during denitrification in activated sludge is influenced by various environmental factors. Experiments with different electron acceptors showed that under anoxic conditions increasing concentrations of nitrate as well as nitrite enhance the production of N2O. The N2O concentration in the gas phase increases for 2 h, then decreases. Nitrite causes a higher release of N2O than nitrate. Acetate in high concentration can stimulate N2O-release. Without addition of acetate nitrate and nitrite reduction are delayed, and hence N2O-release and consumption are much slower. In activated sludge sulfide can play a role as an inhibitor of the nitrous oxide reductase (like in soil and pure cultures), but is inactivated very rapidly. Repeated addition of sulfide can cause a new release of nitrous oxide. At low pH (less than 6.5) denitrification is slightly inhibited and N2O-release is 100 times higher than at pH 7.0 to 8.0. Under oxygen-limiting conditions N2O-release and denitrification starts at 0.5-1.0 mg/L DO, but it is not always accompanied by accumulation of nitrite. Further reduction of the oxygen concentration reduces N2O-release.