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

The release of nitrous oxide during denitrification in activated sludg e is influenced by various environmental factors. Experiments with dif ferent electron acceptors showed that under anoxic conditions increasi ng concentrations of nitrate as well as nitrite enhance the production of N2O. The N2O concentration in the gas phase increases for 2 h, the n decreases. Nitrite causes a higher release of N2O than nitrate. Acet ate in high concentration can stimulate N2O-release. Without addition of acetate nitrate and nitrite reduction are delayed, and hence N2O-re lease and consumption are much slower. In activated sludge sulfide can play a role as an inhibitor of the nitrous oxide reductase (like in s oil and pure cultures), but is inactivated very rapidly. Repeated addi tion of sulfide can cause a new release of nitrous oxide. At low pH (l ess 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 conditi ons N2O-release and denitrification starts at 0.5-1.0 mg/L DO, but it is not always accompanied by accumulation of nitrite. Further reductio n of the oxygen concentration reduces N2O-release.