RELEASE OF NITROUS-OXIDE (N2O) FROM DENITRIFYING ACTIVATED-SLUDGE - VERIFICATION AND APPLICATION OF A MATHEMATICAL-MODEL

The simple mathematical model described in v. Schulthess et al., 1994 [Wat. Sci. Technol. 30(6), 123-132] could only be used for the identif ication of the most important mechanism leading to nitrous oxide (N2O) accumulation in denitrifying activated sludge systems. In this report the mentioned model is extended with the consumption of organic subst rate and with nitrification to predict the nitrous oxide accumulation in continuously fed full scale waste water treatment plants. In full s cale waste water treatment plants the nitrous oxide emission cannot be measured directly. Therefore, a gas stripper for measuring the dissol ved nitrous oxide in the anoxic and aerobic reactor was built. Four ex periments with different operating conditions were performed to verify the model. In these experiments oxygen concentration as well as the n itrogen and organic substrate load were varied. As it was possible to properly describe the experiments with the extended mathematical model it could be used to calculate the N2O emission of a nitrifying/denitr ifying activated sludge system. Even under undesirable operating condi tions (low oxygen concentration in the first reactor) the nitrous oxid e emission is very low as compared to the total nitrogen in the inlet of the plant (< 0.1%).