INFLUENCE OF ENVIRONMENTAL-CONDITIONS ON THE AMOUNT OF N2O RELEASED FROM ACTIVATED-SLUDGE IN A DOMESTIC WASTE-WATER TREATMENT-PLANT

Waste water purification is characterized by intensive mineralization and nitrification processes. Because of the high O-2 demand, temporari ly anaerobic conditions may be produced. and denitrification by nitrif ying organisms as well as hetertropic denitrification may contribute t o N2O release. In situ measurements (1993-1994) suggest that N2O is re leased from activated sludge in a domestic waste water treatment plant at an average rate of 1040 mu g m(-2) h(-1) with a range between zero and 6198 mu g m(-2) h(-1). The production of N2O seems to be related to the concentration of NO2- and NO3- as well as to the pH. In the was te water about 75-200 mu g N2O l(-1) is dissolved. This N2O is release d after discharge into the receiving waters. The N2O is produced essen tially by nitrification rather than by heterotropic denitrification. O n a long-term scale the increasing use of mechanical-biological waste water purification plants world-wide may add increasingly to the anthr opogenic production of N2O, although the present amount of N2O produce d is negligible compared to its global terrestrial production.