NITROUS-OXIDE PRODUCTION UNDER TOXIC CONDITIONS IN A DENITRIFYING ANOXIC FILTER

Production of nitrous oxide in a multifed anoxic filter was found duri ng denitrification of wastewaters containing nitrite and nitrate. In t he same reactor three different actions take place: Denitrification of nitrite and nitrate, degradation of formaldehyde (which is used as ca rbon source for denitrification) and urea hydrolysis. Nitrous oxide wa s detected during overloading periods being its concentration increasi ng in the gas phase when formaldehyde accumulates. 1.0% of nitrous oxi de in the gas phase was measured when formaldehyde concentration was i ncreased up to 1500 mg l(-1) in the feeding and the loading rate from 1.5 to 6 g l(-1) d(-1). Formaldehyde was found to be toxic or inhibito ry for denitrification, also observing a 90% urea hydrolysis inhibitio n at formaldehyde concentration over 300 mg l(-1). The presence of nit rous oxide in the gas phase might be used for detecting overloading or anomalous working of denitrifying reactors. (C) 1998 Elsevier Science Ltd. All rights reserved.