Nitrous oxide production in high-loading biological nitrogen removal process under low COD/N ratio condition

Effects of influent COD/N ratio on N(2)O emission from a biological nitrogen removal process with intermittent aeration: supplied with high-strength wastewater, were investigated with laboratory-scale bioreactors. Furthermore, the mechanism of N(2)O production in the bioreactor supplied with low COD/N ratio wastewater was studied using (15)N tracer method, measuring of reduction rates in denitrification pathway, and conducting batch experiments under denitrifying condition. In steady-state operation, 20-30% of influent nitrogen was emitted as N(2)O in the bioreactors with influent COD/N ratio less than 3.5. A (15)N tracer study showed that this N(2)O originated from denitrification in anoxic phase. However, N(2)O reduction capacity of denitrifiers was always larger than NO(3)(-)-N or NO(2)(-)-N reduction capacity. II was suggested that a high N(2)O emission rate under low COD/N ratio operations was mainly due to endogenous denitrification with NO(2)(-)-N in the later part of anoxic phase. This NO(2)(-)-N build-up was attributed to the difference between NO(3)(-)-N and NO(2)(-)-N reduction capacities, which was the feature observed only in low COD/N ratio operations. (C) 2001 Elsevier Science Ltd. All rights reserved.