Nitrous oxide production in high-loading biological nitrogen removal process under low COD/N ratio condition.
Effects of influent COD/N ratio on N2O 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 N2O production in the bioreactor supplied with low COD/N ratio wastewater was studied using 15N 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 N2O in the bioreactors with influent COD/N ratio less than 3.5. A 15N tracer study showed that this N2O originated from denitrification in anoxic phase. However, N2O reduction capacity of denitrifiers was always larger than NO3(-)-N or NO2(-)-N reduction capacity. It was suggested that a high N2O emission rate under low COD/N ratio operations was mainly due to endogenous denitrification with NO2(-)-N in the later part of anoxic phase. This NO2(-)-N build-up was attributed to the difference between NO3(-)-N and NO2(-)-N reduction capacities, which was the feature observed only in low COD/N ratio operations.
Department of Urban Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. itokawah@jswa.go.jp
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Itokawa
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Hanaki
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Matsuo
D019149:Bioreactors; D008956:Models, Chemical; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D009609:Nitrous Oxide / Q000378:metabolism*; D018505:Waste Management / Q000379:methods*
D009609:Nitrous Oxide; D009584:Nitrogen