Characteristics of Nitrous Oxide Production Originated from Aerobic Denitrification of Nitrite by Poly-Phosphate Accumulating Organisms

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Potentials of Nitrous Oxide(N_2O) production by Poly-Phosphate Accumulating Organisms(PAOs) were examined to reduce N_2O emission from wastewater treatment plants. Acetic acid, peptone and their mixture were used as organic substrates to cultivate the sludge enriched with different types of PAOs having different denitrification capability. Several findings were obtained as follows ; 1) Rhodocyclus-related PAO(R-PAO) can denitrify nitrite aerobically and produces N_2O as one of some final products. On the other hands, Actinobacteria-related PAO(A-PAO) does have little aerobic denitrification capability, hence, N_2O production is negligible. 2) Influencing factors on N_2O production by R-PAO are nitrite concentration, partial pressure of oxygen, and denitrification capability of R-PAO. The high nitrite concentration causes the higher aerobic denitrification rate of nitrite and the higher nitrite conversion to N_2O. The higher partial pressure of oxygen results in the higher nitrite conversion to N_2O and the lower aerobic denitrification rate of nitrite. Hence, the N_2O production rate depends on their balance. The higher denitrification capability of R-PAO results in the higher aerobic denitrification rate of nitrite and the lower nitrite conversion to N_2O. Hence, the N_2O production rate also depends on their balance.