Effect of temperature on anoxic metabolism of nitrites to nitrous oxide by polyphosphate accumulating organisms

Temperature is an important physical factor, which strongly influences biomass and metabolic activity. In this study, the effects of temperature on the anoxic metabolism of nitrite (NO⁻₂) to nitrous oxide (N₂O) by polyphosphate accumulating organisms, and the process of the accumulation of N₂O (during nitrite reduction), which acts as an electron acceptor, were investigated using 91% ± 4% Candidatus Accumulibacter phosphatis sludge. The results showed that N₂O is accumulated when Accumulibacter first utilize nitrite instead of oxygen as the sole electron acceptor during the denitrifying phosphorus removal process. Properties such as nitrite reduction rate, phosphorus uptake rate, N₂O reduction rate, and polyhydroxyalkanoate degradation rate were all influenced by temperature variation (over the range from 10 to 30°C reaching maximum values at 25°C). The reduction rate of N₂O by N₂O reductase was more sensitive to temperature when N₂O was utilized as the sole electron acceptor instead of NO₂, and the N₂O reduction rates, ranging from 0.48 to 3.53 N₂O-N/(hr·g VSS), increased to 1.45 to 8.60 mg N₂O-N/(hr·g VSS). The kinetics processes for temperature variation of 10 to 30°C were (θ₁ = 1.140–1.216 and θ₂ = 1.139–1.167). In the range of 10°C to 30°C, almost all of the anoxic stoichiometry was sensitive to temperature changes. In addition, a rise in N₂O reduction activity leading to a decrease in N₂O accumulation in long term operations at the optimal temperature (27°C calculated by the Arrhenius model).