Analysis of nitrite oxidation process and nitrification performance by nitrogen and oxygen isotope fractionation
Hong Liu1, Wei Zeng1, Mengjia Zhan1
1National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Department of Environmental Engineering, Beijing University of Technology, Beijing 100124, China.
Abstract:
The N and O isotope fractionation effects in NO2--N oxidation and nitrification performance of an activated sludge system treating municipal wastewater are unknown. The nitrifying sludge was cultured under different temperature (33 ± 1 °C, 25 ± 1 °C,and 18 ± 1 °C) and dissolved oxygen (DO: 0.5-1 mg/L, 3-4 mg/L, and 7-8 mg/L). The inverse kinetic isotope effects of N and O (15εNO2 and 18εNO2) were -0.62‰ to -7.08‰ and -0.87‰ to -1.68‰ in the process of NO2--N oxidation, respectively. 15εNO3 gradually increased with increasing of temperature (15εNO3-33°C (14.49‰) > 15εNO3-25°C (10.43‰) > 15εNO3-18°C (7.3‰)), while the 15εNO3:18εNO3 was maintained at 1.02-5.32. The increase of temperature improved the nitrification activity, which promoted the fractionation effect, but the change of DO did not highlight this difference. The exchange of NO2--N and H2O (XNOB) was 32.5 ± 1.5%, and the kinetic isotope effect of H2O participating in the reaction (18εk, H2O, 2) was 22.57 ± 1.79‰, indicating that H2O was involved in the NO2--N oxidation rather than DO. In summary, the elevated temperature enhanced the fractionation effect of NO2--N oxidation. This study provides a new perspective to reveal the mechanism of NO2--N oxidation, optimize the process of nitrogen removal from wastewater and further control water eutrophication.
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