Analysis of nitrite oxidation process and nitrification performance by nitrogen and oxygen isotope fractionation effect
2022
Liu, Hong | Zeng, Wei | Zhan, Mengjia | Li, Jianmin | Fan, Zhiwei | Peng, Yongzhen
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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