Revealing the ammonia oxidation process and shortcut nitrification performance using nitrogen and oxygen isotope fractionation effect

Natural abundance isotope fractionation properties have become the most effective way to explore nitrogen transformations of biological nitrogen removal from wastewater. The migration and transformation characteristics of N and O elements in the shortcut nitrification were analyzed using the N and O dual isotopic fractionation technique. The effects of dissolved oxygen (DO) and temperature changes on the performance of shortcut nitrification and isotopic fractionation were investigated. The fractionation characteristics of N and O elements during shortcut nitrification were explored by adjusting DO concentration (0.2–0.4, 1–1.2 and 3–4 mg/L) and temperature (33 ± 1 °C, 25 ± 1 °C and 18 ± 1 °C). Both δ 15 N NO2 and δ 18 O NO2 showed a gradually increasing trend with the accumulation of NO 2 − -N, and the fractionation effects induced by temperature were significantly higher than those by DO. The higher the temperature, the more significant the increase in δ 15 N NO2 ; the higher the DO, the more remarkable the increase in δ 18 O NO2, while δ 15 N NO2 : δ 18 O NO2 was maintained at 0.77–6.45. The 18 O-labeled H 2 O was successfully transferred to NO 2 − -N, and the replacement of O element was as high as 100 %, indicating that DO and H 2 O simultaneously participated in the shortcut nitrification process. The dynamic changes in isotope fractionation effects can be successfully applied to reveal the performance and mechanism of shortcut nitrification.