Nitrogen removal performance of sulfur autotrophic denitrification under different S2O32- additions using isotopic fractionation of nitrogen and oxygen

The dual isotope fractionation of nitrogen (N) and oxygen (O) is an effective way to track the transformation of NO3--N in biological denitrification process. The Sulfur autotrophic denitrification combined with the different concentrations of S2O32- was investigated using the dual isotope fractionation of nitrogen (N) and oxygen (O) to reveal the nitrogen removal mechanism of the activated sludge. Based on successful autotrophic denitrification incubation, the modified Logistic model responded to the short-term effects of S2O32- addition on NO3--N removal and SO42- generation. Under the S2O32- addition of 0.5, 1, 2 and 4 times of the incubation stage (49.29 mg/L-394.32 mg/L), the fractionation effect of N in NO3--N ((15)epsilon(NO3)) decreased from 8.74 +/- 1.81 parts per thousand to 2.08 +/- 0.06 parts per thousand, and the fractionation effect of O in NO3--N ((18)epsilon(NO3)) declined from 11.34 +/- 0.46 parts per thousand to 5.48 +/- 0.46 parts per thousand. The (15)epsilon(NO3)/(18)epsilon(NO3) was maintained at 0.46-0.94, indicating a negative correlation between addition amount and isotope effect, and the addition of high concentrations of S2O32- was not suitable for system stabilization. Moreover, the O-18-labeled H2O (delta O-18(H2O)) tests significantly proved the presence of O exchange between NO2--N/NO3--N and H2O (67%/97%) during the nitrogen removal process, while the reoxidation of NO2--N was explored in the autotrophic denitrification. The kinetic models coupled with isotope fractionation effectively revealed the nitrogen removal characteristics in the autotrophic denitrification systems, and verified the difference between the activated sludge-based wastewater treatment process and the natural ecosystem. (C) 2021 Elsevier B.V. All rights reserved.