The performance of nitrate-reducing Fe(II) oxidation processes under variable initial Fe/N ratios: The fate of nitrogen and iron species

• Published in: Frontiers of environmental science & engineering Vol. 15; no. 4; p. 73
• Main Authors: Cheng, Boyi, Wang, Yi, Hua, Yumei, Heal, Kate V.
• Format: Journal Article
• Language: English
• Published: Beijing Higher Education Press 01.08.2021; Springer Nature B.V
• Subjects: Aquatic environment; Denitrification; Earth and Environmental Science; Emissions; Environment; Fe minerals; Fe(II) oxidation; Fe/N ratio; Iron; N 2O emission; Nitrate reduction; Nitrates; Nitrogen; Nitrous oxide; Oxidation; Ratios; Reduction; Research Article; Wastewater treatment; Denitrification; Fe/N ratio; Fe(II) oxidation; Fe minerals; O emission; N
• ISSN: 2095-2201; 2095-221X
• DOI: 10.1007/s11783-020-1366-2

*Bacterially-mediated coupled N and Fe processes examined in incubation experiments. *NO 3 − reduction was considerably inhibited as initial Fe/N ratio increased. *The maximum production of N 2 occurred at an initial Fe/N molar ratio of 6. *Fe minerals produced at Fe/N ratios of 1-2 were mainly easily reducible oxides. The Fe/N ratio is an important control on nitrate-reducing Fe(II) oxidation processes that occur both in the aquatic environment and in wastewater treatment systems. The response of nitrate reduction, Fe oxidation, and mineral production to different initial Fe/N molar ratios in the presence of Paracoccus denitrificans was investigated in 132 h incubation experiments. A decrease in the nitrate reduction rate at 12 h occurred as the Fe/N ratio increased. Accumulated nitrite concentration at Fe/N ratios of 2-10 peaked at 12-84 h, and then decreased continuously to less than 0.1 mmol/L at the end of incubation. N 2O emission was promoted by high Fe/N ratios. Maximum production of N 2 occurred at a Fe/N ratio of 6, in parallel with the highest mole proportion of N 2 resulting from the reduction of nitrate (81.2%). XRD analysis and sequential extraction demonstrated that the main Fe minerals obtained from Fe(II) oxidation were easily reducible oxides such as ferrihydrite (at Fe/N ratios of 1-2), and easily reducible oxides and reducible oxides (at Fe/N ratios of 3-10). The results suggest that Fe/N ratio potentially plays a critical role in regulating N 2, N 2O emissions and Fe mineral formation in nitrate-reducing Fe(II) oxidation processes.