Abstract:[Objective] This study aims to investigate the effects of cell density and Fe(II) concentrations on the kinetics and secondary minerals during nitrate reduction and Fe(II) oxidation by Acidovorax sp. strain BoFeN1 under anoxic condition. [Methods] The anaerobic culture system containing strain BoFeN1, nitrate and Fe(II) was set up; the concentrations of nitrate, nitrite, acetate, Fe(II) were determined with the use of ion chromatography and microplate reader; and the mineralogy and morphology of the secondary minerals were characterized by using XRD and SEM. [Results] In the system of microbially-mediated nitrate (NO3-) reduction coupled with Fe(II) oxidation, high cell density substantially promoted nitrate reduction and Fe(II) oxidation. With low cell density, the Fe(II) oxidation reaction rate and extent of reaction declined for the high concentrations of Fe(II), while no obvious effect was observed in the high cell density. The higher crystallinity of secondary minerals was generated and inhibited the nitrate reduction to some extent. In the system of microbially-mediated nitrite (NO2-) reduction coupled with Fe(II) oxidation, the high cell density and Fe(II) concentration promoted the nitrite reduction, but the Fe(II) oxidation had a strong inhibitory effect on the microbial reduction of nitrite, and the types and crystallinity of secondary minerals were mainly affected by the concentration of Fe(II). [Conclusion] Biological denitrification is the main process controlling nitrate reduction; nitrite reduction was contributed by both of the biological and chemical denitrification; biological and chemical denitrification are the main reasons for Fe(II) oxidation and secondary mineral formation in the nitrate system; but chemical denitrification is the main reason for Fe(II) oxidation and secondary mineral formation in the nitrite system. This study can provide basic data and theoretical support for the coupling reactions of iron and nitrogen mediated by anaerobic microorganisms.
