Kinetics of Competitive Reduction of Nitrate and Iron Oxides by Aeromonas hydrophila HS01

While the interaction between NO 3 − and Fe reduction is well reported, it still lacks a detailed quantitative analysis of the properties and reactions responsible for the competitive reduction. In this study, the kinetics of the reduction of NO 3 − and Fe oxides by Aeromonas hydrophila HS01 were investigated in an artificial groundwater medium. The presence of Fe oxides showed an inhibitory effect on NO 3 − reduction to a varying extent, and vice versa, which was also evidenced by cyclic voltammetry analysis of Fe(II)/Fe(III). Higher Fe(III) availability and increased Fe oxide surface areas were more favorable for Fe reduction but resulted in a stronger inhibitory effect on NO 3 − reduction. The inhibitory effect also decreased with increased hematite crystallinity. Based on the kinetics and the elementary reactions, we established a kinetic model suggesting that direct biotic NO 3 − reduction by HS01 is the leading contribution, while the cell‐associated Fe(II) produced by HS01 also reduced NO 3 − but with a limited contribution because the reaction rates of NO 3 reduction by cell‐associated Fe(II) are lower than that of NO 3 − reduction by HS01. This detailed kinetics and modeling study provides useful information for understanding the interaction between NO 3 − and Fe reduction in various subsurface environments.