Continuous fixation of dissolved arsenite from flooded soil by cooperating ferrihydrite with Geobacter sulfurreducens

The fixed arsenic in soil is easy to be released into the aquatic environment in the form of arsenite (As(III)) with high toxicity and mobility due to the eutrophication of environment under anaerobic conditions. However, As(III) is difficult to be fixed in situ continuously by traditional methods, especially for the most efficient fixation method by iron ores. Based on that Fe(II) could promote the fixation of As(III), this study investigated the possibility that Geobacter sulfurreducens (G. sulfurreducens) cooperates with ferrihydrite to fix released As(III) from flooded soil in a glass column continuously under anaerobic conditions. During 42 days of operation of reactors that simulated the actual flooded soil environment, the concentration of released As(III) in the reactor with adding G. sulfurreducens and ferrihydrite is always lower than that in reactors with adding ferrihydrite or no treatment. Compared with reactors without treatment, the accumulated content of released As(III) (2455.0 ± 313.1 μg) decreased by 39.4% in the reactor with adding G. sulfurreducens and ferrihydrite on the last day, while that in reactors with adding ferrihydrite only decreased by 11.6%, respectively. These were caused by the cooperation of G. sulfurreducens and ferrihydrite, which increased the relative abundance of iron-reducing microorganisms to inhibit metabolisms of As-reducing microorganisms, inhibited the quick release of As(III) from solid soil, and promoted the release of iron to accelerate the formation of stable secondary ores with As. This study could provide an environmentally friendly method to fix dissolved As(III) pollutants from soil continuously.