| Toxic trivalent arsenite (As (III)) was oxidized by an Alcaligenes faecalis strain O1201 which was isolated from soils under aerobic condition. A batch system was employed to investigate several factors affecting As (III) oxidation, as well as the kinetics study on this strain. The cell density, As (III) concentration, pH, temperature, carbon source, and As (III) toxicity had profound effects on the rate of As (III) oxidation. The pure culture of O1201 completely oxidized As (III) to As (V) in both the exponential growth phase and the stationary phase. Kinetic studies of As (III) oxidation were performed under optimal conditions (30°C, pH 7) and citrate was a sole carbon source in batch systems. The Monod expression coupled with a logistic growth model was used to analyze the kinetics of As (III) oxidation.; Microbial As (III) oxidation was subsequently evaluated under a continuous flow condition using a continuous stirred tank reactor (CSTR). The CSTR was operated at high As (III) loadings up to 14, 593 mg/d/L. The substrate/growth/inhibition model was employed to simulate the experimental data in the CSTR. The results obtained from both model simulations and experiments indicated that complete removal of As (III) can be achieved (almost 100%), and the removal efficiency was affected by the influent As (III) level, As (III) loading, hydraulic retention time and the toxicity of As (III). In addition, the CSTR experiment revealed that the growth of strain O1201 was ceased at an As (III) concentration of 3,500 mg/L, whereas it was able to resist to the product of the oxidation (As (V)) as high as 8,000 mg/L without any growth inhibition.; The As (III) oxidation was also investigated under the continuous flow system using an immobilized-cell gel bead fluidized bed reactor (FBR). The FBR contained cells of O1201, which were entrapped inside kappa-carragenan gel beads. The reactor operation was performed at high As (III) loadings in a range of 542 to 9,985 mg/d/L. The one-dimensional diffusion reaction model was employed to simulate the experimental results. The FBR showed that complete removal of As (III) was achieved (100%), while removal efficiency was attributed to the influent As (III) level, As (III) loading, and hydraulic retention time. The study showed that the As (III) removal efficiency of the FBR was similar to that of the CSTR, but the FBR was able to operate under very low hydraulic retention time when compared to the CSTR. However, the further study is needed to improve the stability of the gel beads inside the FBR. |
