Kinetics of Arsenite Oxidation by Chemoautotrophic Thiomonas arsenivorans Strain b6 in a Continuous Stirred Tank Reactor

As(III) oxidation by a chemoautotrophic bacterium, Thiomonas arsenivorans strain b6, was evaluated in a continuous stirred tank reactor (CSTR) under a range of influent As(III) concentrations (2,000–4,000 mg/L) and hydraulic retention times (HRTs) (21.7–74.9 h). Five steady states were obtained after the CSTR was continuously operated for 115 days with over 99% As(III) oxidized under the optimal growth conditions for strain b6 at pH 6 and $30°\text{C}$ . The culture exhibited strong resilience by recovering from an As(III) overloading of $4,847.4\pm 290.9\text{mg}/\text{day}/\text{L}$ operated at a HRT of 21.7 h. Arsenic mass balance analysis revealed that As(III) was mainly oxidized to As(V), with unaccounted arsenic well within the analytical error of measurement. The best estimates of biokinetic parameters for As(III) oxidation were obtained using the steady-state data and the Monod expression based model [ $k=5\text{mg}$ As(III)/mg dry cell weight/h; $K_s=20.1\text{mg}/\text{L}$ ; $k_d=0.008{\text{h}}^{-1}$ ; and $Y=0.011\text{mg}$ cell dry weight/mg As(III)]. The Monod model and the reactor mass balance successfully simulated both the steady-state and transient phases of CSTR operation. Sensitivity analyses defined $Y$ and $k$ to be the most sensitive to model predictions, whereas $k_d$ and $K_s$ were least sensitive to model simulations of As(III) oxidation under steady-state conditions.