This study proposes a kinetic model that accounts for the toxicity of both arsenate and arsenite and characterizes the arsenate reduction ability of a dissimilatory arsenate-reducing bacterium, Bacillus sp. SF-1 as a bioremediation agent. The model results correlated well with a series of batch reduction experiments conducted anaerobically in serum bottles with initial arsenate concentrations of 360, 735, and 1,500 mg-As/L. The reduction rate was expressed by the Haldane equation that describes the inhibitory effect of high concentrations of arsenate. The reduction rate constant k(r), half saturation constant K-S, and inhibition constant K-j were estimated respectively as 1.2 x 10(9) mg-As/cells/h, 1.5 x 10(2) mg-As/L, and 4.2 x 10(2) mg-As/L. Lethal effects of arsenite that is accumulated as the end-product of arsenate reduction were expressed by the first-order term with a lethal constant of 2.7 x 10(-4) L/mg-As/h. The yield for the bacterial cells by arsenate respiration was estimated at 4.0 x 10(8) cells/mg-As. (c) 2006 Wiley Periodicals, Inc.