Flexible biological arsenite oxidation utilizing NO_x and O₂ as alternative electron acceptors

The feasibility of flexible microbial arsenite (As^III) oxidation coupled with the reduction of different electron acceptors was investigated. The results indicated the acclimated microorganisms could oxidize As^III with oxygen, nitrate and nitrite as the alternative electron acceptors. A series of batch tests were conducted to measure the kinetic parameters of As^III oxidation and to evaluate the effects of environmental conditions including pH and temperature on the activity of biological As^III oxidation dependent on different electron acceptors. Kinetic results showed that oxygen-dependent As^III oxidation had the highest oxidation rate (0.59 mg As g^-1 VSS min^-1), followed by nitrate- (0.40 mg As g^-1 VSS min^-1) and nitrite-dependent As^III oxidation (0.32 mg As g^-1 VSS min^-1). The kinetic data of aerobic As^III oxidation were fitted well with the Monod kinetic model, while the Haldane substrate inhibition model was better applicable to describe the inhibition of anoxic As^III oxidation. Both aerobic and anoxic As^III oxidation performed the optimal activity at the near neutral pH. Besides, the optimal temperature for oxygen-, nitrate- and nitrite-dependent As^III oxidation was 30 ± 1 °C, 40 ± 1 °C and 20 ± 1 °C, respectively.