The Study Of Microbial As^? Oxidation Under Aerobic And Anoxic Conditions

Microorganisms,the main drivers for the cycle of arsenic in the environment,have developed an array of mechanisms of arsenic metabolism,including arsenite oxidation,arsenate reduction,arsenic methylation and demethylation.Compared with arsenate?As^V?,arsenite(As^?)is more toxic and has a higher mobility.Thus,microbial arsenite(As^?)oxidation plays a great role in the mobilization of inorganic arsenic and remediation of arsenic contamination.In this study,a series of batch tests wrere conducted to investigate the biological arsenite oxidation by an acclimated activated sludge with various electron acceptors.The main results obtained are as follows:?1?When oxygen?O₂?,nitrate?NO₃^-?and nitrite?NO₂^-?served as the electron acceptors.The kinetic data of aerobic arsenite oxidation were fitted well with Monod kinetic model.The maximum arsenite oxidation rate and half-saturation constant were0.59 mg As g^-1 VSS min^-1 and 0.37 mg As L^-1,respectively.Kinetic results of nitrate-and nitrite-dependent arsenite oxidation were better described by the Haldane substrate inhibition model.The maximum arsenite oxidation rate,half-saturation constant and inhibition coefficient of nitrate-and nitrite-dependent arsenite oxidation were 0.40 and 0.32 mg As g^-1 VSS min^-1,0.68 and 0.15 mg As L^-1 and 116.85 and27.09 mg As L^-1,respectively.All of the types of arsenite oxidation with three different electron acceptors performed the optimal activity at near neutral pH values.Besides,the optimal temperature for oxygen-,nitrate-and nitrite-dependent arsenite oxidation was 30±1,40±1 and 20±1 ^?,respectively.?2?This study further investigated the feasibility of microbial arsenite oxidation by the acclimated activated sludge coupled with other different electron acceptors.The results showed chlorate?ClO₃^-?,chlorite?ClO₂^-?and bromate?BrO₃^-?could all serve as the alternative electron acceptors,and the reduction products of nitrate,chlorate,chlorite and bromate were nitrite?NO₂^-?,chloride?Cl^-?,chloride?Cl^-?and bromide?Br^-?,respectively.?3?According to the calculation based on the experimental results,0.26 mg-O₂,0.64 mg-NO₂^-,1.27 mg-NO₃^-,1.42 mg-ClO₂^-,0.43 mg-ClO₃^-and 0.66-mg BrO₃^-was demand for the oxidation of per mg As^? oxidation.