Effect of arsanilic acid on anaerobic methanogenic process: Kinetics, inhibition and biotransformation analysis

•Methane yield was not affected by arsanilic acid at concentration <0.46 mM/L.•The IC50 of arsanilic acid to anaerobic methanogenic sludge was 0.47 mM/L.•37–59% Of the added arsanilic acid was removed after 115 days of incubation.•Arsenate was the main species at low initial arsenic acid concentration.•Arsenite was the main species at high initial arsanilic acid concentration.

Arsanilic acid (4-aminophenylarsonic acid) is widely used in the poultry and animal industries as a feed additive in the diets. Nearly all the added arsanilic acid is excreted unchanged in manure resulting in the risk of arsenic contamination. In this study, the effects of arsanilic acid on the kinetics, inhibition of methanogenic process and its biotransformation were investigated. The methane yield was not affected by arsanilic acid loading at concentration <0.46 mM, while the methane production was completely inhibited at concentration of 0.92 mM. The IC50 of arsanilic acid in this study was 0.47 mM. After 115 days of incubation, 37–59% of the added arsanilic acid was degraded. The species analysis indicated that at lower initial arsanilic acid concentration, the soluble inorganic arsenic mainly existed in the species of arsenate (As(V)), while at higher initial arsanilic acid concentration (>0.460 mM), the soluble inorganic arsenic mainly existed in the species of arsenite (As(III)), which explains why higher arsanilic acid concentration has severe inhibition to methanogens.