Biochar-induced alterations in Acidithiobacillus ferrooxidans activity and its impact on Cd(II) and As(III) adsorption from acid mine drainage

Abstract Due to continuing mining activities, Cd(II) and As(III) contamination in acid mine drainage (AMD) has become a major environmental challenge. Currently, there is increasing focus on the use of biochar to mitigate AMD pollution. However, the impact of biochar on the process of Fe(II) oxidation by Acidithiobacillus ferrooxidans (A. ferrooxidans) in AMD systems has not been determined. In this study, we investigated the effects of introducing biochar and biochar-leachate on Fe(II) biooxidation by A. ferrooxidans and on the removal of Cd(II) and As(III) from an AMD system. The results showed that the biochar-leachate had a promoting effect on Fe(II) biooxidation by A. ferrooxidans. Conversely, biochar inhibited this process, and the inhibition increased with increasing biochar dose. Under both conditions (c(A. ferrooxidans) = 1.4 × 107 copies mL–1, m(FeSO4·7H2O):m(biochar) = 20:1; c(A. ferrooxidans) = 7.0 × 107 copies mL–1, m(FeSO4·7H2O):m(biochar) = 5:1), the biooxidation capacity of A. ferrooxidans was severely inhibited, with Fe(II) oxidation efficiency reaching a value of only ~ 20% after 84 h. The results confirmed that this inhibition might have occurred because a large fraction of the A. ferrooxidans present in the system adsorbed to the biochar, which weakened bacterial activity. In addition, mineral characterization analysis showed that the introduction of biochar changed the A. ferrooxidans biooxidation products from schwertmannite to jarosite, and the specific surface area increased after the minerals combined with biochar. Coprecipitation experiments of As(III) and Cd(II) showed that Cd(II) was adsorbed by the biochar over the first 12 h of reaction, with a removal efficiency of ~ 26%. As(III) was adsorbed by the generated schwertmannite over 24 h, with a removal efficiency of ~ 100%. These findings have positive implications for the removal of As(III) and Cd(II) from AMD. Graphical Abstract