Investigation on the effect of Cu2+, Mn2+ and Fe3+ on biotreatment of Cr(VI) by Shewanella oneidensis and Bacillus subtilis in bimetallic system

Coexistence of chromium and iron, manganese and copper in industries is common, which may affect the microbial treating efficiency and toxicity to microorganisms, thus restricting the application of microbial treatment technology. In this research, Cu2+ promoted the reduction of Cr(VI) and the fixation of total chromium in bimetallic systems for both Shewanella oneidensis MR-1 and Bacillus subtilis, while Mn2+ and Fe3+ exhibited inhibition effects. Generally, groups with coexisting heavy metal of 0.1 mM were most affected, no matter promotive or inhibitive. Toxicity analysis revealed that high concentration of heavy metal ions led to damage to the cell membranes and reduction of their survival rate. To clarify the optimal condition for microbial treatment, response surface methodology was used to investigate the influencing factors of Cr(VI) reduction by S. oneidensis. The total chromium concentration in the supernatant was correlated with three factors, and the significant order of influence was: culture time > culture temperature > pH.