Remediation of hexavalent chromium contaminated soils by stimulating indigenous microorganisms: Optimization, community succession and applicability

Microbial remediation has become an environmental-friendly and promising remediation method for Hexavalent chromium [Cr(VI)] contaminated soils. However, it is hard for exogenous microorganisms to adapt to different contaminated soils. In this study, Cr(VI) contaminated soils were remediated by the indigenous iron reducing bacteria and Cr(VI) reducing bacteria under the stimulation of sodium lactate, ferrihydrite and humic acid. The Cr(VI) removal rates of contaminated soils with the Cr(VI) concentration of 2234.92 mg/kg reached 71.61% on the 24th day with a sodium lactate dosage of 5.80%, a ferrihydrite dosage of 2.00% and a humic acid dosage of 0.93% that obtained after the optimization of Box-Benhnken design. The total abundance of iron reducing bacteria and Cr(VI) reducing bacteria increased from 9.78% to 64.64% after the remediation. Bacillus, Salipaludibacillus, Gracilibacillus, Virgibacillus and Delftia played a critical role in the remediation. Adding the above three exogenous substances to Cr(VI) contaminated soils in other three regions still had an excellent remediation effect. When the initial Cr(VI) concentrations were no more than 1000 mg/kg, they could decrease to below 60.53 mg/kg after the remediation of 24 days. The Cr(VI) removal rate could still reach 89.49% even if the initial concentration exceeded 2000 mg/kg. Our results provide an attractive strategy to utilize indigenous microorganisms to remediate Cr(VI) contaminated soils.