Immobilized sulfate reducing bacteria (SRB) enhanced passivation performance of biochar for Zn

The low survival rate in harsh environments has been hindering the transformation of microbial remediation technology for heavy metal-contaminated soil from laboratory to field application. Therefore, biochar was selected as the carrier in this study to immobilize the heavy metal tolerant sulfate-reducing bacteria of SRB14-2-3 for the passivation of Zn-contaminated soil. The results showed that the immobilized bacteria of IBWS14-2-3 exhibited the highest passivation performance, as the total content of bioavailable Zn fractions (exchangeable + carbonates) in soil with initial Zn concentration of 350, 750 and 1500 mg·kg−1 decreased by almost 34.2 %, 30.0 % and 22.2 % compared to the control group, respectively. In addition, the introducing of SRB14-2-3 into biochar has successfully alleviated the possible adverse effects on soil caused by the application of large amounts of biochar, while the protection of biochar against immobilized bacteria significantly improved the reproduction of SRB14-2-3, since the number of SRB14-2-3 increased by 82,278, 42 and 5 times in three different level contaminated soil. Furthermore, the new passivation mechanism for heavy metals brought by SRB14-2-3 is expected to make up for the deficiency of biochar in long-term application. And more attention should be paid on the performance of immobilized bacteria under field practical application in the future research. [Display omitted] •Biochar alleviated the toxic of Zn on sulfate-reducing bacteria.•Immobilized bacteria contained the highest passivation performance.•Immobilized bacteria introduced a new passivation mechanism into biochar.•Biochar and sulfate-reducing bacteria complement each other in function.