Effects of bacteria-loaded biochar at different pyrolysis temperatures on the immobilization of cadmium in soil

Abstract

The bioremediation of heavy metal contaminated soil has attracted significant scientific interest, though high metal concentrations inhibit microbial activity and viability. Biochar, a carbon-rich material, offers an ideal carrier for microbial immobilization due to its favorable physicochemical properties. In this study, corn straw biochar was produced at pyrolysis temperatures of 400 °C, 600 °C, and 800 °C, and two cadmium(Cd)-tolerant bacterial strains (Achromobacter xylosoxidans and Enterobacter asburiae) were selected for Cd remediation. After confirming that the composite bacteria exhibited greater Cd resistance than individual strains, the microbes were immobilized onto the biochar. The bacteria-loaded biochar was applied to Cd-contaminated soil at dosages of 0.5 %, 1 %, and 2 % (w/w), followed by a 56-day incubation. Results demonstrated that bacteria-loaded biochar enhanced Cd immobilization in the soil, with a 2 % dosage decreasing DTPA-extractable Cd by 18.2 %–38.7 %. Sequential extraction analysis revealed the substantial changes in the distribution of Cd. At the pyrolysis temperature of 600 °C and a 2 % application dosage, the content of exchangeable Cd decreased by 9.3 %, while organic matter-bound and residual fraction increased by 11.3 %. Furthermore, the bacteria-loaded biochar treatment improved soil microbial activity and metabolic capacity, increased microbial diversity, and significantly enriched the relative abundance of Cd-stabilizing microbial communities.