Abstract
The combination of biochar and bacteria can effectively remediate Cr(VI)-contaminated soils. However, the synergistic mechanisms remain unclear and require further investigation. In this study, we investigate the effects of a combination of biochar and Pseudomonas sp. The effects of AN-B15 on Cr(VI) transformation, soil biochemical properties, and soil microbiome are investigated, and the results show that biochar facilitated bacterial Cr(VI) removal from a solution. Specifically, the Cr(VI) removal rates by biochar are 54.44% and 42.78%, which show improvements of 14% and 20.58% by the combination of biochar and strain AN-B15 in solutions with 50 and 100 mg/L Cr(VI), respectively. Moreover, soil incubation experiments show that the bacteria-loaded biochar remediated Cr (VI)-contaminated soil more effectively than biochar or strain AN-B15 alone. Alkaline digestion shows that the amendment of 5% bacteria-loaded biochar facilitates 33.5% total soil Cr(VI) removal compared with treatment without any addition. In general, the synergistic mechanisms can be summarized as either direct or indirect immobilization. Regarding direct reduction, biochar immobilizes Cr(VI) by adsorption and abiotically reduction, which protects bacteria under the stress of Cr(VI) and enhances bacterial Cr(VI) reduction to soluble organo-Cr(III). Regarding indirect immobilization, bacteria-loaded biochar improves the soil biochemical properties, which are beneficial to Cr(VI) reduction. Moreover, bacteria-loaded biochar immobilized Cr(VI) by impacting soil bacterial communities, which increases the relative abundance of indigenous helpful bacteria to improve soil quality and reduce Cr(VI). Notably, Nocardioides is a key genus in the decline of Cr(VI) into organically integrated Cr in soil. This study deepens our understanding of the transformation of soil Cr(VI) by bacteria-loaded biochar and can contribute to the optimization of Cr(VI) remediation strategies.