Passivation of heavy metals during co-composting of Camellia oleifera by-products and river sediment with the additives of MnO 2-loaded biochar

Composting is not only a green and sustainable way to treat and reuse agricultural waste but also an effective method for passivating heavy metals. However, there is no research on the co-composting of the by-products of Camellia oleifera and sediment to simultaneously achieve the remediation of heavy metal and resource utilization of Camellia oleifera by-products. Moreover, MnO 2 and biochar have been widely used to promote humification in the composting process. However, few studies have investigated the efficiency of MnO 2 -loaded biochar in promoting the passivation of heavy metals in the co-composting system of Camellia oleifera by-products and sediment, and its effects on composting biological characteristics are often ignored. Therefore, this study investigated the changes in the heavy metal bioavailability and the microbial communities in sediment and Camellia oleifera by-products co-composting with the additives of MnO 2 -loaded biochar. The results showed that the MnO 2 -loaded biochar effectively passivated heavy metals and improved microbial diversity and structure, which increased the Copper and Lead residual fractions (RES-Cu and RES-Pb) by 14.01 % and 17.57 %, respectively, while the Cadmium exchangeable fraction (EXC-Cd) and the Zinc bioavailability fraction (BF-Zn) decreased by 24.72 % and 10.99 %, respectively. pH, temperature, and bacterial community were the critical regulators for heavy metals passivation by MnO 2 -loaded biochar. This study not only provides a promising resource utilization approach for Camellia oleifera by-products but also provides a new perspective and theoretical reference for the remediation of heavy metals contaminated sediment by composting.