Hydrogen peroxide-aged biochar mitigating greenhouse gas emissions during co-composting of swine manure with rice bran

Compared to fresh biochar, aged biochar has a more significant effect on mitigating greenhouse gas (GHG) emissions in farmland soil. However, there is a relative scarcity of research addressing this effect in aerobic composting. In this study, a co-composting of swine manure and rice bran (NBC), with the addition of fresh biochar (FBC) and hydrogen peroxide-aged biochar (ABC), was conducted to investigate the dynamic changes in physicochemical properties, microbial communities, GHG emissions and related functional genes during different periods. In comparison to NBC, FBC led to a 32 % decrease in total GHG emissions (CO₂-equiv), including a 29 % reduction in CO₂ emissions, a 45 % reduction in CH₄ emissions, and a 35 % decrease in N₂O emissions. Furthermore, ABC resulted in a 14 % decrease in GHG emission (CO₂-equiv), comprising a 47 % reduction in CH₄ emissions and a 23 % decrease in N₂O emissions compared to FBC. These findings indicated that the addition of aged biochar has a more significant impact on GHG reduction during composting. Network analyses, Mantel tests and redundancy analyses suggested that the mechanism behind the lowest GHG emissions in ABC is the reduction of the relative abundance of fungi associated with CH₄ emissions, along with the nirS and nirK genes associated with denitrification. This reduction is associated with the decreasing anaerobic zones resulting from the increased pore volume in biochar after aging. Overall, this study demonstrates that hydrogen peroxide aging enhances the GHG-reducing efficiency in biochar, and provides new insights into the development of GHG-reducing technologies in composting.