The new strategies of using nitrogen and iron modified hydrochar to enhance methane production during co-anaerobic digestion of cow manure and corn straw

The traditional hydrochar shows limited ability to promote methane production during anaerobic digestion of organic solid waste. This study explored the effect of hydrochar modified using nitrogen and iron on methane production and microbial communities during the co-anaerobic digestion (co-AD) of cow manure and corn straw. Compared with unmodified hydrochar prepared from biogas residue (BHC), iron and nitrogen-iron modified hydrochar (BHC-Fe and BHC-N) improved the specific surface area (SSA) and proportion of oxygen-containing functional groups (OCFGs) related to direct interspecies electron transfer. The results showed that, compared to the control group (without hydrochar addition), the total methane production increased by 30 %, 36 %, and 46 % in the BHC, BHC-Fe, and BHC-N groups, respectively. The addition of modified hydrochar improved the microbial diversity and enrichment of Methanobacterium, Methanobrevibacter, and Methanosarcina spp., with BHC-N being the most effective. COD and Methanobrevibacter showed the highest explanation for methane production in AD performance indexes and archaeal genera (66.4 % and 29.3 %). Surface OCFGs of hydrochar had a more significant and direct effect on methane production than the SSA and archaeal genera. Therefore, the addition of BHC-N contributes more to promote methane production during the co-AD of cow manure and corn straw. This study could provide the new strategies for improving the co-AD of cow manure and corn straw performance, further promoting the resourcing and disposal of cow manure and corn straw.