Enhancing methane production in dry anaerobic digestion of ruminant manures through substrates ratio regulation for strengthened microbial interactions

This study aimed to investigate the anaerobic digestion (AD) performance of sheep manure and cow dung in wet (TS 8 %) and dry (TS 20 %) conditions with five SM/CD ratios (4:0, 3:1, 2:2, 1:3, and 0:4) using batch processes. The results demonstrated that the dry AD system with an SM/CD ratio of 1:3 (DP4) exhibited a high degradation rate of volatile fatty acids (VFAs) and maintained optimal methane (CH4) production, compared to all treatments in wet AD. High-throughput sequencing analysis revealed that DP4 promoted the relative abundance of hydrolytic bacteria (e.g., Clostridium sensu stricto), acidogens (e.g., Terrisporobacter), and syntrophic acetogens (e.g., Petrimonas). These microbial communities actively facilitated organic biodegradation, VFAs generation, and conversion. Additionally, co-occurrence network analysis showed stronger syntrophic relationships between bacteria and methanogens within the dry AD system especially in DP4 compared to the wet AD system. The symbiotic relationship, connected by the mediators, especially Petrimonas, facilitated the conversion of VFAs and H2/CO2 into CH4 through acetoclastic pathway dominated by Methanosarcina and hydrogenotrophic pathways dominated by Methanobrevibacter and Methanosphaera, respectively. This study highlights the potential of maximizing CH4 production in dry AD with specific feedstock ratio through positive microbial interactions.