Rumen microbe fermentation of corn stalk to produce volatile fatty acids in a semi-continuous reactor

Resource utilization of corn stalk is promising to relieve the problem of energy shortage and environmental pollution. Rumen microbes can improve the hydrolysis efficiency of corn stalk to produce volatile fatty acids (VFAs) efficiently. However, long-term rumen fermentation practice has not been conducted and performances of hydrolysis and acidogenesis are still unclear. In this study, the long-term hydrolysis and acidogenesis performances and microbial succession of rumen microbes for 120 d were explored in a semi-continuous reactor using corn stalk as substrate. Results showed that an average VFA yield was 0.310 g/g substrate for 120 d fermentation. VFA concentration rapidly increased to 10.34 g/L at Day 7, then gradually decreased, and finally stabilized from Day 30. VS removal reached the highest of 58.5% at Day 7, then gradually decreased, and finally fluctuated at 43.4%-48.2%. A high VFA/SCOD ratio indicated that rumen semi-continuous reactor had a good hydrolysis and acidogenesis capacity. Diversity and abundance of rumen bacterial communities in the stable stage (after Day 30) were significantly lower than those in the initiating stage (0–5 d). Rumen microbes formed a new community composition in the stable stage, and Prevotella, Succiniclasticum, Rikenellaceae_RC9_gut_group, and Ruminococcus were the main hydrolytic bacteria and acidogens to ensure the VFA production. Meanwhile, rumen bacteria co-occurring in the stable stage was simpler than that in the initiating stage. pH decrease and VFA accumulation might be the main reason for the community change in rumen bacteria, further leading to the decrease of VFA concentration in the rumen semi-continuous reactor. These findings provide a theoretical reference for long-term fermentation of lignocellulosic biomass with rumen microbes.