Promising biological conversion of lignocellulosic biomass to renewable energy with rumen microorganisms: A comprehensive review

Lignocellulosic biomass is one of the most abundant renewable resources, and their transformation into bioenergy is an effective approach to alleviate energy shortage and recycle organic wastes. This review summarized the rumen microorganisms and related enzymes, and rumen digestion strategies and mechanisms for improvement of anaerobic rumen digestion in engineering application. Main related literatures were searched on sciencedirect and web of science, systematically summarized, compared and analyzed. Rumen microorganisms accomplish the hydrolysis, acidogenisis and methanogenesis of lignocellulosic biomass, which mainly depends on the synergy of micro-organisms and enzymes. Rumen bacteria are the main players and anaerobic fungi play an indispensable role in the hydrolysis and acidogenesis of lignocelluloses. The interaction of different microorganisms promotes the efficiency of lignocelluloses conversion to renewable energy in rumen digestion system, especially protozoa and methanogens. Rumen microorganisms secrete the cellulases, hemicellulases and figninases, which have their own unique structure and action mode and synergistically promote the lignocellulose degradation. Anaerobic digestion reactor cannot be simply designed through simulating the rumen structure and environment, while the simulation of rumen digestion strategies according to the physicochemical properties and microbial community is more important. The substrate structure and additives significantly improve the rumen digestion of lignocellulosic biomass as a potential design strategy. Finally, the current challenges, future works, and prospects on biological conversion of lignocellulose to bioenergy with rumen microorganisms are outlined.