Effect of Feedstock Concentration on Biogas Production by Inoculating Rumen Microorganisms in Biomass Solid Waste

Boosting volatile fatty acids (VFAs) production during anaerobic digestion of rich lignocellulose pulp mill excess sludge by inoculating rumen fluid and the study on the microbial community structures and functions

Hydrolysis is the rate-limiting step in the anaerobic digestion of lignocellulose. In the present study, pulp and paper mill sludge (PPMS), a lignocellulose-rich, high-volume waste, which is difficult to be treated by traditional anaerobic digestion, was inoculated with rumen microorganisms for VFAs production. The maximum extent of VFA accumulation was 3839 mg/L after 84 h in the rumen fluid-inoculated digester, versus 2338 mg/L after 96 h in the digester without rumen fluid addition. The amount was 1.64 times higher than that of digester leachate inoculum. During VFAs production, the hydrolysable of lignocellulose and extracellular polymers were promoted by inoculating rumen liquid. High-throughput sequencing results (16S rRNA genes) showed that there was a significant succession of dominant microbial community during in vitro fermentation of PPMS by rumen fluid. Fermentation by rumen fluid is a potentially effective technology to boost VFAs production from a lignocellulose-rich biomass.

Rumen microbes, enzymes, metabolisms, and application in lignocellulosic waste conversion - A comprehensive review

The rumen of ruminants is a natural anaerobic fermentation system that efficiently degrades lignocellulosic biomass and mainly depends on synergistic interactions between multiple microbes and their secreted enzymes. Ruminal microbes have been employed as biomass waste converters and are receiving increasing attention because of their degradation performance. To explore the application of ruminal microbes and their secreted enzymes in biomass waste, a comprehensive understanding of these processes is required. Based on the degradation capacity and mechanism of ruminal microbes and their secreted lignocellulose enzymes, this review concentrates on elucidating the main enzymatic strategies that ruminal microbes use for lignocellulose degradation, focusing mainly on polysaccharide metabolism-related gene loci and cellulosomes. Hydrolysis, acidification, methanogenesis, interspecific H2 transfer, and urea cycling in ruminal metabolism are also discussed. Finally, we review the research progress on the conversion of biomass waste into biofuels (bioethanol, biohydrogen, and biomethane) and value-added chemicals (organic acids) by ruminal microbes. This review aims to provide new ideas and methods for ruminal microbe and enzyme applications, biomass waste conversion, and global energy shortage alleviation.

Biotechnological potential of rumen microbiota for sustainable bioconversion of lignocellulosic waste to biofuels and value-added products

Lignocellulosic biomass is an abundant resource with untapped potential for biofuel, enzymes, and chemical production. Its complex recalcitrant structure obstructs its bioconversion into biofuels and other value-added products. For improving its bioconversion efficiency, it is important to deconstruct its complex structure. In natural systems like rumen, diverse microbial communities carry out hydrolysis, acidogenesis, acetogenesis, and methanogenesis of lignocellulosic biomass through physical penetration, synergistic and enzymatic actions enhancing lignocellulose degradation activity. This review article aims to discuss comprehensively the rumen microbial ecosystem, their interactions, enzyme production, and applications for efficient bioconversion of lignocellulosic waste to biofuels. Furthermore, meta 'omics' approaches to elucidate the structure and functions of rumen microorganisms, fermentation mechanisms, microbe-microbe interactions, and host-microbe interactions have been discussed thoroughly. Additionally, feed additives' role in improving ruminal fermentation efficiency and reducing environmental nitrogen losses has been discussed. Finally, the current status of rumen microbiota applications and future perspectives for the development of rumen mimic bioreactors for efficient bioconversion of lignocellulosic wastes to biofuels and chemicals have been highlighted.