Process Optimization And Microbial Community Change Of Rumen Fluid Fermentation Of Corn Stover

The increasing shortage of fossil energy and a series of environmental pollution problems caused by the utilization have made biomass energy get more and more concern.As kind of agricultural waste,corn stover have become the main raw material for the production of biomass energy due to its easy availability and large output.Corn stover is mainly composed of cellulose,hemicellulose,and lignin.Their complex structure severely restricted the utilization of corn stover.It is important to enhance the degradation of cirn stover for bioenergy production.Ruminants can efficiently degrade lignocellulosic biomass due to the rich rumen microorganisms in their rumen.In this study,rumen fluid was applied in the fermentation of corn stover to explore the effect and mechanisms of rumen fluid fermentation with different solid content,and multistage rumen fluid fermentation was use to improve VFA production and corn stover degradation.The fermentation effect and microbial community changes with rumen fluid ferment as inoculum during in vitro rumen fluid fermentation was studied.In addition,the fermented fulid and fermented solid was used as inoculum during the fermentation of corn stover in order to make full use of the efficient microbial community in the rumen fluid.Corn stover with different substrate concentrations were adopted for rumen fluid fermentation to study the fermentation effect and mechanism.The results show that rumen fluid fermentation can be applied to the fermentation of high solid content corn stover.The concentration of VFA produced by 10%(w/v)solid content corn stover reached 13271 mg/L.The changes of cellulase activity during fermentation showed that cellulase first adsorbed on the substrate during the fermentation to promote the degradation of the substrate.However,when the solid content is high,the p H decreasing of the fermentation system and the VFA accumulation will cause enzymatic activity inhibition.The structure of the corn stover changed significantly after the rumen fluid fermentation,the crystallinity decreased and the specific surface area increased.The result of FTIR spectrum showed that hemicellulose was mainly degraded.Multistage rumen fluid fermentation of corn stover was conducted to improve the degradation degree of corn stover and simulate rumination process,the results showed that although the fermentation effect is best in first fermentation(Stage 1),multistage rumen fluid fermentation can significantly improve the degradation degree of corn stover,especially can promote the degradation of corn stover with high solid content(10%(w/v)).After the rumen liquid fermentation of Stage 2 and Stage 3,the fermentation effect of Stage 4 has been improved.In Stage 4,the VFA produced by 10%(w/v)solid content corn stover increased from less than 1000 mg/L in Stage 3 to 5710.5 mg/L.Compared with single-stage fermentation,the degradation of corn stover by multistage rumen fluid fermentation increased by 82%.Through the study of the distribution of cellulase in the liquid phase and solid phase during the multistage rumen fluid fermentation,it was found that in Stage 1,the cellulase activity adsorbed in the solid phase was higher than that in the liquid phase,but in the other three fermentation stages,the enzymes absorbed in the solid phase is similar to that in the liquid phase,further indicating that the efficient hydrolysis of corn stover by cellulase is closely related to its adsorption on the substrate.The structure of corn stover has undergone major changes in multistage fermentation.Hemicellulose was mainly degraded in Stage 1,while multistage fermentation promoted cellulose degradationThe fermentation of corn stover was carried out using the ferment as inoculum to study the activity changes of rumen microorganisms during in vitro fermentation,and the community succession of rumen microorganisms during the in vitro rumen fluid fermentation was studied.The results showed that with the ferment as inoculum,the fermentation capacity of the microorganisms gradually decreased,and their abundance and diversity also decreased.Among the rumen bacteria,the relative abundance of Prevotella increases from F2 during the rumen fluid fermentation process,and becomes the main dominant bacteria.However,Ruminococcus significantly reduces or disappears.Through cluster analysis,it was found that from the fourth fermentation,the microbial diversity in the system began to show significant differences compared with the original rumen fluid;from the fifth fermentation,the microbial community structure gradually stabilized.The microbial distribution in the fermented liquid phase and solid phase of the corn stover was studied after rumen fluid fermentation,and it was found that the microbial community abundance and diversity in the fermentation liquid phase were slightly higher than the fermented solid phase.The fermented liquid phase was treated with p H adjustment,ruminal microbe separation,mixed with fresh rumen liquid,etc.as anaerobic fermentation inoculum to ferment corn stover.And the 10%,20%,30% fermented solid phase was used as fermentation inoculum of corn stover,thus to study the fermentation effect of fermented liquid phase and fermented solid phase.The results showed that the p H adjusted to neutral fermented liquid phase and 30% fermented solid phase as inoculum had better fermentation effect,and the SCOD concentration produced by corn stover fermentation was 14819 mg/L and 12592 mg/L,respectively,the VFA concentration were 4790.25 mg/L and 5503.49 mg/L,respectively,which was comparable to the fermentation capacity of fresh rumen fluid.Fermented liquid phase and fermented solid phase were used as inoculums respectively for corn stover fermentation,and relative abundance of Bacillus in the system with p H adjusted fermented liquid phase as inoculum was relatively high,while in the system with 30% fermented solid phase as inoculum,the relative abundance of Prevotella was relatively high.Both the fermented liquid phase and the fermented solid phase can be reutilized as fermentation inoculums,but they have a greater impact on the composition of the microbial community.