Silage Preservation Mechanism And Methane Fermentation Characteristics Of Maize Stalk

In China,enormous amount of crop stalks are produced every year but are not well utilized.Biological conversion of stalk into methane or lactic acid are effective ways of utilizing stalks.Silage is a commonly used way to preserve energy crops as feedstocks for biogas produciton.In this study,the effect of ensiling and aerobic deterioration on feestock storage and methane production was explored;the effect of lactic acid bacteria(LAB)on ensiling and methane production was explored;hetero-fermentative LAB communities were developed.Also the LAB communities was applied in the simultaneous saccharification and fermentation(SSF)of maize stalk.The main contents and results are as follows:(1)The changes of maize stalk composition and microbial dynamics during ensiling and aerobic exposure were investigated,and their effects on methane production and microbial community in anaerobic digestion were studied.Silage was proved to be an effective way for corn stalk storage by recovering 97.06%dry matter(DM)and 94.28%methane yield after 6 months storage.During aerobic exposure,yeasts,bacteria and lignocellulose-degrading microbes proliferate,resulting in loss of soluble material,lignocellulose degradation,and protein degradation.The secondary fermentation resulted in the consumption of soluble substances,decrease in the hydrolase activity in anaerobic digestion and decrease of specific methane yield(SMY).However,due to the activity of microbial decomposition of lignocellulose,the biodegradability of raw materials increased and thus the specific methane yield was enhanced,retarding the methane yield loss rate.Secondary fermentation caused severe DM and methane yield loss within a short time.After 9 days exposure,the DM loss and methane yield loss of silage(SEO)reached 29.29%and 40.74%respectively.After 40 days aerobic exposure,the DM loss and methane yield loss of maize stalk silage(SO)loss reached 34.11%and 52.6%,respectively.Aerobic deterioration reduced the relative abundance of Anaerolineaceae,Ruminococcaceae,Christensenellaceae and Lachnospiraceae in anaerobic fermentation.(2)The effects of different lactic acid bacteria additives including Lactobacillus buchneri(LB),Lactobacillus plantarum(LP)and Lactobacillus fermentum(LF)on corn stover silgae fermentation characteristics,aerobic stability,dry matter(DM)storage and methane production via anaerobic digestion were investigated.In the ensiling stage,inoculation of LAB additive can effectively increase the content of organic acids and improve the quality of silage.Inoculation of LB increased the DM loss of corn stalks in the ensiling stage,while inoculation of LP and LF reduced the dry matter loss.Specific methane yield increased by 0.92%(LB)and 0.05%(LP)compared with the control CK,while LP treatment decreased the SMY by 4.26%.There is a positive correlation between the methane potential of silage and the hetero-fermentative products.The total methane recovery of CK,LB,LP and LF treatements is 93.11%,94.21%,100.98%and 84.97%respectively taking the DM losse into consideration.After 10 days aerobic exposure,the methane yield recovery of CK,LB,LP and LF treamtments is 86.52%,79.56%,102.35%and 72.97%,respectively.Inoculation of LAB improved aerobic stability,reduced dry matter loss and improved methane recovery;the hetero-fermentative LAB additives(LB and LF)are more effective than homo-fermentative LAB(LP);the pentose-utilizing LAB LF is more effective than LB.(3)Hetero-fermentative LAB consortia were constructed.Hetero-fermentative LAB community SLP-1 and ASLP-2 were developed from natural fermented kimchi by continuous enrichment.Plate isolation,denaturing gradient gel electrophoresis(DGGE)and 16S rDNA clone liabrary were used to analyze the diverstity of the LAB communities.The community SLP-1 was maily composed of Lactobacillus parabuchneri(31.7%),Lactobacillus brevis(31.7%)and Lactobacillus plantarum(23.3%),Lactobacillus paracasei(6.7%),Lactobacillus pentosus(5%)and Lactobacillus mucosae(1.7%).The ASLP-2 was composed of Lactobacillus casei,Lactobacillus plantarum,Lactobacillus parabuchneri and Lactobacillus pentosus,with the proportions of 41.5%,30.8%,23.1%and 4.6%,respectively.Both SLP-1 and ASLP-2 can effectively use glucose,sucrose,arabinose and xylose.A homo-fermentative LAB community Z8 and two hetero-fermentative community Z14 and Z20 were constructed by combining different LAB strains.The Z8 consisted of Lactobacillus brevis,Lactobacillus casei and Lactobacillus plantarum;Z14 Lactobacillus buchneri,Lactobacillus brevis and Lactobacillus plantarum;Z20 Lactobacillus buchneri and Lactobacillus plantarum.(4)The effects of inoculating lactic acid bacteria community Z8,Z14,Z20,SLP-1 and ASLP-2 on corn stalk silage fermentation,aerobic stability,dry matter storage and methane production via anaerobic fermentation were investigated.SLP-1 and ASLP-2 effectively promoted the hetero-fermentation of stalk,improved acetic acid production(178.69%and 21.47%respectively),aerobic stability and dry matter recovery.Z8,Z14,Z20 both reduced acetic acid production and aerobic stability.The methane recovery of LB,Z8,Z14,Z20,SLP-1,ASLP-2 and CK treatment were 93.11%,83.99%,92.42%,94.85%,99.28%,99.17%84.97%,respectively.SLP-1,ASLP-2 obtained the highest methane recovery rate.After 10 days of aerobic exposure,the methane recovery of the treatment of LB,Z8,Z14,Z20,SLP-1,ASLP-2 and CK were 86.52%,69.80%,69.99%,63.31%,105.51%,109.87%and 72.57%,respectively.(5)The fermentation characteristics of the LAB community SLP-1 and its isolates including SLP1-1i(L.brevis),SLP-2i(L.plantarum)and SLP1-3i(L.parabuchneri)utilizing different carbon sources was compared.The utilization efficiency by SLP-1 of xylose,arabinose and cellobiose was higher than that by its isolates.The lactic acid conversion rate of SLP-1 using glucose fermentation was 0.82 g/g,which was only slightly lower than that of SLP1-2i(0.86 g/g).Simultaneous saccharification and fermentation experiments were carried out with SLP-1 and Cellulase C9748 at 30,37 and 44? respectively.The highest lactic acid yield of 0.79 g/g stalk was obtained at 30?.