Study On Co-production Of Hydrogen And Methane By Anaerobic Fermentation Of Yellow Stored Corn Straw

As one of the main crop stalks in our country,the corn straw has the characteristics of wide source,large output,easy to collect.Because of its rich organic matter,it is used as one of the common substrates of anaerobic fermentation gas.However,the dense structure and complex composition of lignocellulose in corn straw often limit its biodegradability.Yellow storage technology can degrade some cellulose and other components in corn straw by microbial fermentation,and at the same time inhibit the metabolism of other microorganisms through the lactic acid produced to maintain the freshness of corn straw,which is usually used as the main method for storing straw feed.However,to ensure an adequate feed source for livestock and poultry,farmers often store more corn stalks,leading to a surplus.Due to the introduction of lactic acid bacteria and the addition of urea and other substances in the yellow storage process of corn straw,the biodegradable components such as hemicellulose and cellulose are partially degraded,and the polymerization degree of corn straw is reduced to a certain extent,making it more conducive to the improvement of anaerobic fermentation gas production performance.In addition,the microbial biochemical process involved in anaerobic fermentation is complex and changeable,and the microorganisms at different stages of hydrogen production and methane production in the fermentation system are easy to interfere with each other,thus producing inhibition due to the imbalance of metabolites.The hydrogen-alkane co-production technology of biomass anaerobic fermentation can separate the hydrogen-producing phase and methane-producing phase,which can significantly improve the metabolic efficiency of the two-phase microorganisms,and thus improve the conversion rate of raw materials and energy conversion efficiency.Based on this,this paper took the pre-treated sludge by boiling as the inoculation source.Firstly,the influence of different fermentation conditions on hydrogen production efficiency was investigated,and the fermentation system was acclimated and expanded under the optimal fermentation conditions to screen out the efficient hydrogen producing bacteria source suitable for corn stalk substrates.Secondly,taking different yellow storage parameters as factors,the effects of yellow storage straw and corn straw on cumulative hydrogen production,volatile fatty acid(VFAs)concentration,chemical oxygen demand(COD)content and soluble reducing sugar content were compared and analyzed,and the mechanism of influence of yellow storage parameters on hydrogen production of corn straw was revealed.Then,the anaerobic fermentation methanogenic properties of hydrogen-producing residues with different yellow storage parameters were investigated,and the mechanism of influence of hydrogen-producing residues with different basic characteristics on methanogenic properties and liquid phase metabolites was revealed.Finally,from the macroscopic and microscopic point of view,the distribution of material flow and the migration of key element-hydrogen in anaerobic fermentation hydrogen-alkane co-production process were analyzed,which provided a potential way for the green and efficient resource disposal of corn stalk biomass.The following conclusions are drawn:(1)The pre-boiled sludge was used as the source of hydrogen producing bacteria.The effects of C/N and initial p H of the system on the hydrogen production performance were explored with corn straw and fresh cow manure as substrates.The results showed that when C/N was 24 and p H 6.0,the anaerobic fermentation had the best hydrogen production effect,and the hydrogen concentration reached 40%,61.53%of the initial hydrogen production concentration.Under the optimal conditions of corn straw fermentation for hydrogen production,15 rounds of acclimation process were carried out,and eventually hydrogen production gradually rose,showing a good hydrogen production efficiency.(2)Three kinds of yellow silage straw,"common yellow silage corn Straw"(T_A group),were inoculated with optimized high-efficiency hydrogen-producing bacteria;Common yellow corn straw+5%urea(T_B group);The effects of different yellow storage parameters on hydrogen production of corn stalks were studied by using common yellow storage corn stalks+5%urea+0.5%microbial agent(T_C group)and non-yellow storage corn stalks(CK)as substrates.The results showed that the yellow storage process changed the initial environment of the system and the content of VFAs,reducing sugar,p H and COD in the fermentation process,and improved the fermentation performance of hydrogen production.The highest hydrogen yield was obtained in T_C group(38.21 m L/g VS),which was 45.39%higher than that in control group(26.28 m L/g VS).According to the cumulative hydrogen production,the order of hydrogen production effect of anaerobic fermentation in each treatment group was T_C>T_B>T_A>CK.(3)Using hydrogen-producing residues as substrate,the anaerobic fermentation properties of hydrogen-producing residues with different yellow storage parameters were further investigated.Although the modified Gompertz model showed that the lag time of anaerobic fermentation was increased in the yellow storage group,the yellow storage group showed excellent methanogenic performance,and the fitting coefficient R2 was≥0.9976.Among them,the hydrogen production residue of TC group obtained the largest cumulative methane production(52.98 m L/g VS),which was 33.41%higher than that of CK(39.71 m L/g VS).The comparison of the composition of liquid phase in the residue of methane production and hydrogen production shows that the COD removal rate of CK group is 63.44%,and that of yellow storage group is 64.06-65.35%.Taking the total gas production as the evaluation index,the total gas production of hydrogen and methane in TC group was the highest,and the best effect in TC group may be due to the fact that the added urea provided the required nitrogen source for the reaction,which produced a large amount of VFAs in the hydrogen-producing phase and promoted the generation of hydrogen and methane at the same time.The order of comprehensive benefits in hydrogen-alkane co-production process was T_C>T_B>T_A>CK.(4)The input and output of substances in the hydrogen-alkane co-production process of anaerobic fermentation of yellow corn straw were quantified from macroscopic and microscopic perspectives,and the process related model was established.The distribution of material flow and the migration of key element-hydrogen in the process of hydrogen-alkane co-production are analyzed.The TC group with the best comprehensive benefit in hydrogen-alkane co-production process was taken as the evaluation object.The results showed that only0.7287 g of substance entered the hydrogen-rich gas after anaerobic hydrogen production of 12g of yellow stored corn straw,and 0.8068 g of biogas could be obtained for every 299.2713 g of hydrogen production residue after secondary utilization in the methane production stage.At the stage of hydrogen production,2.14%of hydrogen elements migrated to the gas phase,44.71%and 53.15%of hydrogen elements were fixed in biogas slurry and biogas residue,respectively.In the methanogenic stage,0.15%of hydrogen migrated to the gas phase,94.09%and 5.76%of hydrogen migrated to the biogas slurry and biogas residue,respectively.