Modulation Effect And Enhancement Mechanism Of Fe/Mn Modified Biochar On Straw Fermentation For Hydrogen Production

In the context of"carbon peaking"and"carbon neutrality",there is an urgent need to develop renewable and clean energy.The fermentative hydrogen from waste biomass can produce clean energy and solve the environmental problems caused by the difficulty of waste biomass disposing.However,the efficiency of hydrogen production by fermentation of lignocellulosic waste biomass,represented by straw,needs to be improved.The heterogeneity and complexity of straw composition,especially the coexistence of hexoses and pentoses in straw,leads to low conversion efficiency of carbon sources in straw.The search for efficient and environmental friendly intensification strategies is of great significance for the fermentative hydrogen production using straw-based biomass.Biochar,as a carbon-rich functional material with large specific surface area,rich pore space and good redox ability,can be used as a novel functional material to enhance hydrogen production from anaerobic fermentation.However,the mechanism of biochar enhanced hydrogen production from straw fermentation has not yet been clearly reported,and its effects on the hydrogen production from straw fermentation,the constitutive relationship of hydrogen production promotion function,and the key pathways regulated by biochar are yet to be further investigated.In this study,we aimed at enhancing the fermentative hydrogen production with straw as substrate,constructing a biochar-regulated straw fermentation hydrogen production system,and investigating the behavioral characteristics and regulatory mechanisms of biochar-enhanced straw fermentation hydrogen production,with the main research contents and results as follows:The ability of straw biochar to enhance hydrogen production from pentose fermentation and alleviate the problem of CCR（carbon catabolite repression）was found.The effects of biochar prepared at different pyrolysis temperatures on the fermentative hydrogen production efficiency with mixed sugars were investigated using mixed glucose and xylose as substrates.It was found that the hydrogen production of the fermentation systems in the presence of biochar pyrolyzed at 500℃and 800℃were 1385 m L/L and1659 m L/L,respectively,which increased 4.13%and 24.69%compared with the control group,and the addition of biochar at 800℃caused the utilization percentage of xylose increased from 29.8%in the control group to 40.8%.In contrast,the hydrogen production of the fermentation system with the addition of 300°C biochar decreased by 8.31%.It was also found that more dissolved organic matter（DOM）was dissolved in the aqueous phase at 300°C biochar compared with 500°C and 800°C biochar.The effect of biochar derived DOM on the fermentation hydrogen production process was examined,and the results showed that DOM induced oxidative stress in anaerobic bacteria,while weakening the relative abundance of dominant hydrogen-producing bacteria and inhibiting the fermentation hydrogen production of the system.The ability of biochar to enhance pentose fermentation for hydrogen production was further investigated in an actual straw hydrolysate fermentation hydrogen production system.It was shown that the xylose consumption increased from 1.24 g/L to 1.46 g/L in the presence of biochar compared to the control,and 59%of xylose remained in the substrate.Construction of iron-manganese modified biochar for enhancing the fermentative hydrogen production with straw as substrate.The iron-manganese modified biochar was prepared by strengthening the function of biochar by loading iron and manganese elements.The study showed that the addition of modified biochar increased the utilization of xylose in straw hydrolysate to 94.12%,and the modified char removed more than 85%of toxic by-products（phenol,furfural and 5-hydroxymethylfurfural）from straw hydrolysate by adsorption,and increased the hydrogen production of fermentation system by 67.35%.In order to solve the problem of imbalance of carbon and nitrogen ratio of straw fermentation,a sludge-conditioned straw-sludge mixed fermentation hydrogen production system was established,and by optimizing the carbon and nitrogen ratio,the hydrogen production rate of 2 g-VS/L sludge and 8 g-VS/L straw mixed system reached155 m L/g-VS_added,which was 34%higher than the hydrogen production rate of pure straw fermentation system,and the dominant hydrogen-producing bacteria Clostridium＿IV was enriched,and proteomic analysis revealed that sludge conditioning enhanced the hydrogen-producing microbial activity,resulting in a 1.71-39.47 fold up-regulation of xylose metabolism,fatty acid synthesis,flagellin and bacterial structure-related protein expression.On this basis,an iron-manganese modified biochar regulated straw sludge mixed fermentation hydrogen production system was established to achieve efficient hydrogen production from straw.Compared with the fermentation system without biochar addition,the iron-manganese modified biochar increased the hydrogen production by63.23%to 2530 m L/L,the hydrogen percentage increased from 44%to 49.7%,the hydrogen production delay period shortened from 6.98 h to 3.52 h,and the maximum hydrogen instantaneous synthesis rate increased from 25.05 m L/（L·h）to 40.81 m L/（L·h）,and the substrate energy conversion efficiency increased from 52.23%to 70.07%.Revealing the regulatory mechanism of enhanced hydrogen production from straw fermentation by Fe/Mn-biochar.It was found that Fe/Mn-biochar could regulate the metabolic pathway of hydrogen synthesis and make the hydrogen production process tend to be more efficient in the acetate type pathway,and Fe/Mn-biochar would slowly release iron and manganese ions along with the fermentation process and maintain the ion concentration at a level suitable for hydrogen production,which helps to maintain the metabolic activity of hydrogen-producing microorganisms.The structural analysis of the bacteria community confirmed that Fe/Mn-biochar could synergistically enrich the dominant cellulose-degrading bacteria unclassified＿Ruminococcaceae（31.03%）and the efficient hydrogen-producing bacteria Clostridium＿IV（38.35%）;Proteomics analysis revealed the protein expression of rate-limiting enzymes related to key aspects of hydrogen production enhanced by Fe/Mn-biochar,including glucanase,xylanase,glucosidase and xylanase for hydrolysis of cellulose and hemicellulose,and the expression of proteins related to the above enzymes was up-regulated,and the expression of proteins related to ABC transporter protein,xylose isomerase,xylulose kinase,iron oxidation involved in reducing sugar transport and utilization was upregulated 4.2-9.65fold.Therefore,the straw fermentative hydrogen production system based on Fe/Mn-biochar regulation constructed in this study can alleviate the problem of CCR and improve the hydrogen production performance of pentose fermentation in straw,which provides a new idea and theoretical basis for promoting quality and efficiency utilization of straw-based biomass and large-scale biohydrogen production process.