Enhancement Of Methane Production From Anaerobic Fermentation Of Corn Straw By Adding Nanobubble Water

Anaerobic fermentation is regarded as an important biomass energy resource utilization technology that could convert the energy contained in the organic solid wastes into biogas for combustion or power generation and then achieve resource and energy recycling.However,there are some limiting factors in the anaerobic fermentation process of straw-based biomass for methane production such as low degree of hydrolysis and slow rate of methanogenesis.Therefore,further research needs to be investigated to improve the limiting issues in anaerobic fermentation.In this research,the effects of H₂-nanobubble water（H₂-NBW）,CO₂-NBW and（H₂+CO₂）-NBW on methane production from anaerobic fermentation of corn straw were investigated.Firstly,the optimal addition condition of NBW enhanced anaerobic fermentation was optimized based on the results of methane production.Secondly,the results of this research（NBW characteristics,microbial activity,organic matter concentration,and microbial community structure）were discussed and analyzed to explore the potential enhanced mechanism.The main conclusions of this research are as follows:（1）The effect of NBW addition on methane production during anaerobic fermentation of corn straw were investigated,and the optimal addition condition was optimized.Firstly,under the optimal condition,the enhanced effects of the three types of NBW on methane production were as follows:（H₂+CO₂）-NBW（26.96%）> H₂-NBW（24.68%）> CO₂-NBW（16.84%）.Moreover,the addition of NBW enhanced the activities of enzyme and electron transfer system（ETS）during the anaerobic fermentation process of corn straw,and promoted the generation and consumption of reducing sugar and volatile fatty acids（VFAs）.Simultaneously,the reduction rates of total solids（TS）and volatile solids（VS）in biogas slurry were also improved.The results of microbial community structure indicated that the addition of NBW enriched the hydrolysis-acidification bacteria（Anaerolineaceae,Clostridiaceae,unclassified_Bacteria,etc）and acidophilic methanogens（Methanotrichaceae or Methanomassiliicoccaceae）in the anaerobic fermentation of corn straw,thus improving the hydrolysis acidification and methanogenesis process significantly.Additionally,the metabolic functional genes favorable for anaerobic fermentation of corn straw were enhanced.（2）The enhanced mechanism of anaerobic fermentation of corn straw by the gas mass transfer characteristics of nanobubbles（NBs）was analyzed based on the results of this research.The higher gas mass transfer efficiency of NBs could improve the solubility of the gas carried in biogas slurry.（H₂+CO₂）-NBs and H₂-NBs enhanced the hydrogenotrophic methanogenesis process by providing soluble H₂+CO₂ or H₂.Furthermore,（H₂+CO₂）-NBs had a better enrichment effect on hydrogenotrophic methanogens than H₂-NBs alone.CO₂-NBs couldn’t enrich hydrogenotrophic methanogens,but improved the buffer performance of the anaerobic fermentation system of corn straw by providing soluble CO₂.The p H value of the biogas slurry could recover to the optimal p H of methanogens quickly after a decrease.（3）The potential mechanism of anaerobic fermentation of corn straw by the water mobility characteristics of NBW was analyzed based on the results of nuclear magnetic resonance spin-spin relaxation time（T₂）and microbial community structure.The higher water mobility of NBW could improve the fluidity and permeability of solution,which was beneficial to enhance the mass transfer characteristics of biogas slurry.The results of microbial metabolic function indicated that the addition of NBW enhanced the metabolic function expression of various important transport systems such as simple/multiple sugar transport system,peptide/nickel transport system,and ABC2 type transport system.Additionally,the metabolic function of transport systems mainly included permease protein,substrate-binding protein and ATP-binding protein.After the addition of NBW,the nutrient exchange with biogas slurry was accelerated by enhancing the gene expression of permease protein,and the nutrient synthesis rate and energy transfer efficiency were improved by enhancing the gene expression of substrate-binding protein and ATP-binding protein...