Study On Enhancement Of Methane Production By Low Temperature Anaerobic Digestion With Electric Field And Biochar

The optimal temperature for stable operation of anaerobic digestion is about 35°C,and lower temperature will inhibit microbial metabolic activity,resulting in anaerobic digestion failure.China has a vast territory,the overall position in the mid-latitude range,the annual average temperature of about 10°C.At the same time,the latitude of the north and south is close to 50 degrees,the altitude difference between east and west is more than 4800 meters,and the temperature difference in different regions is large.The extremely low temperatures at these high latitudes and altitudes have seriously hindered the application of anaerobic digestion technology.In this context,this research explored the influence of different voltage parameters and biochar parameters on low-temperature anaerobic digestion by applying electric field and biochar to enhance low-temperature anaerobic digestion to produce methane,and explored its joint mechanism through the gas-liquid physicochemical properties and microbial genomics data of anaerobic digestion system,mainly studying the following:(1)Through the screening and enrichment of low temperature inoculum,cow dung was selected as the best low temperature inoculum,and the best low temperature enrichment digestion strategy was obtained.The results showed that the cumulative methane production was the highest when the voltage was applied at the low temperature enrichment stage and the low temperature anaerobic digestion stage,which was 39.64% higher than that without voltage and 134.7% higher than that without enrichment culture.Microbiological analysis showed that the applied voltage enrichment culture significantly improved the relative abundance of the methanogenic archaea(Methanomassiliicoccus,Methanocorpusculum,unclassified Methanomicrobiaceae,Methanobacterium,Methanoculleus,Methanocalculus),and cold-loving hydrolytic acidifying bacteria(unclassified Bacteroidetes,Treponema).Functional analysis showed that the combination of applied voltage and enrichment culture improved the expression of key enzyme genes in the low-temperature anaerobic digestion process,such as Acetyl-Co A ligase(EC:6.2.1.1),coenzyme-F420 oxidoreductase(EC:1.5.98.2),coenzyme M methyltransferase(EC:2.1.1.90),D-fructose-1,6-bisphosphate-1-phosphate hydrolase(EC:3.1.3.11),pyruvate: ferredoxedhorin 2-oxidoreductase(EC:1.2.7.1),etc.(2)The effects of different voltage intensities on low-temperature anaerobic digestion were investigated in the range of 0.2~1.4 V,and the optimal voltage intensity was obtained.The results show that the optimal voltage strength is 0.2V,followed by 1.0V.The cumulative methane production at 0.2V and 1.0V increased by 111.4% and 41.77%,respectively,compared with the blank group.The applied voltage helps to increase the concentration of methane and reduce the concentration of carbon dioxide.At the same time,the microbial community structure and functional expression were analyzed,and the microbial community structure showed that the applied voltage increased the relative abundance of Methanothrix,Methanoculleus,Methanocalculus and other methanogenic archaea in the digest,and the relative abundance of hydrolyzed acid-producing bacteria such as Romboutsia,Acetobacterium,Sulfurovum,and Pseudomonas.The functional expression of microorganisms showed that the applied voltage increased the expression of methanogenesis,acetic acid production,dark hydroxide and other functions,and also enhanced the expression of key enzyme genes in anaerobic digestion process,such as α amylase(EC:3.2.1.1),pyruvate dehydrogenase(EC:1.2.4.1),S-formylglutathione hydrolase(EC:3.1.2.12),and methylenetetrahydroptrexate cyclohydrolase(EC:3.5.4.27).(3)The effects of different concentrations of biochar on low-temperature anaerobic digestion were investigated with alkali-modified straw biochar,and the optimal biochar addition amount was obtained.After alkali modification,the surface roughness of biochar increased,porosity increased and particle size increased,the specific surface area increased from 19.66m2/g to 67.49m2/g,the average pore size of adsorption increased from 4.35 nm to 5.13 nm,and the total pore volume of adsorption increased from 0.021cm3/g to 0.086cm3/g.The low-temperature anaerobic digestion experiment with different biochar addition concentrations was carried out with alkali-modified biochar as an additive,and the biochar concentration was set to 1~60%.The results show that when the addition concentration of biochar is 1~5%,it has a promoting effect on low-temperature anaerobic digestion.The optimal biochar concentration was 5%,and its cumulative methane production was increased by 30.26% compared with the blank group.Excessive biochar concentration will lead to a decrease in methane content and reducing sugar concentration,while moderate biochar concentration can help improve substrate TS and VS removal rates.Microbial community analysis showed that moderate amounts of biochar were beneficial to improve microbial community diversity,as well as acetic acid methanogens(Methanothrix),hydrogentrophic methanogenic methanogens(Methanocorpusculum,Methanomassiliicoccus,Methanogenium,unclassified Methanomicrobiaceae)and some bacteria with interspecific electron transfer(Pseudomonas,Thauera).The microbial function analysis showed that the addition of an appropriate amount of biochar enhanced the expression of microbial functions such as methane production,chemohetroph,fermentation and carbohydrate degradation in the digest.At the same time,the addition of appropriate amount of biochar anagically increased the gene expression of some key enzymes in the oxygen digestion process,such as glycogen phosphorylase(EC:2.4.1.1),acetate kinase(EC:2.7.2.1),formylmethane furan dehydrogenase(EC:1.2.7.12),etc.(4)Based on the optimal voltage intensity and optimal biochar addition obtained by different voltage intensity and different biochar addition amount experiments,the effect of electric field combined with biochar on low-temperature anaerobic digestion was further explored.The results show that compared with the applied voltage or biochar alone,the electric field combined with biochar further improves the methane production by low-temperature anaerobic digestion.The final cumulative methane production at 1V-1.5g ABC reached 154.56 m L,which was 66.52% higher than that in the blank group,and 5.35% and 22.98% higher than the applied voltage and biochar alone,respectively.The combination of electric field and biochar helps to further improve the utilization rate of reduced substrates,such as raw sugar utilization,TS and VS removal rates,thereby increasing methane production.The microbial community analysis showed that electric field combined with biochar increased the relative abundance of a variety of methanogenic archaea(Methanothrix,Methanobrevibacter,Methanoculleus,Methanobacterium,Methanosarcina,Methanolobus)including acetic acid nutrition,hydrogen or formate nutrition,methyl compound nutrition,and a variety of hydrolyzed acidifying bacteria(Proteiniphilum,Luteimonas,Sulfurovum,Tissierella,Mariniphaga,Marinobacter)and electroactive bacteria(Geobacter,Desulfuromonas,Petrimonas).Microbial function analysis showed that electric field combined with biochar enhanced the expression of heterotrophic chemotrophic,hydrogen nutrient methanogenesis,methyl disproportionation methanogenesis,cellulose degradation,as well as the expression of key enzyme genes in hydrolysis acid production and methanogenesis in anaerobic digestion,such as maltose α-amylase(EC:3.2.1.133),acyl phosphatase(EC:3.6.1.7),acetate kinase(EC:2.7.2.1),methanolcobalamin methyltransferase(mta B),phosphate synthase(EC:4.4.1.19),etc.