Optimization Of Anaerobic Digestion Conditions Of Cellulose Solid Wastes And Exploration Of Acid Suppression Mechanism

Anaerobic digestion as a mature biomass conversion technology,can effectively convert cellulose waste into biomethane.However,the efficiency and system stability have always been the hotspots of research.In this text,firstly,the waste cardboard was used as substrate to optimize factors such as temperature,particle size,carbon-to-nitrogen ratio(C/N),food-to-microbe ratio(F/M),and total solids content(TS)in batch experiments,and adding biochar to improve the digestion efficiency of cardboard.Then continuous stirred tank reactor(CSTR)was used to conduct long-term high-load operation.Fe,Co,and Ni were added to explore the specific effects on the formation and conversion of volatile fatty acids(VFA),and the performance of anaerobic digestion.And the inhibitory effect of VFA accumulation on microbes were analyzed.Meanwhile,high-throughput sequencing and metagenomics technology were used to detect genomic information of microbial samples before and after VFA suppression,and comprehensive analysis of key enzyme activity-related genes of hydrolysis,acidogenesis,acetogenesis and methanogenesis was performed to determine the changes in anaerobic digestion and metabolism pathways.Finally,the VFA suppression environment was simulated to investigate the changes of the extracellular polymer(EPS)components of anaerobic sludge and various ATPase activities.The main conclusions of this study are as follows:1.The best digestion effect of the cardboard was obtained when the temperature was 35℃,the particle size of the cardboard was 2-5 mm,and the F/M was in the range of 0.5-2.When the TS was 30%and the C/N ratio was 60,the methane production decreased due to ammonia suppression;when the TS was 10%and the C/N ratio was 400,the microbial activity was reduced due to insufficient nitrogen.The addition of biochar significantly increased the maximum methane production rate(Kmax)in cardboard digestion.Compared with the control group without biochar,Kmax increased by 1.41 times.The addition of appropriate biochar was beneficial to promote the synergistic activities of microorganisms and enriched the bacteria species(Syntrophomonas,Bacteroidetes,Methanosaeta)that may participate in the electron transfer between species,and achieve the purpose of efficient cardboard digestion.2.During the long-term anaerobic digestion of cellulose,when the organic load ratiom was increased to 7.36 gCOD/L/d,the microbial hydrolysis efficiency was low,and the methane production per unit substrate was only 48 mL/gCOD/d.The addition of trace elements of iron,cobalt and nickel alleviated the decline of methane production caused by high organic load in the short term.But as the digestion continues to run,the addition of trace elements improved the activity of hydrolytic and acidifying bacteria,causing a much higher rate of hydrolysis and acidogenesis than methanogenesis,resulting in the accumulation of VFA and digestive rancidity.Methanothrix was the dominant microbial community,accounting for 31.4%and 32.1%,respectively before and after VFA suppression.Firmicutes,Acinobacteria and Thermotogae which were strong tolerant to the environment were enriched at the phylum level under the influence of VFA inhibition.At the genera level,Clostridioides showed extremely strong acid resistance,with a relative abundance increasing from 1.3%to 16.5%.3.The content of coding genes related to the conversion 2-phosphate propionyl,butyryl phosphate and acetyl phosphate as precursors to propionic acid,butyric acid and acetic acid decreased by 60.8%,79.4%and 35.0%respectively affected by VFA suppression.The metabolic pathways of acetogenotrophic and hydrogenotrophic methanogenesis were dominant.The content of coding genes related to the metabolic pathway of methanogenesis in the samples of the reactor in stable operation was much higher than the content of the samples after inhibition.4.Anaerobic microorganisms secreted more EPS to resist the inhibition caused by VFA,especially the increase of protein content;H+-K+,Ca2+-Mg2+,Na+-K+ ATPase activity showed the different trends with the change of pH,resulting in the enrichment of intracellular K+and Ca2+to maintain the balance of osmotic pressure.