Study On The Mechanisms Of Applied Voltage Assisted Anaerobic Digestion To Improve Methane Production With Protein

In 2019,the output of wet sludge from China’s urban sewage treatment plants was as high as 46.46 million tons,and the annual output of dry weight of crop straw generated by agricultural production process reached 900 million tons,which was equivalent to 23 million tons of standard oil from the perspective of energy balance.Anaerobic digestion technology can recover valuable resources from waste biomass such as sludge,but it has disadvantages such as long residence time and low energy conversion efficiency.However,limited electron transfer process is an important factor leading to low energy conversion rate in anaerobic digestion.Some researchers have found that bioelectrochemical system(MEC-AD)can enhance electron transfer in anaerobic digestion of waste biomass and improve energy conversion efficiency,but the mechanism is still unclear.Hydrolyzed with excess sludge,straw and other complex waste biomass to the substrate,the organic component is complex,and the dynamic process of release and organic matter degradation is not convenient to mechanism analysis,and protein in all kinds of waste biomass occupies a high proportion,so this topic around outside voltage driver before and after electron transfer process and functional bacteria metabolic changes in the law,with bovine serum albumin(BSA)simulation of sludge protein components,first of all,plus the drive voltage(0.6 V)of different concentrations of protein after anaerobic digestion improved efficiency,to explore the voltage of the main stages of in the reinforcement of anaerobic digestion;After second external voltage driving changes in community composition and function of bacterial flora succession is analyzed,finally,by external Electron Transfer balance reveal Direct Interspecies Electron Transferof methanogenesis contribution ratio,combined with thermodynamic analysis and theoretical model of DIET,mechanism of MEC-AD effectiveness of methane ascension parsing.By comparing the methane production efficiency of proteins with different concentrations before and after applying external voltage,it was found that MEC-AD could not change the total amount of methane production in the anaerobic digestion of proteins without rancidity,but could effectively improve the methane production rate,which increased by 45.6% under the condition of 5 g/L BSA as substrate.Under the condition of high concentration protein(15 g/L)as substrate,MEC-AD could effectively reduce the accumulation of volatile acid in the reactor,acetic acid and propionic acid decreased by 64.9% and 60.6%,respectively,and methane production increased by 225%.However,the degradation rate of volatile acid was significantly increased.When 800 mg/L and 5 g/LBSA were used as substrates,the utilization rate of volatile acid was increased by 42.8% and 78.9%,respectively.Llumina Miseq high-throughput sequencing results showed that after external voltage drive,the diversity of yin-yang polar community decreased and the difference increased significantly.After being driven by external voltage,the anode was helpful for the directional enrichment of fermentation bacteria,and the average abundance increased by 46%;the cathode was helpful for the directional enrichment of methanogenic bacteria,and the average abundance increased by 406.9%.After being driven by external voltage,the abundance percentage of Methanobacterium in the cathode increased from 10.4% to 84.3%,and the pathway of methanogenesis in the cathode changed from eosinophilic to hydrotropic.The electronic balance calculation results of external circuit showed that MEC-AD transmitted methane production through external circuit was 96.05 m L,accounting for 10% of the total gas production.The average methane production rate of MEC after deduction of the theoretical methane production of DIET pathway was still 2.3 times that of AD reactor.The enhancement of MIET pathway after electric stimulation was the main factor for the increase of MEC-AD anaerobic digestion rate.Through thermodynamic analysis,it was found that the cathode potential could be reduced to about-0.9V after the external voltage was driven,reaching the potential required for the metabolism of the hydrophobic methanogens.Hydrogen under this condition,nutritional delta G0(CH4)=-135 k J/mol,acetic acid nutritional delta G0(CH4)=-33 k J/mol,hydrogen metabolism of nutrient methane-producing gibbs free energy is more negative,reaction type priority than addicted to acetic acid metabolism,or methanogenesis process by acetic acid nutrient to make system capacity is more efficient,the hydrogen nutrient transformation of metabolic rate faster,promoted MIET ways of methane production rate.Second,compared with H+,Fd,F420 and Co B-S-S-Co M standard electrode potential is higher,stronger electronic ability,outside the applied voltage,the existence of external circuit through message pathway,electronic enter the intracellular or from three nodes to participate in the metabolic process of methane production,bypass hydrogen production process,to overcome the system of hydrogen mass transfer resistance of restrictions,accelerate the electron transfer rate.