Study On The Mechanism Of Enhanced Anaerobic Digestion Of Food Waste By Composite Bacterial Agent/conductive Material

Anaerobic digestion（AD）is an economic and effective technology,which can convert food waste（FW）into biogas.Strengthening anaerobic digestion is of great significance to solve the contradiction between energy and environment and realize social sustainable development.By adding compound bacteria/conductive materials（Fe-Metal-Organic Framework:Fe-MOF,Ketjen Black）to the food waste anaerobic digestion system,it was investigated that the food waste was added separately compound bacteria,conductive materials（Fe-MOF,Ketjen Black）and combined addition of composite bacteria/conductive materials,the gas production,organic matter removal rate,feed liquid characteristics and kinetic process of anaerobic digestion,and combining the electrochemical properties,functional groups and other physical and chemical properties of conductive materials（Fe-MOF,Ketjen Black）to analyze the strengthening mechanism of anaerobic digestion.Explore the application of composite bacteria and conductive materials（Fe-MOF,Ketjen Black）in the field of anaerobic digestion,and provide a theoretical basis for enhancing the performance of anaerobic digestion of food waste.The main research contents and results are as follows:（1）Five kinds of compound microbial agents were added to the anaerobic digestion system of food waste to study their effects on the cumulative biogas production,select the compound microbial agent with the largest gas production,and seek the best addition amount of the compound microbial agent in the system.Combined with the biogas production,material and liquid conditions,organic matter removal rate and other indicators,the gas production characteristics and mechanism of compound microbial agents on the anaerobic digestion of food waste were clarified from the perspective of kinetics.The results showed that in the anaerobic digestion system with 0.5 g·L^-1 of five kinds of commercial compound bacteria,the cumulative biogas production of the system with CB5compound bacteria was 4287.5 ml,which was 79.19%higher than that of the blank group;when the CB5 compound bacteria was added from 0.2 g·L^-1 to 1.0g·L^-1 the biogas production,total solids（TS）,volatile solids（VS）and chemical oxygen demand（COD）.When the addition amount was 1.0 g·L^-1,the cumulative biogas production reached the maximum value of 474.5 ml·g-VS^-1,increased by31.95%;the removal rates of TS,VS and COD increased by 45.93%,16.32%and16.24%respectively.The results of modified Gompertz model showed that the lag time of anaerobic digestion was shortened from 3.042 d to 1.397 d with the addition of CB5.The cone model simulation results showed that the hydrolysis rate constant increased from 0.096 d^-1 to 0.123 d^-1,increased by 56.25%,indicating that the addition of compound microbial agent had a significant effect on the increase of hydrolysis rate.（2）Study the effect of separately adding conductive material Fe-MOF/Ketjen Black on the biogas production,feed liquid characteristics and organic matter removal rate of anaerobic digestion of food waste.According to the physicochemical properties of the conductive material Fe-MOF/Ketjen Black,the changes in ETS activity in the digestion system and the kinetic process of gas production,the mechanism of Fe-MOF/Ketjen Black enhanced anaerobic digestion of food waste was clarified.The results show that adding an appropriate amount of Fe-MOF/Ketjen Black to the anaerobic digestion system of food waste can significantly increase the cumulative biogas production and organic matter removal rate of anaerobic digestion,and shorten the lag period.When Fe-MOF/Ketjen Black dosage was 0.5 g·L^-1 and 0.2 g·L^-1 respectively,the performance of anaerobic digestion system of food waste was the best.The cumulative biogas yield was 438.4 ml·g-VS^-1,which was 27.50%higher than that of the blank group;The cumulative biogas production of Ketjen Black was 465.5m L·g-VS^-1,which was 29.45%higher than that of the blank group;The removal rates of TS,VS and COD increased by 18.28%,40.52%and 15.31%,respectively;The removal rates of TS,VS and COD of Ketjen Black were 2.01%,6.78%and4.28%higher than those of Fe-MOF,respectively;Ketjen Black is better than Fe-MOF in strengthening the system.FT-IR analysis of Fe MOF and Ketjen Black showed that they had the same basic functional groups,namely-OH,C≡C,C=O,COO^-and C-O,which combined with NH₃ or H⁺,could reduce the concentration of ammonia nitrogen in the system,increase the p H value and buffer capacity;the Zeta potentials of Fe-MOF and Ketjen Black are 22.34 m V and-22.63 m V,respectively,which provide a good environment for establishing DIET;the conductivity is 0.1875 m S·cm^-1and 0.2493 m S·cm^-1,respectively,to provide a path for the establishment of DIET;The addition of Fe-MOF and Ketjen Black can increase the activity of ETS in anaerobic digestion system by more than 2 times,indicating that Fe-MOF and Ketjen Black have rich organic functional groups and electrochemical properties,which can provide suitable environment and faster electron exchange capacity for the growth and reproduction of microorganisms.The modified Gompertz model was used to fit the biogas production.The results showed that Fe-MOF shortened the lag period of anaerobic digestion from3.042 d to 2.006 d,by 34.06%,while Ketjen Black shortened the lag period to1.544 d,by 49.2%.The increase in biogas production,the removal rate of VS,TS and COD,and the shortening of the lag period show that the addition of Ketjen Black to enhance the anaerobic digestion performance of food waste is better than the addition of Fe-MOF;The hydrolysis rate constants of the blank group,the addition of Ketjen Black and Fe-MOF were 0.096 d^-1,0.092 d^-1 and 0.061 d^-1,respectively,indicating that the addition of Ketjen black had no obvious effect on the increase of hydrolysis rate,but the addition of Fe MOF had inhibitory effect.（3）In the anaerobic digestion system of food waste,the compound bacteria agent and Ketjen Black are jointly added.The results show that the combined addition of compound bacteria and Ketjen Black can further improve the gas production performance of anaerobic digestion of food waste,and make the degradation effect of TS,VS and COD more significant.When the compound bacterial agent and Ketjen Black are added together at 1.0 g·L^-1and 0.2 g·L^-1,respectively,the cumulative biogas production will increase from 359.6 m L·g-VS^-1 to 518.8 m L·g-VS^-1,44.27%higher than the blank group,9.29%～11.45higher than the single addition.The removal rates of VS,TS and COD were88.59%,51.64%,and 73.66%,respectively,which were increased by 29.09%,64.86%,and 26.93%compared with the blank group.The first-order kinetic model,modified Gompertz model,cone model and function transfer model were used to fit the biogas production of each experimental group.The results showed that the fitting accuracy of the modified Gompertz model and cone model were higher than 0.99.The strategy shortened the lag period from 3.042 d to 1.310 d;the hydrolysis rate constant was increased from 0.095 d^-1 to 0.133 d^-1,and the strengthening effect was more significant.