Research On The Efficacy And Mechanism Of Methane Production From Granular Activated Carbon Enhanced Anaerobic Digestion Of Fat Oil And Grease

Synergistic bacteria in anaerobic systems are more efficient than traditional hydrogendominated and formic acid-dominated electron transport through direct electron transport between species(DIET).The addition of carbon-based conductive materials such as granular activated carbon(GAC)during the anaerobic digestion of grease and grease can stimulate the DIET and increase methane production.Previous studies mainly focus on the conductivity and addition dose of GAC to optimize the GEC-excited DIET to improve the conversion rate of oil to methane,however,the adsorption properties of GAC(including the attachment of microorganisms and the adsorption of long-chain fatty acids(LCFAs,intermediate products of anaerobic digestion of fat,oil and grease(FOG))on the surface of GAC have rarely been reported,and the mechanism of influence has not been clarified.Therefore,in this study,the effect and mechanism of GAC adsorption performance on the excitation of DIET and enhanced oil conversion to methane were explored by changing the particle size,community composition and GAC dosing method of granular sludge in the inoculum under the condition that the GAC dosage was fixed.The results are as follows:(1)Different particle sizes of inoculants(S and L types)would affect the adsorption of LCFAs on the GAC surface,thus affecting the adhesion of microorganisms capable of participating in DIET on the GAC surface,resulting in a 57% and 10% reduction in methane production using S-type and L-type inoculants,respectively.(2)When the community composition of inoculants was different,the microbial composition on the GAC surface changed significantly.The domesticated inoculants stimulated DIET more,and the methane production increased by 31% compared with the undomesticated group.(3)When GAC was added in different order,microbial preattachment to GAC was better than LCFAs first adsorbed on GAC to play a role in GAC stimulating DIET,especially for unsaturated fatty acids(such as C18:1),which could increase methane production by 5.6 times.Combining the above three influencing factors,GAC was pre-mixed with the acclimated inoculants containing large particles,and then the reaction of anaerobic digestion of oil could obtain the maximum methane increase(66%)in the shortest time.The results of microbial community analysis showed that in the optimal case,the presence of GAC enriched a large number of conductive microorganisms,and the methanogenesis pathway in GAC and suspended sludge also changed.The results of this study provide a scientific basis for the design and optimization of the process of enhancing the anaerobic digestion of oil methane production by adding GAC.