Study On Promoting Effect Of Conductive Materials And Pretreatment On Anaerobic Digestion Of Kitchen Waste

China’s kitchen waste is produced in large quantities and has a high organic matter content,so it is beneficial to sustainable development if it is disposed of rationally and then resourcefully.Anaerobic digestion has a wide range of applications and a high energy recovery rate.The conversion of kitchen waste into methane through the action of microorganisms can recover energy from waste and has a broad development prospect.The microorganisms are subject to environmental changes,resulting in slow methane production rates,low substrate utilisation and unstable systems during anaerobic digestion.The addition of exogenous conductive materials can promote direct interspecies electron transfer between fermenting bacteria and methanogenic bacteria,which has a positive effect on maintaining the stability of the anaerobic digestion system and improving the methane production rate.In this study,four exogenous conductive materials,namely granular activated carbon（GAC）,powdered activated carbon（PAC）,ferric oxide（Fe₃O₄）and ferric oxide（Fe₂O₃）,were added to the anaerobic digestion system to investigate the effects of different materials on anaerobic digestion,and the conditions affecting anaerobic digestion of kitchen waste were optimised by response surface methodology to compare the effects of thermal pretreatment and lipase pretreatment on improving the methanogenic performance of kitchen waste.The effect of thermal pretreatment and lipase pretreatment on improving the methane production performance of anaerobic digestion of food waste was compared,and the maximum methane production rate of anaerobic digestion of food waste was further obtained by combining pretreatment and exogenous conductive materials dosing.A sequencing batch reactor anaerobic digestion system was set up with GAC,PAC,Fe₃O₄and Fe₂O₃,and a control group was set up without the addition of exogenous materials.The methane production,system p H,SCOD,ammonia nitrogen and volatile fatty acids were measured to analyse their effects on anaerobic digestion,and the optimal exogenous conductive materials were selected.The cumulative methane production was ranked from largest to smallest in the order of PAC group>GAC group>Fe₃O₄ group>Fe₂O₃group>control group.The cumulative methane production of the PAC group reached 308 m L·g^-1VS,which was 12.41%higher than that of the control group.was higher than the other groups,ammonia nitrogen accumulation was 713 mg/L and no ammonia inhibition occurred.Microbial community analysis also showed that the addition of PAC was effective in increasing the abundance of Firmicutes,Bacteroidota and Syntrophobacteraceae,as well as the abundance of Methanosaeta.promote direct interspecific electron transfer to enhance methanogenic efficiency.The response surface methodology was applied to optimise the optimum conditions for the anaerobic digestion of kitchen waste.Firstly,a single-factor test was conducted to determine the optimum values of three important factors:solids content（TS）of 5%to 15%,inoculum ratio（IR）of 1 to 3 and PAC addition（B）of 5 g/L to 15 g/L.The results of the ANOVA showed that all three factors had significant effects on the methane production of kitchen waste.The results of ANOVA showed that all three factors had significant effects on methane production from anaerobic digestion of kitchen waste,and the significant effects were IR>PAC addition>TS.The optimum conditions were obtained:TS was 9.49%,inoculum ratio was 2.77,PAC addition was 10.87 g/L,and the maximum methane production rate of kitchen waste was347.60 m L·g^-1VS.The solubility of organic matter and gas production performance of the kitchen waste was improved by pretreatment at 90°C,120°C and 150°C for 30 min,respectively.At 150°C,the p H of the kitchen waste decreased to 6.04,the SCOD concentration increased to 43.05 g/L,the cumulative methane production was 325 m L·g^-1VS,an increase of 14.44%over the control,and the system TS and VS removal rates were 20.6%and 26.95%,respectively.Pretreatment of kitchen waste with lipase addition at 0.5 g/L,1 g/L and 1.5 g/L resulted in a cumulative methane production of 331 m L·g^-1VS at 1 g/L addition,an increase of 14.53%over the control.The system TS and VS removal rates were 22.5%and 27.59%,respectively.PAC combined with pretreatment promoted methanogenesis from kitchen waste.The cumulative methane production from PAC+150°C thermal pretreatment and PAC+0.1 g/L lipase pretreatment were 349 m L·g^-1VS and 354 m L·g^-1VS.The addition of exogenous conductive materials and pretreatment can both improve the efficiency of anaerobic digestion of kitchen waste for gas production,and the combination of the two has a further contributing effect and is important for achieving the transformation of kitchen waste into a resource.