The Study Of Biogas Generation Enhancement From Municipal Multi-source Organic Wastes By Anaerobic Co-digestion

With the development of social economy,the generation of municipal organic wastes was increasing year by year,which had aroused people’s attention.Food,kitchen,fruit/vegetable waste which had high organic and moisture content were the main component of municipal organic waste,which could be treated by the anaerobic digestion technology.However,when these organic wastes were digested alone,the anaerobic reaction often with low efficiency or fail due to the imbalance of nutrient.Therefore,it is urgent to develop the efficient collaborative disposal technology for the municipal organic wastes.Based on this,this paper firstly studied the biogas performance and system stability by different mixing ratios of food,kitchen,fruit/vegetable waste,and the optimal mixing rate was obtained.In order to further improve the efficiency of anaerobic digestion,magnetite and carbon nanotubes were selected as conductive materials to promote the electron transfer efficiency between microbial communities,and the optimal dosage of magnetite and carbon nanotubes was determined.Finally,the effects of magnetite and carbon nanotubes on hydrolytic acidification and methanogenic process were studied,and the effect of electron transfer capacity of inoculated sludge was analyzed by electrochemical method.The main research results of this paper were as follows:（1）The anaerobic digestion of different mixtures of food,kitchen and fruit/vegetable waste was studied.It was showed that the anaerobic digestion with three substrates had a better performance,and the optimal mixing ratio was food waste:kitchen waste:fruit/vegetable waste of 5:2:3.At this situtation,the maximum biogas and methane yield were 614.8 m L/g VS and354.51 m L/g VS,which increased by 10.42%and 27.02%compared with the mono-digestion of food waste.Anaerobic digestion with three substrates had better synergistic effect and system stability than mono-digestion and co-digestion.Microbial community analysis showed that different substrate mixtures changed the abundance and diversity of microbial in the system.The main dominant bacteria were Chloroflexi and Bacteroidetes;the dominant methanogens were Methanobacteriales（28.82-52.11%）and Methanobacterium（11.43-30.74%）in the digestion system.Anaerobic digestion with three substrates promoted the growth of Methanosaeta,the acetoclastic methanogenic pathway and methane yield were enhanced.（2）The effects of magnetite and carbon nanotubes on methane production in the anaerobic tri-digestion of food,kitchen and fruit/vegetable waste were studied.It was showed that magnetite and carbon nanotubes increased the cumulative methane production.The maximum cumulative methane production in magnetite and carbon nanotubes groups were 592.56m L/g VS and 622.27 m L/g VS,respectively,which were 31.97%and 38.58%higher than that in the control of 449.02 m L/g VS.Compared with the control,magnetite and carbon nanotubes accelerated the degradation of acetic acid,propionic acid and butyric acid,promoted the secretion of EPS,and increased the maximum dehydrogenase activity.Microbial analysis showed that Chloroflexi（15.13-27.66%）,Firmicutes（9.44-24.77%）and Actinobacteria（16.4-26.78%）were the main dominant bacteria.Methanobacteriales and Methanobacterium,which as the hydrogen-trophic methanogens,played an important role in the interspecific H₂ electron transport pathway（IIET）,were dominant.Compared with the control,Methanosaeta and Methanosarcina,which could involve in direct interspecific electron transfer（DIET）,enriched in magnetite groups;carbon nanotubes promoted the growth of Methanosaeta,and increased methane production by promoting the DIET pathway.（3）The effects of magnetite and carbon nanotubes on hydrolytic acidification and methanogenic process were studied.It was showed that magnetite and carbon nanotubes had no obvious effects on carbohydrate,protein,SCOD and VFAs in the hydrolysis and acidification stage of food,kitchen,fruit/vegetable waste（P>0.05）.Methanogenic process showed that the addition of magnetite and carbon nanotubes increased methane yield by 18.16%and 14.89%,respectively.Magnetite and carbon nanotubes accelerated the degradation of VFAs,relieved the accumulation of ammonia nitrogen,and the activity of the maximum coenzyme F₄₂₀increased by 36.05%and 31.55%,respectively.The results of electrochemical analysis showed that magnetite and carbon nanotubes increased the peak current of CV and redox activity of the inoculated sludge.The electron-donating capacity of inoculated sludge in control,magnetite and carbon nanotube group were 54.97,66.83 and 69.49μmol e^-/g VS;and the electron-accepting capacity were 67.25,83.13 and 76.59μmol e^-/g VS,respectively.The results showed that magnetite and carbon nanotubes mainly affect the methanogenic process,improving the electron transfer capacity of the inoculated sludge and the methane production yield.