Enhancing Anaerobic Digestion Of Kitchen Wastes Via Combining Ethanol-type Fermentation With Magnetite And Humic Acid

In recent years,the output of food waste is increasing gradually,which seriously affects people’s living environment because of its easy acidification.Magnetite is a common mineral that is rich in soil and sediment,which has been widely proved to promote anaerobic digestion of organic wastes.However,the mechanism for promoting interspecies electron transfer by magnetite is still unclear.(1)In this study,the combination of magnetite and ethanol-type fermentation was used for the first time to accelerate and stabilize anaerobic digestion.The two-phase anaerobic system was used to investigate whether magnetite could delay the acidification of kitchen wastes and accelerate the efficiency of electron transfer.The results showed that magnetite stimulated the secretion of extracellular polymeric substances(EPS)of the sludge.The three-dimensional excitation emission matrix analysis showed that the content of humic acid in EPS of the sludge secreted in the presence of magnetite was the highest.Electrochemical analysis showed that the EPS secreted from the sludge in the presence of magnetite had a higher ability to donate and accept electrons.Syntrophomonas transfers electrons to Methanospirillum and Methanobacterium through direct interspecific electron transfer(DIET).Under the solid retention time(SRT)of 30 d,the methane production rate only slightly declined to 18 ± 0.8 m L/g-VSS/d in the magnetite-supplemented digester,whereas almost no methane was detected in the digester without magnetite.(2)Based on above experiments,this study continued to explore whether humic acid could delay the acidification of food waste and improve the efficiency of electron transfer in the two-phase anaerobic reaction system under the condition of ethanol-type fermentation.The results showed that when SRT was decreased from 30 days to 10 days,the activity of methane production increased after adding humic acid,with an average methane production rate increased by 27.2%.In the humic-added methanogenic digester,the electron transfer was realized by DIET between Enterococcus and Methanosarcina,and the stability of anaerobic system of kitchen wastes was improved.In addition,DIET between Geobacter and Methanothrix/Methanosarcina was also the main reason for maintaining the stability of anaerobic digestion system.