| Anaerobic digestion of kitch waste to produce methane not only can realize wastes's harmless and minimization,but also realize the waste's reclamation.Due to the multi-stage of anaerobic digestion and the particularity of anaerobic bacteria in difference stages,anaerobic digestion system is very sensitive to the change of environment.In this paper,take into consideration the characteristics of kitch waste(high organic content,high salinity,high lipid)and the significant role of trace emlement(Fe,Ni,Co)in anaerobic digestion,fristly,the effects of the ratio of kitchen waste and anaerobic sludge(VSkichen waste/VS sludge,K/I)on the production of methane and the microbial community were studied;scendly,with the optimal K/I,the effects of trace emlement Fe,Ni,Co and salinity on the production of methane and the microbial community were studied;at last,by adding the conductive materials(activated carbon)to promote the application of direct interspecies electron transfer(DIET)in the anaerobic digestion process to treat four different common cooking oil among kitchen waste was studied,and the corresponding changes in microbial community was analysised.The main research contents are as follows:(1)The difference of K/I on the production of metnahe and microbial community shown "Hormesis" on methane production,which mainly could be mainly attributed to the accumulation of VFAs under high K/I,especially the accumulation of acetic acid,propionic acid and n-butyric acid,which causes acid inhibition.The maximum yield was 110.78ml/g·VS at K/I of 1(1.52%H2,53.61%CH4,44.86%C02).By RTFQ-PCR and High-throughput Sequencing,the microbial community structure under different K/I was analyzed,and the results shown that the amount of methanogen increases with the increased of K/I and then decreased;Under low K/I,Methanobacterium was dominance bacteria,while Methanosarcina became into dominance bacteria under high K/I.Therefore,Methanosarcina has a certain resistance to the toxicity of the intermediate VFAs.(2)The important of the three trace elements Fe,Ni and Co on the production of methane duing anaerobic digestion process were studied.The trace elements of Fe,Ni and Co shown "Hormesis" on the methane production.And the optimal concentration of Fe,Ni and Co were 2,0.22 and 0.2mg/L,respectively;while the methane productions were 137.5,140.1 and 162.9ml/g·VS,respectively.With the optimal K/I and the optimal concentration of each trace elements,in the semicontinuous sequencing batch reactor for 42 days,biogas accumulation at each period almost kept stable,but the methane yields obviously increased.The experimental results showed that the methane yield for Fe.Ni and Co in the sixth period increased by 18.6%,10.7%and 18.6%respectively.Thus,three trace elements Fe?Ni and Co could increase the production of methane,and Fe shown the greatest influence on methane production.Besides,RTFQ-PCR and High-throughput Sequencing technology analysised of the effect of three trace elements(Fe,Ni and Co)on the microbial community,which indicated that the three trace elements(Fe,Ni and Co)could promote the growth of methanogen.Moreover,Fe,Ni and Co have the greatest effect on Methanosarcina,which could use three methanogenic approach to produce methane.Therefore,the increased relative abundance of Methanosarcina could improve the stability of the anaerobic system and methane yield,which further suggested that Fe,Ni,Co could improve the stability of anaerobic digestion and the methane yield.(3)The effect of NaCl on the methane production during the anaerobic digestion of kitchen waste was conducted by sequencing batch with the optimal K/I.The results showed that NaCl had a "Hormesis" on methane production;when the concentration of NaCl for 4 g/L,the maximum methane yield maximum was 132.19 ml/g · VS.Then the salinity domestication was conducted by gradually increasing the concentration of NaCl.During domestication process,methane production and methane accumulation,as well as dehydrogenase and coenzyme F420,were increased with NaCl concentration and then decreased.The shift of microbial communities during domestication process were analyzed by RTFQ-PCR and High-throughput Sequencing,which shown that the amount of methanogen increased with the increasing of NaCl concentration,then become to decrease;at the intial stage,Fermicutes was the dominance bacteria,and with the increase of fermentation time and the concentration of NaCl,Euryarchaeota and Synergistetes became into dominance bacteria in the later.For Synergistetes,Methanosaeta was its main genus.Methanosaeta in S1,S2,S3,S4,S5 and S6 in relative abundance were 16.46%,17.01%,36.77%,30.39%,30.24%and 22.08%,respectively.Therefore,after domestication,the Methanosaeta showed the adaptability to the high salt environment.Moreover,the sequencing results showed that Methaosarcina also had some adaptability to the high salt environment.(4)The application of direct interspecies electron transfer(DIET)duing in the anaerobic digestion process of different common cooking oil among kitchen waste was investigated by adding the conductive materials-activated carbon.The results showed that culturing the enrichments based on activated carbon amended group could significantly improve the methane production,especially after the transfer.For the four different cooking oils(rapeseed oil,peanut oil,soybean oil and corn oil),the effect of conductive material on rapeseed oil was higher than the other three kinds of cooking oils.And in the process of anaerobic digestion of rapeseed oil,VFAs produced was only acetic acid,which concentration was highest in the control group,followed by the activated carbon group.Besides,the degradation of palmatic acid could be improved by culturing the enrichments based on activated carbon amended group.However,at the same conditons,acetic acid was only accumulated in the contral group,while there was no acetic acid produced in activated carbon amended group.Therefore,the anaerobic liquid after the domestication of the conductive material-activated carbon could promote the degradation of the palmatic acid.This study also analyzed the composition of microbial communities under different conditions through high-throughput sequencing to explained how conductive material-activated carbon could promote the degradation of grease from the microbial perspective.The results of high-throughput sequencing indicated that activated carbon could promote the growth of Syntrophomonas and Gobactor,which could conduct extracellular electron transfer to participate DIET.In addition,for Methane archaea,activated carbon could promote the growth of Methanosarcina,which had been proved an electron acceptor in DIET.Therefore,it could promote that DIET between Syntrophomonas/Geobactor and Methanosarcina in the process of anaerobic fermentation of rapeseed oil,which could improve methane production and stability of anaerobic system. |
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