Two-phase Pressurized Anaerobic Digestion Of Food Waste

As the world's most populous country,China produces huge amounts of food waste every year.Bioenergy recovery through anaerobic digestion(AD)process is considered to be a sustainable food waste treatment practice.At present,the methane content of biogas get by traditional anaerobic digestion was generally low(<65%).To achieve high value utilization,the biogas produced by traditional anaerobic digestion process need purification and cleanse.However,anaerobic digestion with pressure is a novel technique that can realize in-situ biogas purification,make the methane content in biogas more than 90%,and the produced biogas with a certain pressure,which makes biogas can be directly injected into the natural gas pipeline network for high value use.Therefore,the pressurized anaerobic digestion is getting more and more attention by researchers.This research firstly analyzed the physicochemical properties of five kinds of food waste as well as the biogas production potenical.Then,the optimal process-conditions of food waste anaerobic digestion for acid production were explored and a microbial enrichment experiment was prepared for two-phase pressurized anaerobic digestion.More importantly,the in-situ purification effect and the highest organic load of syetem can reach was explored using the self-developed pressurized two-phase anaerobic digestion system,which use food waste as the substrate.The main research contents and conclusions are as follows:(1)The physical and chemical properties of five different types of food waste(hot pot,fast food,Hebei cuisine and others)were analyzed,and the biogas production potencial of five different types of food waste was test through batch experiments.Results show that the five kinds of food waste have the characteristics of high water content(>70%),high VS/TS ratio(>85%),suitable C/N(14.8~26.7),high fat content(18.61%TS~30.86%TS)and high calcium content(2.74%TS~3.94%TS).And the biogas production potenical are different from each other,Hot pot shows the highest methane production potential,364.8 mL/gVS.(2)Food waste anaerobic digestion for acid production was go on with different OLR(5 g VS/L·d and 10 g VS/L·d)and different HRT(3 d and 6d).The microbial enrichment was through bio-carrier surface forming biofilm in an anaerobic digestion biofilm reactor.The results show that the best OLR of acid production of food waste is 5 g VS/L·d,HRT is 6 d.After 60 days of anaerobic digestion experiments,the dry weight of the bio-carrier increase 0.3551 g,and the number of microorganisms in one gram of microbial film is 13.64% higher than the equivalent quality of biogas slurry.(3)The two-phase pressurized anaerobic digestion system was operated under 37?.This research firstly explored the in-situ purification effect and the stability of the methane phase pressurized reactor under 0.3 MPa,0.6 MPa,1.0 MPa and 1.7 MPa.Further more,the highest OLR of the methane phase pressurized reactor can receive under the optimal purification pressure was explored.The results show that: The two-phase pressurized anaerobic digestion system runs stably under 0.3 MPa~1.7 MPa.With the pressure increase,daily methane production and COD removal rate decreased,while the methane content gradually increased.It is worth noting that after the pressure reach 1.0 MPa,the methane content do not increase significantly with the increasing pressure.The COD removel rate of the system acidogenic phase matched methanogenic phase under 0.3 MPa,0.6 MPa,1.0 MPa and 1.7 PMa are 96.53%,91%,87.69% and 86.46%,respectively.Two optimal process conditions are obtained in this study:(1)Under 0.3 MPa,methane gas loading rate is 249.4 m L/g COD,and the content of methane is 79.8±1.1%,which had the advantaged gas production;(2)Under 1.0 MPa,the biogas yield is 180 m L/g COD,the methane content was 89.4±0.8%,and the purification effect is superior.In the stage of increasing OLR,the methane production phase pressurized reactor can run stably with a maximum OLR of 5 g COD/L·d under 1.0 MPa.With the OLR increase,COD removal rate decreased gradually.