Energy Production And Metabolic Characteristics Of 2-CSTRs Hydregen-Methane Production Anaerobic Digestion System

As a necessary condition for human existence,how to prooerly handle the relationship between ecological environment and energy sources is the eternal research subject in the world.The ecological environment is the foundation of human survival,development and the economic system,and the essential factors pulling the world toward a new era is energy sources.At present,energy sources mainly from natural gas,oil,coal and other non-renewable resources,and owing to the particularity of fossil fuels,its construction and production activities are possible to pollute the air,water,soil and so on,especially to pollute the local environment.Because of their high heating value,recyclability,and lack of secondary pollution,hydrogen,methane and ethanol have become alternative energy sources that have recei-ved increasing attention.Amid all the methods for producing hydrogen,methane and ethanol,biological fermentation is considered worthy of research.Biological fermentation is a traditional anaerobic fermentation technology using food waste,kitchen waste,straw as raw materials to generate hydrogen,methane and ethanol.Compared with other pathways,biological fermentation technology can not only obtained higher biogas production rate but also reduce environmental pollution.This study based on the theory of two phase anaerobic digestion,using the CSTR(Continuous stirred tank reacstor)reactor to build 2-CSTRs two-phase anaerobic fermentation system,studied the effects of a series of ecological restricting factors parameters on system efficiency and physiological methabolism characteristics.Two concepts of ethanol recovery and added enzymes are introduced into the study,and those experimental results will be helpful for the knowledge of potential capacity of the system.In the study of system operation restricting factors,the experiment discusses the establishment and operation characteristics of 2-CSTRs hydrogen-methane production system by changing pretreatment methods of sludge and C/N of influent.Research shows that the sludge pretreatment has obvious effect on reactor operate results.By contrast,acidification treatment(HyCSTR reactor sludge)-heat treatment(MeCSTR reactor sludge)(method ?)shown better stability of the system startup and operation,and higher biomass,better biological activity.Compare with the oxygen aeration(HyCSTR reactor sludge)-anoxic aeration(MeCSTR reactor sludge)(method ?),?COD of 71.9%,HPR of 16.3 L/d and MPR of 7.51 L/d of method ?,more than method ? 13.9%,31.4%,20.9%.In the aspect of effect of influent C/N ratio,the regression equations were used to elicit the effects of C/N ratios on ?? of the whole system which could be expressed as ?? = 0.0003x3-0.106x2 + 11.89x-12.379(r2=0.9903);?COD=-4E-06x3 + 0.0007x2 + 0.0525x + 23.126(r2=0.9286)in HyCSTR;?COD 5E-05x3-0.0158x2 + 1.4883x + 5.1007(r2=0.9527)in MeCSTR.Based on practical purpose,combined with the results of these equations,C/N ratio of 80 might be the better recommended option.Performance at OLR of 8-32 kgCOD/m3-d,system has 11.81molH2/kgCOD,6.67molH2/molSconsumed;11.61molCH4/kgCOD,3.97 mol CH4/molSconsumed-In the aspect of energy production,the experiments increased ethanol recovery and effluent reuse link in the 2-CSTRs system for studying the operation performance and energy production with different ethanol recovery rate(ERR).The experimental results show that,MPR was inversely proportional to ERR in MeCSTR,sludge activity tends to be stable,the quantity of sludge have obvious downward trend;When ERR was 80%and OLR for 24 kgCOD/m3·d,the system has the highest ??,but based on the consumed energy for ethanol recovery,the ERR was not the best choice to obtain high ??,ERR of 50%was the best.Recycle provided a higher ?? and energy yield than reflux,with an ethanol recovery rate of 0%and 20%,respectively.This was equal to the ethanol recovery rate of 50%,but lower than the ethanol recovery rate of 80%.This indicates that recycle would be more feasible with lower ethanol recovery rates,and reflux may be more suitable with other kinds of ethanol recovery rates.The effect of water element on the bioenergy-generation process by anaerobic fermentation and the production rate of the reactor were investigated by manually adding a mixed enzyme solution to the system.The results showed that,in a certain extent,mixed enzymes can accelerate the process,improve the efficiency and reduce the impact of surge of OLR on the system.When the OLR level was high,as the APE(adding proportion of enzymes)approached the maximum amount of additional enzyme,the increase in the magnitude of the system production rate was smaller.In continuous flow,several dosing and one-time add ways of adding enzymes,continuous flow gave the best stability and highest target products production yield;Several dosing had the mode in general similar with continuous flow,but with periodic fluctuation;One-time way caused frequent and large fluctuations.In the aspect of DLE on the system,HyCSTR presented the ethanol-type fermentation when the DLE higher than 0.67 kgCOD/g,and metabolic rate stays at a higher level in MeCSTR;HyCSTR presented the butyrate-type fermentation when the DLE was 0.5 kgCOD/g,and accumulation of valeric acid and propionic acid in MeCSTR;HyCSTR presented a atypical type fermentation when DLE was 0.4 kgCOD/g,non-dominant end products generated in HyCSTR with lower HPR.The previous studies on the physiological metabolic characteristics of each phase reactor show that,the conversion rate of the end products of each liquid phase of methane producing phase is:ethanol>valerate>butyric acid>acetic acid>propionic acid,thus,the metabolic type of the HyCSTR reactor is of great significance to the MeCSTR reactor.Acetic acid fermentation,ethanol fermentation,butyric acid fermentation and propionic acid fermentation are the four main fermenting types of hydrogen production phase,the experiment showed that when the operation parameters of temperature(35?36 ?),pH(4.5?5),HRT(6h)and DLE(0.67?2 kgCOD/g)were suitable,the HyCSTR reactor behaves as ethanol type fermentation.Ethanol and acetic acid were the main end fermented products with ethanol fermentation type.The type was stable,and high HPR and EPR can be obtained at the same time.When the HyCSTR reactor was stable for ethanol type fermentation,the MeCSTR reactor runs stably and MPR was the highest.However,during the transition period of the HyCSTR reactor metabolism type,all kinds of fatty acids accumulated in the MeCSTR reactor,and the operation stability decreased.When the HyCSTR reactor fermentation type was butyric acid fermentation type,MeCSTR reactor runs stably and MPR was high,but the conversion rate of substrate decreased,even the accumulation of propionic acid and valerate,even the accumulation of propionic acid and valeric acid appeard.