Efficiency Evaluation On Performance Of Acid/methane-producing In Two-stage Anaerobic Digestion Reactor At Low Environmental Temperature

With the rapid economic development,energy shortages and environmental pollution are far more serious,gradually attracting attention of all countries.The centralized treatment of livestock poultry manure and the recycling and utilization of straw as resources can solve those severe circumstances,thus have broad development and application prospects.At present,the methane production technology by anaerobic digestion of organic waste has been applied and promoted successfully in some areas,yielding broad good technological and economic benefits.However,the commonly anaerobic fermentation technology has technical barriers:low utilization of organic waste,limit development of new technologies,and the lack of anaerobic digestion process control strategies and microbiological mechanism discussion.Especially in alpine regions,anaerobic digestion technology is difficult to promote due to the restriction of fermentation temperature.Therefore,it is urgent to develop new technologies to efficiently utilize organic waste for energy and resource utilization.This article focuses on the practical problems in the application of biogas in the cold northeast region and the theoretical problems to be studied in depth,and constructs a set of two-stage anaerobic digestion technology.It uses agricultural waste cow dung and corn stalks as raw materials,and develops a combined use of mixed substrates.Research on the characteristics of fermentation methane production.By optimizing the compatibility table,screening the ecological factors that affect the anaerobic fermentation of mixed substrates,guiding the start-up of the two-end anaerobic fermentation device,and simulating the actual working conditions of winter biogas application to investigate its operating efficiency,combining microbiological research to establish the high efficiency of anaerobic fermentation Low temperature boundary conditions of operation.Under these low temperature conditions,explore and optimize the two-stage anaerobic fermentation technology control strategy and microbial characteristics,and guide practical applications to comprehensively evaluate its efficiency.The influence of temperature,C/N ratio and other factors on the efficiency of anaerobic fermentation for methane production was investigated through the study of the efficiency of anaerobic fermentation of mixed substrates for methane production,and the design scheme of orthogonal experiment.The results showed that temperature,TS%and C/N were important factors affecting methane fermentation.The best parameters for low-temperature anaerobic fermentation of cow dung and corn stalks mixed were:T=25?,C/N=25,TS=17.6%for the integrated anaerobic digestion device;T=25?,C/N=27,TS=12%for the best acid production.As for the compound strain produced by enrichment and the domestication of low-temperature(25?)biogas fermentation,microbial flora of the 10th generation is selected to be the best methanogenic compound strain.The constructed CSTR-ACSTR,the two-stage anaerobic fermentation device was quickly started,and its operating efficiency was investigated by means of gradient cooling.The results showed that the separated and segmented control was beneficial to the stable operation of the system and parameter selection.At a medium temperature of35?,the efficiency of acid-producing fermentation for 48 d is the best,and renders higher degree of acidity and SCOD,which are 4521 mg/L and 26039 mg/L respectively;the methane-generating phase can operate efficiently and stably,the production rate of volumetric gas can reach the highest 1226 mL/L reactor·d,and VS removal rate exceeds50%.During the gradient cooling process it was found that when the temperature was25?,the acid-generating phase and the methane-generating phase could still achieve stable operation;at the temperature of 20?,the hydrolysis rate of acid-generating phase slowed down,the generation efficiency of methane dropped rapidly,the volatile acid content dropped by 29.6%with 1270 mg/L,the gas productionwas decreased by54.1%compared to that at 25?,and the maximum gas production was only 720mL.Using Miseq sequencing technology to analyze the microbial flora structure and its diversity in the stable period of CSTR-ACSTR operation,it was found that the system had the same dominant bacterial colony at 35?,30?,and 25?.The dominant bacteria colony are Clostridia,Bacteroidia and Betaproteobacteria;the dominant bacteria at 20? will mostly transition to Synergistia and Gammaproteobacteria;the dominant bacteria at 35?,30? and 25? in the methane-generating phase are mainly Methanobacterium,Methanobrevibacter,Methanoculleus and Methanospirillum,and the microbial flora structure is diverse and good.When the temperature drops to 20?,the bacterial species Methanobacterium disappears,and the relative abundances of Methanospirillum,Methanobrevibacter,and Methanoculleus are all less than 2%,and the microbial flora structure of methane-generating phase is more sensitive to low temperature.In view of the current status of methane application in northern cold regions,the control strategy and microbiological research for CSTR-ACSTR reactor at low temperature 25?were carried out.The results showed that for the acid-producing fermentation system,HRT=24 d was selected as the operating parameters,and the acid-producing phase was started with parameters of pH=7,TS%=12%,and C/N=27:1,which could render the best operating effect.The indicators of the stable phase are as follows:pH:6.37±0.6,ORP:-210 mv,VFA concentration:2520±80 mg/L,and SCOD:20000 mg/L;for the methane-generating phase,the parameters of HRT=40 d,OLR=3.0kg VS/m³·d were used as the operating parameters,the fermentation broth of the acid production system HRT=24d was used as nutrition,and the compound strain of methane fermentation was inoculated;after the methane-generating phase was started,the gas production performance was the best,and the performance during stable operation period showed that the methane production was 3743 mL/d,production rate of volumetric gas was 7831.7 mL/L_reactor·d,VS removal rate was 49.1%,and methane content accounted for 58.0±1.3%.The microbial flora structure was analyzed by Miseq high-throughput sequencing which revealed that Acinetobacter,Proteiniphilum,Pseudomonas,and Lactococcus were the dominant bacterial genera during the stable operation of the acid-producing phase,accounting for 50.8%of the total bacterial sequence;the dominant bacterial genera during the stable operation of the methane-generating phase were Synergistaceae,Peptostreptococcaceae,Christensenellaceae,Trichococcus,and Pseudomonas,accounting for 32.2%of the total bacterial sequence.At the same time,the dominant archaea genera of the methanogenic phase were Centarchaeum,Methanobacteriaceae,and Methanobacterium.To carry out practical application and comprehensive performance evaluation of CSTR-ACSTR,the results showed that the demonstration project of CSTR-ACSTR has achieved stable operation throughout the year,with good economic and ecological benefits.By using parameter control and engineering adjustment,the system is stable with strong impact resistance.The temperature of the acid-producing fermentation system in winter is 27?,the VFA concentration over 2600 mg/L,and the SCOD concentration over 18000 mg/L.The methane-generating phase is not affected by the impact and the production rate of volumetric gas is about 0.75 m³/m³·_digester·d.The methane production during stable operation in winter is about 1500 m³/d,the production rate of volumetric gas is about 0.75 m³/m³_digester d,and the VS removal rate is about 40%.The software Super Decisions 2.1 was used to evaluate the comprehensive benefits of the CSTR-ACSTR,and a basic evaluation system was constructed.The weights of authority of 16 indicators such as production rate of volumetric gas,CO₂ and SO₂emission reduction were compared.Their values were assigned through calculation and analysis.The comprehensive benefit evaluation of the CSTR-ACSTR was 4.340 whose evaluation grade is excellent,indicating that the project has good operational effects and application prospects after adjustment and control.