Study On Characteristics And Differences Of Methane Production By Anaerobic Co-digestion Of Cow Manure And Different Crop Waste

This study was aiming at solving the problems of low and unstable methane production efficiency and easy going to acidification in the process of mono feedstock anaerobic digestion in biogas plant in China.In this paper,cow manure which was one of the main manure in livestock manure and corn straw,wheat straw,and rice straw which was the main crop stalks with large yield are selected as raw materials for anaerobic co-digestion.Also,the mono digestion of each crop stalk was carried out.The solid content(TS)of the digestion reactors were set at 10%,and feedstock to inoculum ratio was 2(TS based).All the digestion reactors were kept in temperature of 35℃ for 45 days in a constant temperature incubator.Combining to the kinetic models and microbial community structure of digestion systems,the methane production of mono and anaerobic co-digestion systems were explored.Simultaneously,the economic benefits under each co-digestion systems were analyzed according to the experimental results,so as to this can provide theoretical reference for the actual opeproportionn of biogas project.The physical and chemical indexes of methane production,pH,NH4+-N and VFAs were analyzed in the process of single straw fermentation and cow manure fermentation with three kinds of straw respectively,The characteristics of each group dynamic model were studied.The results show,The addition of cow manure in mono crop stalks anaerobic digestion system could effectively shorten the delay period,improve methane yields,and increase the buffer capacity of the system to prevent rancidity.In the anaerobic co-digestion reactors,the cow manure and corn straw ratio of 2 reactor,cow manure and wheat straw ratio of 1 and cow manure and rice straw ratio of 3 had the highest cumulative methane yields which were 272.99,167.73 and 153.22mL/g VS,respectively.The kinetic analysis of modified Gompertz model and First Order model shows that the anaerobic co-digestion of cow manure and corn straw ratio of 2 reactor had the highest methane production rate(Rmax)and the most stable pH.The anaerobic co-digestion of cow manure and rice straw ratio of 3 reactor has the short start-up time and short lag period(λ).The concentration of NH4+-N in the anaerobic co-digestion of cow manure and wheat straw system increases with the addition of cow manure.The pH value,VFAs accumulation rate and hydrolysis rate could be increased by increasing the amount of cow manure in each anaerobic co-digestion system,which was helpful to increase the buffer capacity of the system.High throughput sequencing technology was used to analyze the microbial community structure characteristics in different fermentation time systems under the optimal ratio of manure to straw,The differences of microbial community structure within and between group were studied.The results show that,In the optimal mixing ratio anaerobic co-digestion system of the cow manure and crop waste,the dominant microbial groups were the same in the digestion process.But microbial community structure in the cow manure and corn straw ratio of 2,and cow manure and rice straw ratio of 3 systems was more similar.The dominant bacterial flora at the phylum level is Bacteroidetes,Firmicutes,The dominant archaea flora is Euryarchaeota;The dominant bacteria were Petrimonas,Longilinea,Ruminofilibacter and Sedimentibacter at the genus level,The dominant flora of Archaea was Methanosarcina and Methanosaeta.But the WS6 flora also had a higher abundance in the anaerobic co-digestion of cow manure and wheat straw ratio of 1 reactor which was higher than the other two situations.It is planned to apply the test results to medium-sized biogas projects,and evaluate their economic benefits using net present value,internal rate of return,and dynamic investment payback period.The results show that,In the co-digestion system of cow manure and crop stalks,the best economic benefits were as follows:the cow manure to corn straw ratio was at 2(NPV $ 374 792),the proportion of cow manure to wheat straw was at 3(NPV $ 260147),and the proportion of cow manure to rice straw was at 3(NPV $ 359 420).When the cow manure to wheat straw ratio was 1,the resistance to risk was the worst.The resistance to risk was the best when the cow manure to corn straw ratio was 2.