Co-digestion Of Switchgrass And Dairy Manure:Methane Production And The Microbial Community Characteristics

Tapping biogas industry, substituting biomethane to natural gas-transition of large and medium biogas plants from "environment-center" model to "win-win" one of producing bio-energy and degrading pollutants is imperative. Scaled production of methane needs efficient fermentation process and a variety of feedstock. Switchgrass (Panicum virgatum) is a common energy grass which could be grown on marginal land. In this study, switchgrass was considered as feedstock for methane production. Firstly, the characteristics of anaerobic digesting switchgrass were established. Secondly, Dairy manure was co-digested with switchgrass with different mixing ratios. The optimal mixing ratio and optimal dose was obtained. Thirdly, the microbial community was analyzed by clone library and quantitative polymerase chain reaction (Q-PCR). The results provided a theoretical basis and reference data for anaerobic digestion of energy grass.Batch test was conducted on switchgrass at l%-6%TS. Results showed switchgrass is a suitable feedstock for methane production. The highest methane yield171.4mL/gVS was obtained at2%TS. High dose (≥4%) of switchgrass could lead to volatile fatty acid accumulation and unstable methane production process.The methane yield obtained using different ratios of dairy manure and switchgrass as co-substrates [3:1,2:2, and1:3based on total solids (TS) content] as well as each substrate individually in anaerobic digestion for biogas production were evaluated. The highest methane yield174.9mL/gVS and155.0mL/gVS was obtained with2:2ratio at4%and6%TS respectively. The2:2methane yield was125%and74%higher than mono-digestion of manure. Positive synergistic effect was found in co-digestion of dairy manure and switchgrass. The2:2ratio achieved the most positive effect of65%(4%TS) and39%(6%TS). Therefore, the optimal mixing ratio of dairy manure and switchgrass was2:2.Batch test was conducted at4%-12%TS with2:2dairy manure to switchgrass ratio. The highest methane yield158.6mL/gVS was obtained at8%TS. The stability of switchgrass and the efficiency of switchgrass were enhanced by the co-digestion process. The2:2ratio at8%TS and a hydraulic retention time of12days was suggested in practical production.The microbial community of digesting different mixing ratio co-substrates was analyzed through clone library and Quantitative PCR. The manure to switchgrass ratio significantly influenced the content of the microbial community. Planctomycetes (28%), Chloroflexi (24%), and Bacteroidetes (24%) were the dominant phyla in digesters with a co-substrate ratio of2:2. And Fermicutes was the dominant phyla in other digesters. Methanosaeta was the dominant methanogens in all digesters.