Study On Screening Of Cold-resistant Methanogen And Its Promotion Of Straw Fermentation At Low Temperature

With the gradually shortage of the international energy supply, the energy conservation problem which had already recognized by people, have earned the increasingly attention. Methane, the environmental friendly energy for its renewable, green-based pollution-free, have already caught researchers’special cares and interests. Using the crop straw stalk anaerobic digestion to produce methane, not only could solve the energy crisis, but make the best of the resources to protect the environment, has been deemed the promising direction for the future energy development. However, in North China, low-temperature climate severely restricted the efficiency of methane fermentation. Therefore, considering the winter creates the extremely low-temperature methane fermentation environment, the investigation based on the low-temperature methane fermentation, is of critical importance.In this paper, cold-resistant methanogen that was screened and separated from diverse anaerobic environment is used to conduct this study. In addition, the study on the physiological characteristics and system taxonomic position was carried out, for the sake of exploring the influence of low temperature methane fermentation by adding the exogenous cold-resistant methanogen in this system.The results were shown as follows:(1)A cold-resistant methanogen strains, US-3, was separated from the sludge of the laboratory UASB reaction. The strains of Gram staining expresses negative, no-movement, and fluorescence microscopy and scanning electron microscopy showed regular spherical bacteria strains. The optimum substrate type was sodium formate, the optimum temperature of25oC, pH value of6.5, and Na+concentration of0.6mol/L. Strain US-3was Clostridium (Clostridium), which the sign of the zodiac as of98%.(2)A methanogen DT-6strains was separated from low temperature paddy soils. The strains of Gram staining expresses negative, no-movement, rod-shaped bacterium. The optimum substrate type sodium formate, the optimum temperature of25oC, pH value of7.5, Na+concentration of0mol/L. Strain DT-6was Citrobacter (Citrobacter), and the sign of the zodiac as of99%.(3)Comparing the#1,#2,#3(10,20,30%strain US-3was added, respectively) with the blank group, the biogas fermentation system of the method yields were all improved, and the more the additive added, the more the methane yield produced. The cumulative methane yields of the three groups tests were17186,20704,22582ml, respectively, which were20.22,33.78,39.28%higher than the blank group. The methane content average values for these four experiments (the blank,#1,#2,#3groups) were59.45,62.47,64.07,57.32%. From the above analysis, it could be concluded that the addition of the methanogenic US-3strains could consume a certain amount of organic acids, lower the pH reduced amplitude, and as a result of maintaining the system acid-base balance. In addition, the addition of the methanogenic US-3strains can improve fermentation system organic material utilization rate, reducing the COD value.(4)The cumulative methane yields of the#4.#5.#6(10,20,30%of strain DT-6) groups were14212,16056,17827ml, which were3.53,14.61,23.09%higher than the control group. The methane content average values for three group tests were58.62,59.94, and61.53%, which were all higher than the blank group of57.32%. The addition with different levels methanogenic DT-6strains could maintain the pH value differently, so that to keep the stability of the fermentation reaction. Compared with the blank group, the addition of strains would consume a certain amount of organic matter, consequently accelerated the degradation of COD.According to the overall analysis, both of the strain US-3, DT-6possessed the stimulative effect on low temperature fermentation system, while US-3strain is obviously better than the strain DT-6.