Cogeneration Of Hydrogen And Methane From Cyanobacteria Biomass Fermentation

The fossil energy shortage and environmental pollution are the two biggest problems of the world today. Hydrogen as a carbon-free energy carrier can potentially replace fossil fuels in the future. Among the various hydrogen production processes, hydrogen production from renewable biomass by anaerobic fermentation is an energy-saving and environmentally friendly way. And oceanic cyanobacteria with the advantage of high light energy conversion efficiency can be fermented efficiently to produce hydrogen. In this paper, the hydrogen and methane fermentation of cyanobacteria (Arthrospira maxima as the representative) is originally proposed in the international with both the theoretical analysis and the experimental study.The effects of pH, NaCl, and NaNO3 are studied for the culture and self-fermentation hydrogen production of synechococcus Miami 43511. The results show that the synechococcus favors the condition with pH of 9.5 and low salinity (0.154mM NaCl). Adding N resource to culture medium is propitious for biomass accumulation, but it will also decrease the activity of hydrogenase.The ability of hydrogen fermentation of Arthrospira maxima has been theoretically analyzed, and the maximum energy transfer efficiency of hydrogen production only is 16.6%. Cogeneration of hydrogen and methane fermentation is processed to improve the total energy transfer efficiency and reduce the harm of wastes after fermentation. The cogeneration can dramatically increase the theoretical energy conversion efficiency to 61.9%.The A. maxima culture regulation and further hydrogen and methane fermentation are studied. With the optimization of culture cycle, illumination time and media, the carbohydrates content has been increased from 14.5% to 41.0%. Hydrogen fermented by Clostridium dominated bacteria community is increased from 21 ml/g to 58 ml/g under combined nitrate and sodium stress condition. The energy transfer efficiency reaches 24.3% after hydrogen and methane cogeneration.The hydrogen production from A. maxima biomass is further improved through bacteria domestication and enzymatic hydrolysis. A. maxima biomass is used instead of glucose as the carbon source for hydrogenogens domestication. After domestication,12 kinds of main strains are detected in the bacteria community while only 5 kinds are found before the domestication. Also the hydrogen yield is increased from 49.7ml/g to 64.3ml/g, and the maximum hydrogen production rate is enhanced from 120.4 ml/(L·h) to 198.1 ml/(L·h). The enzymatic hydrolysis for A. maxima biomass results in more monosaccharoses for the hydrogen fermentation. The hydrogen yield reaches 78.7ml/g and the maximum energy transfer efficiency for hydrogen production is 4.1%. While the soluble metabolite byproducts after hydrogen fermentation are further used to produce methane, the total energy transfer efficiency is dramatically increased to 27.7%.