Study On Bioconversion Of Cellulose Biomass To Hydrogen

With the increasing of the world population, energy demand and consumption has increased rapidly. Facing the prominent pressure in the energy of the world, finding new energy sources has become a hotspot. Hydrogen, due to its colorless, odorless, non-toxic and produces only water after combustion, and its high energy density, the thermal value of 143 MJ/kg, is about 3 times the heat value of oil, which is considered as the ideal clean energy. Bio-hydrogen production is one of the most important methods among the whole way to explore hydrogen energy. Fermenting biomass into hydrogen is firstly the use of microorganism hydrolyzing biomass into carbohydrates, then producing hydrogen via microbial fermentation. The essence is that solar energy has been fixed in the form of biomass transformed to hydrogen. Fermenting biomass into hydrogen has become the research focus on the current international problems. Therefore, the development and use of biological technology to decompose and transform cellulosic biomass resources, which is not only an effective way to use of raw materials, but has great practical significance to solve the world's energy crisis, food shortage and environmental pollution.In this thesis, we study on cellulose biomass bioconversion to hydrogen,and the results were as follows:The cellulase production by Penicillium decumbens L-06 in solid state fermentation (SSF) was investigated using bagasse and wheat bran as the substrate. The optimum conditions for cellulase production achieved by single factor experiments and response surface methodology were: the ratio of bagasse to wheat bran 1:1 (w/w), the ratio of water to material 2.38:1 (v/w), culture temperature 30°C, initial pH 5.28, ammonium sulphate as nitrogen source with the concentration of 1%, 150.5 hours` fermentation period. The maximal cellulase (Filter paper activity) production (3.89 FPU g-1) was obtained under the optimized conditions. The morphology of Penicillium decumbens L-06 in different culture state was observed by scanning electron microscope.Compared dilute sulfuric acid, sodium hydroxide, microwave pretreatment and untreated bagasse on the effect of cellulase hydrolysis (saccharification). Plackett - Burman experimental design, the path of steepest ascent and Box-Benhnken experimental design were adopted to study the pretreatment of bagasse. The effect of these various pretreatment methods by cellulase saccharification was: sodium hydroxide pretreatment > microwave pretreatment > dilute sulfuric acid pretreatment > untreated. When the dosage of cellulase was 250 IU g-1, and the time of saccharification was 36 hours, sodium hydroxide pretreatment, dilute sulfuric acid pretreatment, microwave pretreatment and untreated bagasse after saccharification, reducing sugar was obtained and the concentration was: 200 mg/1 g bagasse, 96.2 mg/1 g bagasse, 98.6 mg/1 g bagasse, 79.3 mg/1 g bagasse, respectivety. The morphology and structure of bagasse before and after treatment was examined by scanning electron microscope.A strain CN1 was isolated from environmental samples which producing hydrogen was efficient from xylose. By Gram reaction, drawing test, oxidase test, scanning electron microscopy, physiological and biochemical identification, 16S rRNA molecular identification and phylogeny. The strain belonged to Enterobacter species and was named as Enterobacter sp.CN1. Then optimizing hydrogen production conditions by Plackett - Burman experimental design and Box - Behnken experimental design, the best combination parameters were: initial pH7.0, cultivated temperature 40℃, xylose 16.15 g / L (0.11mol / L ), yeast extract 2 g / L, peptone 2.54 g / L, FeSO4 250.17 mg / L and MgSO4 800mg / L. Various carbon sources (glucose, xylose, sucrose) as substrate were adopted to produce hydrogen. The final maximum cumulative hydrogen volume was: 1217 ml H2/L xylose medium, 1102 ml H2/L glucose medium and 977 ml H2/L sucrose medium. The maximum hydrogen yield from xylose were 2.0±0.05 mol H2/mol, much more than 0.64 mol H2/mol glucose. Therefore, it can be concluded that fermentative hydrogen production from xylose by Enterobacter sp. CN1 was superior to glucose and sucrose.The strains Enterobacter sakazakii HP and Enterobacter sp. CN1 were co-cultured to ferment the liquid of celluase hydrolysis bagasse after alkali pretreatmented to hydrogen. When the ratio of inoculation between Enterobacter sakazakii HP and Enterobacter sp. CN1 was 3: 1, the maximum cumulative hydrogen volume was 866.53 ml H2/L medium and the maximum hydrogen yield was 1.38 mol H2/mol glucose. Comparing with single strain fermentation, the maximum cumulative hydrogen volume was 812.88 ml H2/L medium and the maximum hydrogen yield was 1.31 mol H2/mol glucose by Enterobacter sakazakii HP; and the maximum cumulative hydrogen volume was 782.87 ml H2/L medium and the maximum hydrogen yield was 1.19 mol H2/mol glucose by Enterobacter sp. CN1. This showed that hydrogen production by co-culture was better and than the single strain fermentation.