Studies Of Clostridium Butyricum Medium Optimization And H₂ Production From Sugarcane Bagasse And Jatropha Hulls

Hydrogen as a clean and renewable energy resource has received widespread attentions of researchers. Compared with other developing methods of hydrogen production, biohydrogen (or biological hydrogen) production technology has many advantages such as pollution-free, lower cost and renewable. Among several biohydrogen technology, dark fermentation has many advantages such as no requirement of illumination and oxygen, as well as enlarged biomass source and continuous course for hydrogen production. Therefore, the industrialization of dark fermentation can be enlarged easily, while low hydrogen yield and high substrate cost hampered this development. Considering this point, four related issues were studied in this thesis:(1) The optimization of culture medium for H2 production from glucose under Clostidium butyrium fermentation using response surface methodology.During the fermentation, the optimized fermentation medium for the growth of bacteria cells might be not the best medium for the production of hydrogen. In order to improve both the rate and the yield of hydrogen, several experimental evaluation and mathematical statistical methods including single-factor test, Plackett-Burman design, steepest ascent experiments and central composite design were applied to study the effects of several key variables during the Clostidium butyrium fermentation using glucose. The results demonstrated that the composition of the optimum fermentation medium were (g/L):glucose,15.66; yeast extract,6.04; tryptone,4; K2HPO4,3; KH2PO4,3; L-Cysteine,0.05; MgSO4·7H2O,0.05 and FeSO4·7H2O,0.3, which gave the highest yield of 2.15 mol H2/mol glucose. Both the concentration of glucose and yeast powder had significant effects on the yield of hydrogen.(2) Two-stage dilute acid hydrolysis of sugarcane bagasse and Jatropha hulls for the production of hydrogenSugarcane bagasse and Jatropha hulls, the waste of two typical plants in the tropics and subtropics like Yunnan province, were used as raw materials for the hydrogen production via two-stage acid hydrolysis followed by Clostidium butyrium fermentation. The results demonstrated that the conditions for the first hydrolysis step were 1.5% of H2SO4, solid/liquid ratio (SLR) of 1 g:10 mL, temperature of 130 ℃, time of 60 min, while the conditions for the second step were 3% of H2SO4, SLR of 1 g:10 mL, temperature of 150 ℃, time of 60 min, which finally produced the optimal hydrolysis yield of 69.3%. Using the hydrolysates from bagasse and Jatropha hulls containing initial total reducing sugar (TRS) content of 15.66 g/L as the carbon source, high hydrogen yields of 2.06 and 1.95 mol/mol TRS were achieved for bagasse and Jatropha hulls, respectively. Two-step hydrolysis could avoid hemicellulose loss under servere reaction conditions and incomplete hydrolysis of cellulose under mild conditions, which resulted in the both full utilization of hemicellulose and cellulose in Jatropha hulls and bagasse, and provided high yields of target products.(3) Hydrolysis of Jatropha hulls by combined catalysis of Lewis acid and diluted H2SO4 for biohydrogen production.Jatropha hulls were pretreated by hot water and neutral, acidic, alkaline detergent, which was expected to lower the negative influence of the extractable impurities in the raw materials on the hydrolysis and fermentation of hulls. It seemed that neutral detergent removed most of extractable substances in hulls, but exerted less impact on the loss of lignocellulose part. Neutral detergent also disrupted the amorphous structure in lignocellulose, which resulted in increased content of cellulose and hemicellulose and improved cellulose crystallinity. Several Lewis acids were tested to assist the hydrolysis of Jatropha hulls under the catalysis by diluted H2SO4, which might reduced the reaction severity with only H2SO4, and further improved the effectivity and selectivity of hydrolysis reactions. The results demonstrated that FeCl3 provided the best synergetic performance with H2SO4 during the hydrolysis of hulls. FeCl3 effectively solubilized hemicellulose into monomeric and oligomeric sugars, and exposed cellulose part for benefited hydrolysis. FeCl3 further improved the yield of glucoce through the enhanced hydrolysis of cellulose. The hydrolysis conditions of hulls were also optimized, and the highest TRS yield of 56.9% and TRS concentration of 12.07 ± 0.12 g/L were obtained under the conditions:0.11 mol/L FeCl3,1% sulfuric acid,132.5 ℃,58 min and SLR of 1 g:12 mL. Clostidium butyrium fermentation using this hydrolysate gave high hydrogen yield of 1.78±0.01 mol/mol TRS.(4) Production of activated carbon from the hydrolysis residue of Jatropha hulls and its use in the detoxification of hydrolysate.The hydrolysis residue of Jatropha hulls was carbonized at 500 ℃ for 1 h to prepare biochars, which provided higher biochr yield and superior physical adsorption capacity than the biochar from hulls under the same carbonization conditions. Response surface methodology was introduced to optimize the KOH-activated treatment of biochars, and the optimum activated carbon yield of 63.02%(predicted value) was obatined at 743 ℃ for 107 min, with the weight ratio of KOH to biochar of 3:1.