Parameter Optimization And Mechanism Research Of Bio-hydrogen Production From Biomass By Mixed Culture

It is well known that most contries will be on the verge of fossil fuels crisis in a few decades time. And the carbon emissions from the use of fossil fuels have led to global climate changes, environmental degradation as well as health problems. It is urgent to develop non-polluting and renewable energy source. Bio-hydrogen production from renewable organic wastes by anaerobic fermentation represents an important area because it accomplishes the dual goals of waste reduction and energy production. Furthermore, dark biohydrogen fermentation requires less inputs of electricity or energy compared to other hydrogen producing processes such as photosynthetic fermentation. Cellulose as the primary product of photosynthesis in terrestrial environments could be a vast renewable resource for bio-hydrogen production. However, from current situation, the reduction in cellulase production cost and the enhancement of the hydrogen producing bacteria activity are two burning keys to the industrialization of bio-hydrogen production from cellulosic biomass. In ordr to efficiently produce bio-hydrogen from cellulosic biomass, strategies were adopted to optimize the parameters in the bio-hydrogen producton process, and related mechanisms were also studied by physical or chemical methods in this paper. The main contents and results are following:1. The optimization and investigation of the basic parameters in bio-hydrogen production from biomass by anaerobic fermentation. The focus of this study was evaluating the performance and optimal operating conditions of bio-hydrogen from biomass in mixed culture.The seed of hydrogen producing bacteria was harvested from dairy manure compost. Results showed the bio-pretreatment of hydrogen producing substrate using one solid microbe additives greatly enhanced the bio-hydrogen production, and the optimal initial pH value changed along with the different saccharification hydrolysis efficiency of the substrate. The higher the saccharification efficiency was, the lower the optimal initial pH value. When the reducing sugar content in the pretreated substrate was 51.2±3.6%, starch content was 32.4±2.8% and saccharification efficiency was 61.1±3.9%, the cumulative hydrogen yield of 270.5 mL/g TVS was obtained at initial pH value of 7.0. And then statistically analysis based central composite experimental designs were applied to optimize the key process parameters of substrate concentration and initial pH valus for bio-hydrogen production from pretreated cron by dairy manure compost. Experimental results showed both of the two keys had individual and interactive significant influences on bio-hydrogen production yield, but just the substrate concentration had the significant influence on bio-hydrogen production rate. According to the regression analysis, the maximum bio-hydrogen production potential 340mL/g TVSand bio-hydrogen production rate 11.5mL/h TVS were obtained when substrate concentration was lOg/L and initial pH value was 6.0. The detection of main parameters showed in the optimal bio-hydrogen producing period the operational pH range was 5.12-4.79, the oxidation-reduciton potential maintained from-521mV to-458mV, and the main by-product in VFAs was butyrate, which occupied 49.4%-55.7% of liquid by-products.2. Effect of ultrasonic treatment of digestion sludge on bio-hydrogen production by anaerobic fermentation. The utilization of ultrasonic treatment on digestion sludge to enhance microbial activity for bio-hydrogen production was investigated. The objectives of this research were finding out the function of ultrasonic treatment on digestion sludge and making out ultrasonic mechanism on digestion sludge in bio-hydrogen producing process.Experimental results showed the effect of ultrasonic treatment of digestion sludge on bio-hydrogen production was related with the character of the hydrogen producing substrate, when the substrate was more difficult to be utilized, the enhancement effect of ultrasonic treatment of digestion sludge on bio-hydrogen production was more significant. Because the main aim in this study was to evaluate the effect of ultrasonic treatment of digestion sludge on bio-hydrogen production, the actions of hydrogen producing substrate should be avoided, so sucrose was chose as the hydrogen producing substrate, which was easier to be exploited by hydrogen producing bactiria. A Box-Wilson Central Composite Design (CCD) as an effective tool in batch tests was used to optimize the two independent variables of ultrasonic time and ultrasonic power. Regression analysis showed the liner term of ultrasonic exposure time (X1) and its square term as well as the interactive term of the two variables X1 X2 had a significant effect on the ratio of r values with the low P values of less than 0.1, and the liner term of ultrasonic exposure time had the strongest effect on the ratio. The optimal conditions of ultrasonic power and exposure time were 130w/L and 10s, respectively, while the predicted value of the ratio of hydrogen production rate obtained was 1.34. Total volatile fatty acids (VFAs) and three main by-products as well as carbohydrates changes in bio-hydrogen production processes between the ultrasonic treatment digestion sludge and the one without ultrasonic treatment were measured. Results implied the utilization of ultrasound to treat digestion sludge did not denature the biodegradation paths for bio-hydrogen production. Hydrogen production rate ratio of 1.48 appeared when ultrasonic treatment was applied directly on both substrates and digestion sludge at the same time, and the ratio of 1.17 was observed when ultrasound was just executed on substrates. Results also showed ultrasonic treatment of digestion sludge could greatly increased the soluble CODs concentration of digestion sludge. So the mechanism of ultrasonic treatment of digestion sludge on bio-hydrogen production was assisted in decentralizing the biological floc and disrupting large organic particles into smaller-size particles but not killing the microorganisms. Meanwhile, ultrasound disassembled the flaccid surface of digestion sludge and released the intercellular materials to the aqueous phase.3. A two-phase process combined cellulase production and bio-hydrogen production from cornstalk was constructed. Strategies were adopted to cost-efficiently produce cellulose-hydrogen by anaerobic fermentation in this study. First, cellulase used for hydrolyzing cellulose was prepared by solid-state fermentation (SSF) on cheap biomass from Trichoderma viride. Second, the crude cellulase was applied to cellulose-hydrogen process directly.When cellulase was produced, several cultural conditions for cellulase production on cheap biomass such as moisture content, inoculum size and culture time in solid-state fermentation were studied. According to the experimental results, the maximum cellulase activity was obtained at moisture content of 55%, fermentation substrates of lOg in 250mL flask, inoculums size of 15% and culture time of 4 days. And then the components of solid-state medium were optimized using statistical methods to further improve cellulase capability. Plackett-Burman experimental design was adopted to find out the important components in medium, which were MgSO4, corn bran and KH2PO4. Path of the steepest ascent was employed to find proper direction of the three changing variables. The significant independent variables of MgSO4, corn bran and KH2PO4 were further explored using Box-Behnken design. Regression results showed the maximum predicted value of FPA obtained was 8.9 IU/gds, when the optimal variables values were MgSO4 of 0.20 %, corn bran of 9.0% and KH2PO4 of 0.61%, respectively. The FPA values of cellulase increased 37% compared to the one before the optimization of medium compoents. When the cellulase was applied in cellulose-hydrogen production from cornstalk wastes, the effects of the dosage of the crude cellulose on the components of the corn stalk wastes and saccharification efficiency were tried at 40℃in anaerobic condition for 3 days. Cellulose, hemicellulose, and lignin as main components were analyzed before and after hydrolytic pretreatment of cornstalk wastes. Results implied that the enhanced soluble saccharides mostly came from the biodegration of hemi-cellulose and the crude cellulase had significant effect on hemi-cellulose than on cellulose and lignin. The dosage of 1IU/g cornstalk wastes was obtained as the proper proportion for cornstalk wastes hydrolysis by this crude cellulase. Bio-hydrogen production was carried out using hydrolytic cornstalk wastes as substrates and dairy manure compost as seed by anaerobic fermentation. The maximum cumulative hydrogen yield 122mL H2/g-TVS was obtained at initial pH 6.5, dairy manure compost concentration of 100g/l, substrate concentration of 20g/l and culture time 53h. This valure was about 45-fold than that from raw cornstalk wastes.