Characteristics Of Mass Transfer And Hydrogen Production Of Photo-bioreactor With Immobilized Photosynthetic Bacteria

Currently, energy resource remains in strain, and the international price of oil keep on rising, so the primary problem affecting the development of society and economy is shortage of energy resource. Meanwhile, the exploitation and application of fossil fuel bring serious harm to our environment, especially CO2 emitted breeds in the greenhouse effect to induce the extreme change of climate, and the acid rain is ascribed to the emitted NOx and SO2. These pollutants threaten the sustainable development of earth and human being. Nevertheless, in our country falling short of energy resource the amount per capita of oil and natural gas is only 7.7% and 7.1% of word average level. Therefore, the exploitation of renewable bioenergy will hasten the development of sustainable development of society, in which hydrogen named as a promising energy source is a clean and efficient fuel and widely accepted as a potential substitute for fossil fuels by virtue of the fact that it is renewable and does not cause the''greenhouse effect". And in the 11th Five-Year Plan of energy resource promulgated the exploitation of hydrogen energy will become one of the important and advanced technologies developing. However, hydrogen production by conventional methods needs to consume the fossil energy resource and destroys our living environment, conversely hydrogen production by photosynthetic bacteria (PSB) from organic wastes is renewable. So far, the immobilized cells technology has became hot in biotechnology, but there was little research on the transfer characteristics of immobilized PSB cells in the process of hydrogen production, but the research, which will lay a foundation for application of immobilized cells technology in bioenergy, will favor to solve the problem of limitation in mass transfer of immobilized cell and the problem of low efficiency of light utilization and low rate of hydrogen production.The characteristics of hydrogen production and substrate transfer of immobilized PSB was mainly analyzed in the thesis. First, a strain identified as Rhodoseudomonas palustris with high efficiency of hydrogen production was isolated and purified from sewage sludge. Effect of light wavelength, light intensity, substrate concentration, pH value of culture medium and culture temperature on the kinetics of hydrogen production in batch culture was studied in experiments, And according to experimental data the empiristic formulae on effect of different culture conditions on the maximum specific growth rate were gained. Moreover, kinetic models on biomass growth, substrate consumption and hydrogen production of PSB were respectively established, which reflected the effects of operation parameters in batch culture on the kinetics of growth, substrate concentration and hydrogen production, respectively.The research on characteristics of hydrogen production and substrate consumption in the particle of immobilized PSB was tested, and the mathmatic model on the substrate transfer and consumption in entrapped-particles was studied, which results reflected on effect of parameters in continuous culture on the characteristics of substrate transfe. The research results releaved that substrate was transported into particle by diffusion, and the concentration of substrate in particle decreased with decrease of radius of particle. According to above analyzed the conclusion that the limited process in particles was biochemical reaction was deduced. Therefore, the key of improving biochemical reaction efficiency of the entrapped-particles was to improve the biochemical characteristics of strain of PSB.On the other hand, the results on photo-bio-hydrogen production in packed beds filled with particles of immobilized cells revealed that consumption of substrate in the packed beds would divert to the process limited by biochemical reaction from that controlled by mass transfer of substrate with increasing concentration of substrate or with increasing flux. And light energy became compressed condition from limited condition with light intensity increasing. However, effect of light wavelength on biohydrogen production by PSB was complicated with dealing with light intensity, which indicated that different excited phase of the photosynthetic antennae system was inspired by different light wavelength and that the photo-chemical efficiency changed correspondingly. In addition, the rates of hydrogen production and substrate consumption in packed beds filled with porous medium increased with pH value of culture medium or culture temperature increasing, and then declined with these parameters increasing continuously.Moreover, the research on characteristics of packed-bed with biofilm showed that in certain other parameters, low intensity was limited condition, vice versa, it was impressed condition, and that in limited substrate concentration condition, the metabolism in the pached bed was controlled by mass transfer, conversely by biochemical reaction. Meanwhile, the results revealed that in low flux condition, the metabolic process controlled by mass transfer was obtained, conversely the process controlled by biochemical reaction was gained in high flux and high substrate concentration at inlet. According to experimental results, the model on mass transfer and substrate consumption was founded, in which the operation conditions effecting on mass transfer in biofilm packed-bed were analyzed respectively. And the results predicted by model were accordant with experimental data.Furthermore, the results in the thesis indicated that in all conditions the optimal temperature and the optimal pH value of hydrogen production by PSB was 30°C and 7.0, respectively, which revealed that the culture temperature and pH value affected the activities of enzyme in cells mainly.