The Technology And Relative Mechanism Of Continuous Process For Hydrogen Production By Photosynthetic Bacteria

Energy shortage and environment pollution, resulted from energy production and consumption, have been the most serious problems people have to confront in 21th century. It is essential for people to exploit sustainable energy and build a brand-new energy system with a view to environment protection and national energy safety. Therefore, it is the effective way to develop and utilize renewable energy instead of continuous consumption of fossil energy. Up to now, developing renewable energy has been a common sense around the world.Because of its advantages, such as clean, no consumption of fossil resource and so on, biohydrogen production is given great countenance by many countries. For one thing, photosynthetic bacteria have the function of combining solar energy utilization and organic compound conversion with hydrogen production; which set up the foundation for achieving the goal of converting solar energy and organic compound into hydrogen, hence, photosynthetic bacteria have been frequently claimed as promising candidates for the development of hydrogen production system. For another, the mechanism and metabolic pathway of hydrogen production by photosynthetic bacteria are very complex and needed to be further studied in the future. The present macro-data about hydrogen production by photosynthetic bacteria has its practical significance for the industrialization of hydrogen production by photosynthetic bacteriaOn one hand, in this study, synthetic characteristics of mixed photosynthetic bacteria are investigated, and on other hand, a system and process of continuous biohydrogen production are developed. The main interest in this study is to propose a new process for hydrogen production by photosynthetic bacteria and provides some thoughts and datum for further development. The main research results of the dissertation are as following:1. Mixed photosynthetic bacteria (MPSB) are facultative anaerobic bacterial flora. They grow well without intentional anaerobic culture; but, a strict anaerobic environment is needed in which air in the headspace of the bioreactor has been removed by CO₂ before hydrogen production. The change of illuminance intensity has little impact on MPSB growth and hydrogen production. The optimal light condition for MPSB is about 1000Lux; higher light intensity would formed a barrier of light, which deters light from penetrating and then MPSB could not obtained adequate light. MPSB could tolerate bad treatments such as temperature, light, microbial contamination and so on. Above all, they are suitable for industrial application with good environmental adaptability.2. The experiment comes to the conclusion that growth curve of MPSB under fixed incubation condition is very special, for the trend line of growth curve is close to linear. The more inoculums'size of MPSB, the more proliferation rate. Hydrogen production by MPSB is non-growth-linked product and MPSB die gradually when hydrogen production begins. A special photo bioreactor should be employed to cultivate production strains of MPSB for hydrogen production process. There exists an acid production process in the hydrogen production process by MPSB, whose substrate is glucose. Acid production process leads to pH decrease from 7.0 to 5.0 below. The optimal condition for hydrogen production is as following: 30℃, 1200Lux, inoculums'size 10%²0% (v/v), with 3% of glucose concentration.3. A set of special equipment named as plug flow continuous culture system with culture solution recycles is made successfully, by which the production strains of MPSB are aeecssible to be cultivated continuously and the fluctuation range of cell concentration at the outlet was less than 4%. The bioreactor with internal (optical fiber) light sources is made as cylindrical standing can, in which transparent sleeves are installed to settle optical divider. Conventional plastic-clad end-light optical fibers are polished mechanically to obtain side-light optical fibers allowing light emission from the entire surface of fibers core. In order to drive the liquid in reactor to close to plug flow, inlet is set at the bottom of standing can in tangent direction; outlet is set at the top of standing can by the same way, meanwhile, all the liquids imported are pumped into the can through the inlet by metering pumps. Mathematic model about continuous culture process of MPSB is built in this paper. The optimal way for continuous culture of MPSB is that culture medium flow equals to recycle flow of culture solution and outlet flow of production strains, hydraulic retention time (culture time) in the reactor is the double of cell under the special initial concentration.4. In this paper, a continuous photo-bioreactor is designed for continuous biohydrogen production by MPSB, in which operating methods are dealt with. Initial OD660 of photosynthetic bacteria culture solution is of 0.56, flow rate of growth culture medium, culture solution recycles and outlet are all of 0.21L/h. H₂ production velocity of reaction solution reaches 2.68L/L? h, H₂ production was the 86.5% of the batch H₂ production.5. One of the experiments is focused on the influence of headspace pressure on H₂ production, which is produced by mixed photosynthetic bacteria, whose substrate is glucose. The inoculums'sizes are 10%, 20%, 30%, 40%, 50% respectively, meanwhile, headspace pressure are at levels of 0.001MPa,0.000MPa,-0.001MPa,-0.002MPa,-0.003MPa,-0.004MPa,-0.005MPa. It comes to the conclusion that delay time of H₂ production is shortened, at the same time, H₂ production velocity and the output of H₂ production are increased with the reduction of headspace pressure. It is obvious that production time is shortened, efficiency and output of H₂ production are improved by headspace pressure reduction, which makes the H₂, and CO₂ pressure decrease, thus solubility is dropped, therefore, feedback inhibition is removed or weakened.