The Experiment And Simulation Of Photosynthetic Bacterial Biofilm Growth Characteristics

With the economic development and the increasing requirement of energy for human being, the exploitation and utilization of clean energy is becoming a general trend. It is of great developing potential to exploit hydrogen energy as a clean recyclable energy. Organic discard can be descended into hydrogen by photosynthetic bacteria at the driving of sunlight power, then, the recycling use of the administration of pollution can be realized. Bioreactor of photosynthetic bacterial biofilm can process organic discard effectively and can produce clean hydrogen in a large quantity at the same time. This is an advanced technology of great potential in the comprehensive utilization of organic discard and environment protection.For the photosynthetic bacteria growing process in the plate-type bioreactor for biofilm development, a series of experiments on the effects of wavelength, wave-strength, flow flux and nutrition of the circulating liquid on the growth characteristics of the high-efficiency hydrogen-production photosynthetic bacterial biofilm were carried out with the help of the on-line observation of the micro-organization of photosynthetic bacterial biofilm and off-line analyse of the growth characteristic of bacterial biofilm in the present study. Then, the effects of these important parameters that affecting the surface coverage rate, thickness, dry weight, and density of rhodoseudomonas palustris biofilm were discussed, respectively. On the basis of experimental studies, the cellular automation model was adopted to simulate the structures of biofilm. The launching of this study, the absorption and growth mechanism on solid substratum of photosynthetic bacteria was revealed;at the same time, the experimental basis for the starting up of bioreactor for photosynthetic bacterial biofilm was offered; and the basic material for the development of processing polluted water and the making of hydrogen technology was offered as well. The main research results are as follows:1) Under the conditions of light wavelengths varying from 420 nm to 590 nm, the surface coverage rate of the biofilm increases with an increase in light wavelength while the dry weight of biofilm keeps almost constant at the same time period. The thickness of biofilm decreases with the increase in light wavelength after 4 days. A longer light wavelength leads to a solider biofilm with a larger density.2) Under the conditions of light wave-strength varying from 1000lx to 8000lx, the surface coverage rate of the biofilm is the highest at the light wave-strength of 5000lx at the same time period. Under the conditions of light wave-strength smaller than 5000lx, the dry weight and density of biofilm increases with an increase in light wave-strength while the thickness of biofilm decreases after 4 days. The dry weight and thickness of biofilm is lowest at 8000lx, and the differences of biofilm density are unobvious at light wave-strength of 8000lx and 1000lx.3) Under the conditions of flow flux varying from 37.8 ml·h-1 to 1080 ml·h-1, the surface coverage rate of the biofilm increases first and then decreases with an increase in flow flux at the same time period. When the flow flux is higher than 228 ml·h-1, the growth characteristic parameters of biofilm are less effected by the different flow flux. The thickness of biofilm is largest while the density is lowest at the flow flux of 37.8 ml·h-1.4) Under the conditions of substrate concentration varying from 0.05 g·L-1 to 10 g·L-1, the surface coverage rate of the biofilm is highest at substrate concentration of 10 g·L-1 at the same time period. The dry weight and thickness of biofilm are less effected by the different substrate concentration, while the density of biofilm increases with an increase in substrate concentration.5) Among all the affecting parameters, the effect of sunlight to the morphology of photosynthetic bacteria and the structure of photosynthetic bacterial biofilm is the most significant. The cell division and production of extracellular polymeric substance (EPS) were restrained, which then, affects the morphology of the individual bacteria and structure of respective biofilm, when the wavelength of light is 420nm;the biofilm changes into the shape of long irregular strips and the coverage rate of biofilm is the lowest when the wave-length of light is 8000lx; the effect of the flow of circular fluid on the film-forming rate of photosynthetic bacteria on the surface of solid and fluid is most significant; the biofilm grows at the slowest speed, but the rate of growing does not increase with the increase of flowing speed when the flow is 37.8ml/h. Nutrition limitation can promote the growth of the floating photosynthetic bacteria in a fixed way and can make the biofilm structure porous, which is the living strategy to the unfavorable environment of photosynthetic bacteria.6) Combined with the growth of photosynthetic bacteria and the differential equation of nutrition spreading of the inner-biofilm, the cellular automation model for the growth of photosynthetic bacteria was established, and the growth process of biofilms of photosynthetic bacteria under different experimental conditions was simulated mathematically. The results show that the photosynthetic bacterial biofilm is irregular structure with many bores. A higher liquid shear leads to a flatter surface of biofilm. The biomass increases first and then decreases with an increase in light wave-strength, the differences of biofilm structure are little at light wave-strength of 8000lx and 1000lx. The density of the biofilm is the lowest at light wavelength of 420nm and lower substrate concentration. The biomass and thickness increase with an increase in light wavelength and substrate concentration.