Photosynthetic Bacteria Growth And Transport Phenomena In Microchannels Photobioreactor For Hydrogen Production

Energy crisis and environmental pollution are two major problems for human beings. Hydrogen is universally considered as one of the most promising energy resources due to its advantages of high caloric value, burning with no pollution and renewable. Biohydrogen production by photosynthetic bacteria (PSB) can simultaneously degrade organic wastes and utilize solar energy. Therefore, this technology is expected to be one of the promising options for H2 production.The immobilization technology used to photo-biohydrogen production can effectively reduce the loss of biomass amount in bioreactors, resulting in increase in the hydrogen production rate and substrate conversion rate. However, light penetration and mass transfer within granule are two outstanding issues for this technology. For the further understanding of the behavior of hydrogen production by PSB and mass transfer within immobilized granule, a visualized microchannels photobioreactor was designed to observe the adsorption and growth of PSB, named as Rhodopseudomonas palustris CQK 01 in the microchannels. Then the hydrogen production performance, substrate degradation, and bubbles growth and motion in the microchannels photobioreactor were investigated.In the present study, the first attempt was devoted to the exploration and improvement of the microchannels'fabrication method and then the PDMS microchannels and other components of the reactor was designed and fabricated . The effect of flow condition on the behavior of PSB growth in microchannels photobioreactor was investigated. Then the effects of influent substrate concentration, flow rate, illumination intensity and illumination wavelength on the characteristics of hydrogen production and substrate consumption of the microchannels photobioreactor as well as bubbles growth and motion were investigated. Based on the experimental results, the model of the mass transfer of substrate in the microchannes photobioreactor with photo-biochemical reaction was established.Obtained the main results were shown as following:1) The condition with illumination wavelength of 590 nm, illumination intensity of 5000 lux, flow rate of 1.5 mL·h-1 and room temperature was the optimal environment for PSB growth in the microchannels. The PSB behavior in the microchannels can be divided into four stages, including diffusion and adsorption, bacteria reproduction, morphological transformation and formation of PSB colony.2) Under the condition of light wavelength of 590 nm, light intensity of 5000 lux, flow rate of 1.5 mL·h-1 and room temperature , the maximum hydrogen production rate and hydrogen yield were 2.4 mmol·g -1 cell dry weight·h -1 and 0.78 mol H2·mol-1 sub, respectively. Both the inhibition of substrate and the loss of biofilm resulted in the lower hydrogen production rate and hydrogen yield at high substrate concentration and flow rate of the influent solution. Light inhibition effect resulted in decrease of hydrogen production rate at high illumination intensity.3) The growth and motion of bubbles in microchannels can be divided into four stages, including nucleation, spherical bubbles growth, the bubbles growth along microchannels extruded by lateral and bubbles separating from microchannels. The erosion of the bubbles and fluid shear force caused by the bubbles'growth and motion resulted in the loss of biomass in microchannels. Gas molecules diffused into the surrounding liquid was the main reason of bubbles'dissolving, when the local hydrogen concentration was below the saturation concentration in microchannels liquid.4) The theoretical model of mass transfer of substrate in microchannels photobioreactor was established. The results showed that the datas calculated from the model had a good agreement with the experimental values.