| In the last few decades, the price of fossil fuels kept on rising, and the shortage of energy resource has hindered severely the social and economic development. Meanwhile, the excessive exploitation of fossil fuels is destructive to the environment. However, hydrogen has the highest caloric value, and the combustion product is water without producing emissions that contribute to environmental pollution. Therefore, hydrogen is considered as the most clean energy alternative to fossil fuels. In the kinds of hydrogen production means, the photo-biological fermentation process by photosynthetic bacteria (PSB) has been used to produce hydrogen because of wider light absorption spectrum, high theoretical energy conversion efficiency, moderate reaction condition and most environmentally friendly route. This is favorable for realizing the sustainable energy development strategy.The research on the mass and energy transport in the hydrogen production process of PSB is very significant in the aspects of solving the low substrate transmembrane transportation rate, hydrogen production rate and light conversion efficiency. Up to now, the hydrogen production principle of PSB has been focused in the biological energy field, and few studies have addressed the hydrogen production principle, specially the mass and energy transport processes in hydrogen production by PSB. Meanwhile, the process of photon harvesting and electron transfer was studied on the condition of cell destruction, and light transport was no relation with intracellular substance metabolism..In the article, an indigenous photosynthetic bacterium designated Rhodoseudomonas palustris CQK-01 for phototrophic hydrogen production was isolated from local municipal sewage sludge. The experiments were set up for studying the biological characteristics and the growth and hydrogen production kinetics in batch culture on the condition of initial substrate concentration, initial pH value, illumination wavelength and illumination intensity. In the perspectives of light transport and substrate transmembrane transport, the light attenuation characteristics, the photosynthetic pigments, the intracellular ATP concentration, the permeability of photosynthetic membrane and the intracellular substrate concentration was investigated experimentally under the operation parameters included initial substrate concentration, initial pH value, illumination wavelength and illumination intensity, and the effect of light and substance metabolism on hydrogen production rate was investigated. Meanwhile, the experimental association formula of light attenuation and the model of glucose transmembrane transport and metabolism were conducted. For enhancing the hydrogen production performance of PSB, the effect of ultrasonic output power, ultrasonic time, substrate concentration, etc. on hydrogen production was studied in the batch and continuous ultrasonic photo-biological reactor. The main results were summarized as follows:?The growth and propagation ways, bacterial morphology, absorption spectrum of R. palustris CQK-01 was experimentally obtained, and the study revealed the change law of the specific growth rate, substrate removal rate and hydrogen production rate under various initial substrate concentration, initial pH value, illumination wavelength and intensity.?The effect of optical length, bacterial concentration, incident illumination wavelength and illumination intensity on light attenuation was studied in the batch photo-biological reactor. The results showed that in the range of visible light, the coefficient of light attenuation increased with illumination wavelength decreased, and increased with bacterial concentration increased. Furthermore, the results which were calculated by the experimental association formula of light attenuation with illumination wavelength and bacterial concentration are in agreement with those measured by experiment methods. The light attenuation resulted in the very unevenly distribution of illumination intensity along the optical length in the batch reactor. The growth rate of PSB was the fasted and the hydrogen production rate achieved early the maximum value in the shorter optical length and higher illumination intensity. When the optical length is 0.05 m, and the photo-biological reactor has the optimal hydrogen production performance, where the hydrogen production rate was 0.16 mmol/L/h, glucose removal rate was 0.49 mmol/L/h, hydrogen yield was 0.4 mol-H2/mol-glucose and the energy conversion efficiency was 28%.?On the conditions of various initial substrate concentration, initial pH value, illumination wavelength and illumination intensity, the photosynthetic pigments and intracellular ATP concentration was experimentally studied in the process of hydrogen production by PSB. The experimental results indicated that the carotenoid and bacteriachlorophyll pigment had different synthesis mechanism, and the carotenoid pigment content was higher than bacteriachlorophyll content. When the illumination wavelength was 590 nm, initial substrate concentration was 75 mmol/L and initial pH value was 7.0, the PSB have a strong ability for adjusting the photosynthetic pigment and photophosphorylation. The maximum carotenoid and bacteriachlorophyll pigment was 2.3, 2.5 mg/g cell dry weight, respectively, and the maximum hydrogen production rate was 2.3 mmol/g cell dry weight/h.?The characteristics of glucose transport across cell membrane in a batch photobioreactor using Rhodoseudomonas palustris CQK-01 were experimentally investigated and the intracellular glucose concentration and glucose permeability coefficient were calculated based on the law of Fick and Michaelis-Menten equation, respectively. The results showed that the maximum glucose cross-transport rate of 9.74 mmol/g cell dry weight/h was obtained, and the maximum permeability coefficient of the cell membrane kept almost same as 250 cm3/g cell dry weight/h. Meanwhile, the model of glucose transmembrane transport hydrogen production was established according to the single cell model, and the intracellular and extracellular glucose concentration and hydrogen concentration of PSB was also analyzed.?The influences of ultrasonic wave on hydrogen production by PSB were investigated. The results revealed that the ultrasonic treatment could change and thin the photosynthetic membrane, resulting in an improvement in the membrane permeability, and finally, promote substrate transmembrane transportation. Meanwhile, ultrasonic wave could produce cavitation and acoustic streaming, and the cavitation would generate powerful shear forces to release the molecule of hydrogen in the liquid which eliminate the inhibition of hydrogen partial pressure on the growth and hydrogen production of PSB. In the batch ultrasonic reactor, the PSB exhibited the best hydrogen production performance which the hydrogen production rate, hydrogen yield and energy conversion efficiency was 0.54 mmol/L/h, 1.18 mol-H2/mol-glucose and 11%, respectively. In the continuous ultrasonic reactor, the hydrogen production rate, hydrogen yield and energy conversion efficiency of the PSB was 0.82 mmol/L/h, 0.33 mol-H2/mol-glucose, and 2.7%, respectively. It was also showed that the hydrogen production rate and energy conversion efficiency with PSB with ultrasonic wave were increased to be nearly 1.5 times higher than that with PSB with non-ultrasonic. |
PDF Full Text Request