【作者】 屈晓凡；

【导师】 廖强； 王永忠；

【作者基本信息】 重庆大学 ， 工程热物理， 2011， 博士

【摘要】 石油、煤炭等化石能源的逐渐衰竭以及日益严重的环境污染使得人们认识到发展替代性的清洁能源的重要性,氢气作为一种清洁能源被认为是人类未来能源结构的重要组成部分。但目前电解水制氢、甲烷水蒸气重整制氢等传统制氢方法能耗高,设备复杂。而利用生物方法制氢可以有效克服传统制氢的诸多缺点,已经引起了人们的广泛关注,其中利用光合细菌吸收光能降解有机废水制氢的方法是目前的一个前沿研究方向。目前光合细菌产氢过程中光能利用率低和产氢速率低的问题较为突出,为了提高光合细菌的光能利用率和产氢速率,增加菌体的抗冲击性,就必须将固定化技术与光合细菌产氢结合起来,包埋法是目前常用的固定化方法之一。包埋颗粒内部为不规则多孔状的复杂微结构,光合细菌被限制于微小孔道内,底物葡萄糖通过扩散作用进入包埋颗粒内部,在微孔道内被光合细菌降解,产生的氢气、二氧化碳等代谢产物分子通过反向作用传递出包埋颗粒。微小孔道为气-液相界面的稳定存在提供了有利条件,因此在固定化包埋颗粒内部会形成气-液-固三相共存的复杂状态,而相界面对光合细菌的生长代谢以及运动都会产生较大的影响。本课题以固定化包埋光合细菌Rhodoseudomonas palustris CQK-01产氢为背景,研究固定化包埋颗粒内部的产氢过程与物质传输现象。首先采用聚二甲基硅氧烷（PDMS）材料制作了可视化微槽道光生物制氢反应器,模拟光合细菌在固定化颗粒内部复杂结构中的代谢产氢过程。实验中发现光合细菌在不同结构形式、不同流动方式的微槽道反应器内的生长过程以及产氢行为存在差异。流速过低过高都不利于光合细菌在微槽道内的生长吸附,半封闭式微槽道反应器内光合细菌生长情况较好,而且可以保持生物量的稳定。贯通式微槽道反应器内气泡主要在槽道内部产生,逐渐生长直至从槽道口脱离。半封闭式微槽道反应器内气泡主要在微槽道的端口处形成并生长。同时,研究了进口底物浓度、进口底物流速、光照强度、光波长等操作条件对微槽道光生物反应器的产氢及底物降解特性的影响规律,最佳的产氢速率、产氢得率、底物消耗速率、光能转化效率分别为1.49 mmol/g cell dry weight/h,0.91 mol H₂/mol glucose,1.63 mmol/gcell dry weight/h和24.36%。在实验研究的基础上,建立了微槽道光生物反应器底物传输及消耗理论模型。分析了光照强度、底物流速、温度、pH值等外界操作条件对光生物反应器内物质传递和底物降解的影响规律,模型预测值与实验值基本吻合。并通过该模型计算了反应器主流道和微槽道两部分区域内的底物浓度分布情况,这对于以后研究固定化包埋颗粒内质量传递具有理论指导意义。固定化包埋颗粒的微小孔道内是多相共存的状态,其中气-液相界面是主要影响光合细菌生长分布的相界面。为了研究微小有限空间内气-液相界面与光合细菌之间的相互作用,设计加工完成平行平板微槽道光生物反应器。通过可视化显微系统拍摄气泡在微槽道内的分布、生长规律以及光合细菌和气-液相界面之间的作用。实验发现光生化反应中产生的气泡多分布于微槽道的边缘部位,同时气泡受到液相中气体分子浓度波动的影响,呈现生长和消失两种相反的现象。光合细菌与气-液相界面的作用是受静电力,范德华力,毛细力,细菌自身动能等因素综合影响的结果,导致光合细菌在气-液相界面具有吸附与排斥两种不同的现象。同时吸附于气泡表面的光合细菌会阻碍相邻气泡间的聚合。气-液相界面的存在有助于液相中溶解的产物气体分子快速析出,因此我们以气-液相平衡和传质理论为基础,将鼓泡法与光合细菌产氢过程相结合,研究了向反应液内鼓入惰性气体强化光合细菌产氢性能的机理。在序批式产氢实验和连续流产氢实验中,通过溶解氢微电极实时监测溶解氢气浓度变化,发现向反应器中鼓入氩气气泡可以有效降低反应液中的溶解产物气体分子浓度,从而降低反应器液相中的气体分压,减小光合细菌产氢过程中的产物反馈抑制作用,使得光合细菌的产氢性能提高。鼓泡过程影响了光合细菌的生长代谢规律,造成光合细菌的生长周期发生改变,同时也改变了中间产物的相对比例和反应液的pH值,在以上多种因素综合作用下光合细菌产氢性能得到了提升。连续流鼓泡光生物反应器在气体流速为10 ml/min产氢性能最佳,此时的产氢速率、产氢得率、光能转化效率分别为5.87 mmol/L/h、3.38 mol H2/mol glucose、47.5%。更多还原

【Abstract】 The fast depletion of the limited fossil fuel (oil and coal) resources and the serious environment issue resulting from the use of fossil fuel have driven us to search for clean energy. Hydrogen has been regarded as the most promising candidate to ensure the future sustainable development, so-called hydrogen economy, owing to its cleanness, high energy density and wide applications. It should be recognized that the realization of hydrogen economy critically depends on the hydrogen production. However, traditional hydrogen production methods, such as water electrolysis and steam reforming of methane have the drawbacks of high energy consumption and complex system. Fortunately, biohydrogen production technologies can overcome these problems and have received ever-increasing attention. Among different biohydrogen production technologies, the use of photosynthetic bacteria to produce hydrogen (photobiohy drogen production) from the organic- contained wastewater is currently a pioneer because of high purity of the generated hydrogen, substrate conversion efficiency and no inhibition of oxygen activity.Although promising, current photobiohydrogen production still encounters the problems of low light utilization and hydrogen production rate. To resolve these problems and improve the anti-impact capability of bacteria, it is necessary to integrate biohydrogen production with immobilization technology. The entrapment technology is such an approach. Typically, the entrapment granules are a complex irregular porous structure, where the photosynthetic bacteria are restricted in micropores. Substrate is transported into the granules by diffusion and then biodegraded by photosynthetic bacteria to produce hydrogen, carbon dioxide and other metabolites who are transported out of the granules. As micropores can stabilize the gas-liquid interfaces, the complicated co-existence of gas, liquid and solid phases is formed in the entrapment granules, which significantly affects the metabolism and movement of photosynthetic bacteria and thereby the biohydrogen production performance. For this reason, this thesis is directed at the biohydrogen production by Rhodoseudomonas palustris CQK-01 to study the coupled hydrogen production and mass transport characteristics in the entrapment granules. Main conclusions are summarized as follows.First of all, a microchannel photobioreactor made by transparent Polydimethy lsiloxane (PDMS) was designed and fabricated to simulate the hydrogen production process by photosynthetic bacteria occurring in the entrapment granule. Experimental results reveal that the microchannel structures and flow behaviors can affect the bacteria growth and hydrogen production performance. Too high and too low flow rate could show negative effects on the photosynthetic bacteria adsorption and growth. Semi-closed microchannel photobioreactor is the best design for the bacteria growth, which also benefits for maintaining the stable the biomass. With respect to the bubble behavior in photobioreactors, it was found that bubbles were mainly formed at the inner microchannel in the flow-through type bioreactor and grew until the detachment from the outlet, while bubbles were mainly formed and grew at the vent region of microchannels in the semi-closed bioreactor. Besides, the effects of the inlet substrate concentration, flow rate, light intensity and wavelength on the biohydrogen production rate and substrate conversion efficiency of the microchannel photobioreactors were examined. The maximal hydrogen production rate, hydrogen yield, substrate consumption rate and light utilization efficiency are 1.49 mmol/g cell dry weight/h,0.91 mol H2/mol glucose,1.63 mmol/gcell dry weight/ and 24.36%, respectively.Based on the experimental results, a theoretical model describing the substrate transport and consumption in the microchannel photobioreactor was developed. With this model, the effects of the light intensity, substrate flow rate, operating temperature and pH value on the mass transport and substrate biodegradation in the photobioreactor were studied. The numerical results are in good agreement with the experimental results. The developed model also predicted the substrate concentration distributions in both the bulk flow channel and microchannel, which is beneficial for the future investigation of the mass transport characteristics in the entrapment particles.As mentioned above, there co-exist multi phases in the entrapment granules and the gas-liquid interfaces play an important role in the photosynthetic bacteria growth and distribution. Hence, to study the interaction between the gas-liquid interfaces and photosynthetic bacteria, a flat-panel microchannel photobioreactor was designed and fabricated. Through the micro-display system, the bubbles distribution, growth as well as the interaction between the photosynthetic bacteria and gas-liquid interface were visually studied. It was shown that bubbles generated by the photobioreaction were mainly positioned at the edge of the microchannel. Due to the fluctuations of the gaseous molecule concentration in liquid phase, bubbles exhibited two contradictory behaviors of growth and disappear. It was also found that the interactions between the photosynthetic bacteria and gas-liquid interfaces depended on the combined effect of the electrostatic force, Van der Waals force, capillary force and bacteria movement, resulting in the adsorption and repulsion of bacteria at the gas-liquid interfaces and in the meantime the photosynthetic bacteria adsorbed on the bubble surfaces can inhibit the bubble coalesce.In addition, because the gas-liquid interface is helpful for the evolution of products from the liquid phase, based on the gas-liquid equilibrium and mass transfer theory, the enhancement mechanism of the biohydrogen production by the inert gas sparging was explored by combining the gas sparging with the photobiohydrogen production. The dissolved hydrogen concentrations were in-situ measured by the dissoluble hydrogen microelectrode in both the batch and continuous operation photobioreactors. It was found that sparging the Ar gas into the photobioreactors could decrease the dissolved hydrogen concentration and thus the hydrogen partial pressure in the liquid phase so that the inhibition of products can be weakened, improving the hydrogen production performance. Meanwhile, the inert gas sparging can also affect the metabolism of photosynthetic bacteria, resulting in the variations of the bacteria metabolic pathway and ratio of different intermediate species and pH value. Because of these effects, the hydrogen production performance by the photosynthetic bacteria was improved. It was found that the continuous sparging photobioreactor yielded the best performance at the gas flow rate of 10 ml/min, corresponding to the hydrogen production rate, hydrogen yield and light utilization efficiency of 5.87 mmol/L/h, 3.38 mol H2/mol glucose, 47.5%, respectively.更多还原