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题名:
基于微藻闪光效应的光生物反应器设计方法
作者: 薛升长
学位类别: 博士
答辩日期: 2011-11-25
授予单位: 中国科学院研究生院
导师: 丛威
关键词: 微藻 ; 闪光效应 ; 光效率 ; 光纤光生物反应器
其他题名: Design of Photobioreactors Based on “Flashing Light Effect” of Microalgae
学位专业: 生物化工
中文摘要: 传统的仅将反应器几何特征、流动条件、比照光面积等作为关键参数进行光生物反应器设计和放大的方法,未能从单个藻细胞对光照的最佳生理需求的角度设计和放大光生物反应器,使得反应器光区和暗区混合差、细胞产率低。如何以较低的能耗实现高的光效率是未来光生物反应器的发展方向。为了获得微藻细胞生长的生理最佳光照条件,本论文首先构建了一套可用于研究微藻在各种光照条件(持续、周期)下生理特性的闪光效应研究平台。使用大功率白光LED作为光源;以时间继电器和部分透光的圆盘转动两种方式结合实现光/暗循环;薄层反应器内藻细胞光照条件均一性好且精确、可控,能最大程度反映单个藻细胞对各种光照条件的响应。在此平台上研究了钝顶螺旋藻、二型栅藻、球等鞭金藻的闪光效应,结果显示:在各种光强、光比例的周期光照条件下,提高光/暗频率均能提高微藻比生长速率/净光合活力/光效率,提高幅度主要受光强影响,光强越高,提高幅度越大,最高可提高3倍以上;光/暗频率超过10 Hz之后,比生长速率/净光合活力/光效率基本不再变化,趋于稳定。通过综合分析,获得了微藻细胞生长的生理最佳光照条件,即光强和光比例的乘积k*I进入该藻种生长的光限制区,且光/暗频率达到10 Hz以上。这可作为指导光生物反应器设计的一套综合性方法。就上述光照条件在反应器中的实现,本论文尝试使用光纤合理布置于反应器内作为内光源,以充分发挥微藻闪光效应为核心,从理论上对闪光效应光纤光生物反应器进行了设计型和操作型计算;构思了三种可充分发挥微藻闪光效应的光纤光生物反应器结构:气体驱动的箱式结构、泵驱动的板式结构和搅拌罐结构,它们的共同特点是藻液流动方向垂直于光纤或者在光纤垂直方向上有一定的速度分量。在上述构思的基础上,本论文具体设计和构建了一套中等规模(130 L)的气升板箱式光纤光生物反应器。对光强分布、气液传质、光/暗频率等进行的测试显示其具有良好的性能;将其用于螺旋藻、栅藻培养,结果显示,光纤反应器在相同的体积光能输入条件下,生长速率和光效率分别比整体光/暗频率较低的气升式反应器提高38%和28%以上;光纤反应器培养栅藻的光效率(7.1%)分别是室外管式(1.5%)、板式(1.9%)、柱式(5.4%)反应器光效率的3.8倍、2.7倍和1.3倍;表明以充分发挥微藻闪光效应作为指导光生物反应器设计的方法具有可行性和有效性。在此基础上,对规模化光纤光生物反应器系统进行了概念设计,并对其产能进行了估算。
英文摘要: Microalgae use solar energy to transform inexpensive natural resources, e.g. CO2, H2O and inorganic salts, into protein, polysaccharide, lipid, biological pigments, vitamins, polyunsaturated fatty acids (PUFAs) and other valuable products through photosynthesis, and provide possible solutions to the urgent issues faced by human beings today, such as energy, resource and food shortage, global warming and environmental problems. Currently, the bottleneck limiting large-scale utilization of microalgae is their high cultivation cost, which is typically expressed in low light efficiency and high energy consumption for fluid mixing. The main reason is, traditional approach which uses geometrical features, flowing conditions and specific illumination area as the critical parameters for photobioreactor design and scale-up, failed to grasp the key limits of photosynthetic efficiency in microalgae cultivation. In other words, traditional method failed to keep physiologically optimum light conditions for each algal cell while designing and scaling up photobioreactors, giving poor mixing between light regions and dark regions and thus low productivity. Althrough some novel photobioreactors were designed to increase mixing between light regions and dark region through inner structure (e.g. baffles and static mixers, etc) and intensified turbulence in reactor to increase photosynthetic efficiency, this also leaded to significant increase of driving energy consumption and great difficulties of reactor manufacturing and cleaning caused by complicated structure. To attain high photosynthetic efficiency with low energy consumption is the direction of future photobioreactor development. Aiming at these problems, this work mainly focuses on the following problems. Firstly, to clarify the physiologically optimum light conditions for microalgae growth through the research of “flashing light effect” (FLE), and secondly, to realize these light conditions in photobioreactor with low energy cost. Finally, the design method of photobioreactors based on FLE of microalgae were constructed and experimentally verified. In order to obtain physiologically optimum light conditions for microalgae, a “flashing light effect” research platform was constructed to investigate microalgae’s physiological characteristics under continuous and intermittent light conditions. High-power-white LED was adopted as the light source to give high light intensities (0~4000 μmol m-2s-1), comparable to that of direct sunlight; the integration of the two modes to realize light/dark alternation could give rather wide range light/dark frequencies (0.01~100 Hz), which could cover the light conditions algal cells experienced in any reactor configurations. In addition, light conditions algal cells experienced in thin-layer reactor were well uniform and controllable, thus reflecting real responses of algal cells to various light conditions. Afterwards, “flashing light effect” of Spirulina platensis, Scenedesmus dimorphus, Isochrysis galbana were investigated with the platform. The results showed that specific growth rate/net photosynthetic activity/photosynthetic efficiency could be improved by increasing light/dark frequency under intermittent illumination of any light intensity and light fraction, and the increment largely depended on the applied light intensity. The higher the light intensity, the greater is the increment, and the greatest of which was more than 3 times of that under continuous illumination. The results also showed that specific growth rate/net photosynthetic activity/photosynthetic efficiency increased little and came to a plateau while light/dark frequency surpassed 10 Hz. Light integration effect showed that the best result one can expect by applying intermittent illumination to microalgae culture was to achieve the light efficiency under continuous illumination of the diluted light intensity (k*I). This light efficiency could be gradually approached by increasing light/dark frequency. Based on the above analysis, physiologically optimum light conditions for microalgae could be obtained, that is, the product of light intensity and light fraction (k*I) algal cell experienced falling into the light-limited region of the algae species, and light/dark frequency exceeding 10 Hz. This can be used as a comprehensive method for photobioreactor design and scale-up. Concerning the implementation of the above light conditions in reactor, this work, being different from previous ways of intensifying turbulence through inner structure, tried to use optical fibers being reasonably arranged inside reactor as the inner light source to create spatially ordered light regions and dark regions, and control flowing direction and velocity of the culture to give desired light/dark cycles, and then to fully fulfill FLE of microalgae. Based on this idea, the work carried out design and operation calculation for optical-fiber photobioreactor possessing FLE of microalgae, and then conceptively composed three types of reactors which could fully fulfill microalgae’s FLE, that is air-driven flat-plate photobioreactor, pump-driven flat-plate photobioreactor and fermenter-type photobioreactor. Their common feature is that the flowing direction is vertical to optical fibers. Based on the above schematic design, a pilot scale (130 L) airlift flat-plate optical-fiber photobioreactor was designed and constructed. The method of arranging optical fibers on a number of modules effectively avoided possible problems of high risk of leakage, complicated installation and unfriendly usage, caused by digging holes on reactor walls to stabilize optical fibers. Cold model test proved its good performance in light distribution, gas-liquid mass transfer and light/dark cycling. Cultivation of Spirulina platensis and Scenedesmus dimorphus was then carried out in the reactor, showing that the growth rate and light efficiency of optical-fiber photobioreactor were 38% and 28% higher than that of airlift photobioreactor, respectively, under the same volumetric light energy input. The light efficiency of optical-fiber photobioreactor (7.1%) was 3.8 times, 2.7 times and 1.3 times of that of outdoor tubular, flat-plate and column photobioreactors, respectively, while cultivating Scenedesmus dimorphus. The results showed the feasibility and effectiveness of the design method based on fully fulfillment of microalgae’s FLE in photobioreactors. Based on the above results, conceptive design and productivity estimation of large scale optical-fiber photobioreactor system were carried out, showing that higher light efficiency could be acheived with lower energy cost, and its productivity was higher than that of traditional enclosed photobioreactors.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ipe.ac.cn/handle/122111/1754
Appears in Collections:研究所(批量导入)_学位论文

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Recommended Citation:
薛升长. 基于微藻闪光效应的光生物反应器设计方法[D]. 中国科学院研究生院. 2011.
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