【作者】 李永富；

【导师】 孟范平；

【作者基本信息】 中国海洋大学 ， 环境科学， 2014， 博士

【摘要】 面对严峻的全球变暖和能源危机形势，利用微藻高效固定CO2并耦合生物柴油生产因具有明显的应用价值和环保效益，受到研究者的广泛关注。目前，该技术的瓶颈之一是开发高效节能的封闭式光生物反应器（PBR）。本论文以封闭式PBR中微藻高效固定CO2为研究目标，从前期获得的四种微藻中选定普通小球藻(Chlorella vulgaris)作为CO2固定与转化的高效传递载体，基于平板式PBR占地面积小、气液传质效果好、易于放大、结构简单等优势，在其中内置LED光源以提高能量产出率，历经两次结构改进，研制了新型的竖直放置气升式内环流平板光生物反应器(ILA-PBR)，用于固定高浓度CO2(15%CO2)。（1）适于微藻生长的光源选择。以前期筛选的具有耐高温、耐高浓度CO2和耐酸性环境特性的普通小球藻(Chl. vulgaris)、盐生杜氏藻(D. salina)、纤细角毛藻(Cha. gracilis)和温泉6#藻(Cy. aponinum)为研究对象，用摇瓶培养方法进行了适宜4种微藻生长的人工光源及光质比选。在柔性红光LED灯带(LED-R)、柔性蓝光LED灯带(LED-B)、柔性白光LED灯带(LED-W)和荧光灯(FL)四种人工光源提供的不同光质照射下，以LED-W最适于普通小球藻、盐生杜氏藻和温泉6#藻生长，而LED-B最适宜纤细角毛藻生长。微藻生长所需的光质条件存在种质差异性，4种微藻的最适光质条件是普通小球藻LED白光（LW）或LED白光+LED蓝光（LW+LB），纤细角毛藻LED蓝光(LB)或FL白光+LB(FW+LB)，温泉6#藻LED白光+LED红光(LW+LR)；而盐生杜氏藻的生长受光质调控不明显。由此认为柔性LED灯带比FL具有更大的应用优势。（2）反应器中4种微藻的固碳产油潜力比较及人工光源确定。构建了第一代ILA-PBR，在通气条件下进行4种微藻的批次培养，微藻对不同浓度CO2有不同的生长响应。微藻生长的最适CO2浓度分别是：普通小球藻（1%~2.5%）、盐生杜氏藻（1%~2.5%）、纤细角毛藻（1%~5%）和温泉6#藻（0.04%）。以最大固碳速率(FD)、基于总脂的能量产出率(ERoil)、油脂产率(LP)为评价指标对4种微藻进行比选，确定普通小球藻固碳产油潜力最大，FD最大值出现在通入1%浓度CO2条件下，为1.18gCO2L-1d-1；最大ERoil和LP分别是盐生杜氏藻、纤细角毛藻、温泉6#藻的4.5倍、4.6倍和21倍。对适于普通小球藻生长的两种光照条件(LED-W和LED-W+LED-B)进行实用性检验发现，藻细胞在两种光源下生长情况接近，但在LED-B的灯管上微藻附着生长现象严重，因此，以LED-W作为普通小球藻的内置光源较为合适。（3）反应器构筑参数优化及光强、CO2浓度对固碳效果的影响。以普通小球藻作为受试藻种，对第一代ILA-PBR进行构筑参数优化。正交试验表明，在采用导流管并进行内部双侧光照条件下，当高径比(H/D)为6:1，降流区与升流区的面积比(Ad/Ar)为3:1，表观气速(SGV)为0.3vvm时，ILA-PBR中的普通小球藻对CO2有最大固定速率。按SGV=0.3vvm通入体积浓度1%的CO2利于普通小球藻快速增殖。在增大初始接种光密度至OD680=0.5的同时提高入射光强至240μmol m2s1，可显著提高微藻对高浓度CO2的固定能力。1%CO2中微藻的FD为1.97gCO2L-1d-1。同样条件下，通入浓度15%的CO2后，FD可达1.00gCO2L-1d-1。（4）降低进气中O2浓度和改变培养模式对微藻固碳效果的影响。向ILA-PBR中通入含低氧的CO2气体，微藻FD能继续提高。配制1%CO2并降低进气中O2含量低于2%(v/v)，最大FD由1.97gCO2L-1d-1提升至2.27gCO2L-1d-1；通入低氧的5%CO2，最大FD由1.41gCO2L-1d-1提升至2.12gCO2L-1d-1，低氧进气方法对微藻固定CO2的促进效果明显。低氧进气条件下开展的微藻培养模式研究表明，半连续培养模式利于维持ILA-PBR中普通小球藻生物固碳的持续高效性。运行期间，除了第1d的FD为1.41gCO2L-1d-1外，其它时间的FD均能保持较高水平（1.77~2.42gCO2L-1d-1）。（5）改变通气方式的新型反应器固碳效果及能量产出分析。采用“数目放大”方法，与通气方式转变相结合，对ILA-PBR进行再改进，构建了第三代ILA-PBR。通入模拟烟气(15%CO2)，混合曝气方法比间歇通气方法所需的工程设备更为简洁，空气+15%CO2通入条件下，FD为1.46gCO2L-1d-1，进行低氧处理后(N2+15%CO2)，FD更高，稳定在1.79gCO2L-1d-1左右，分别比直接通入15%CO2提高了46%和79%，固碳性能优于现有报道中绝大多数封闭式PBR。从节能角度，在ILA-PBR中采用内置LED-W光照模式，与传统的FL外置光源模式相比可节能73.6%。前一光照模式下普通小球藻的ERoil为0.011，而后者仅为0.002，LED-W具有明显的节能优势。利用第三代ILA-PBR培养普通小球藻，在半连续培养模式下通入模拟烟气，基于微藻生物质的能量产出率（ERbiomass）和ERoil分别为0.0219~0.0249，0.0091~0.0104，亦高于大多数其他类型的PBR。结合FD的比较结果，认为本研究提出的第三代ILA-PBR具有高效节能特性，有望成为微藻固定工业烟气CO2的理想设备。更多还原

【Abstract】 Fossil fuel combustion is also the major source of greenhouse gases responsiblefor global warming. Renewable, carbon neutral, economically viable alternatives tofossil fuels are urgently needed to avert the impending oil crisis and the dramaticconsequences of climate change. At present, the potential value of microbial, andparticularly microalga, photosynthesis to fix CO2in industrial flue-gas and productbiofuel is widely recognized. Photobioreactors (PBR) are the critical equipment in thebiofuels from microalgae process, and are one of technical bottlenecks. Actually,studies have shown that well-designed cultivation systems may lead to significantincrease of CO2fixation efficiency. In this work, Chlorella vulgris was selected fromfour microalgae strains which has the characteristic of resistance for high temperature,high concentrations and low pH value as the CO2fixation and transformation carrier.Based on the advantages of Flat-plate photobioreactors in small occupied area, highmass transfer efficiency, simple structure and easy to scale-up, an innovative closedPBR called internal loop airlift flat plate photobioreactor equipped with interior LEDilluminant (ILA-PBR) was developed. Twice improvements were carried to increasedaily CO2fixation (FD) of Chl. vulgris with low energy consumption from simulatedflue-gas.The first step in developing an algal process is to choose the algal species. Fourstrains of microalgae mentioned in the former part, namely, Chlorella. vulgaris,Dunaliella salina, Chaetoceros gracilis and Cyanobacterium aponinum were studiedin batch mode. Artificial light sources were fluorescence lamp (FL), andflexchromatic light-emitting diode strips of red (LED-R), white (LED-W), and blue(LED-B). Nine light qualities, respectively, LED red light (LR), LED blue light (LB),LED red plus LED blue light (LR+LB), LED white light (LW), fluorescent white light (FW), and the proportions of red or blue light are increased in LW and FW (FW+LR,FW+LB, LW+LR, LW+LB) were provided. Results revealed that LED-W increasedthe maximum photosynthetic action rate of Chl. vulgaris, D. salina, and Cy. aponinum,homoplastically, LED-B played the same role in the growth of Cha. gracilis. In termsof the light qualities, the present data showed species-specific photoacclimationresponses for four species. At the irradiance of60μmol m2s1, the growth rate ofChl. vulgaris was significantly higher under LW and LW+LB than under the otherlight treatments. The highest growth rate of Cha. gracilis appeared under the lightqualities LB or FW+LB. LW+LR was the most favorable for the growth of Cy.aponinum. Be different than other strains, the growth rate of D. salina did not changedistinctly with light qualities. Whatever the light resource and the light quality, theflexible LED strips have more advantages than FL for microalgae growth.To investigate the suitable conditions of CO2supply, the first generationILA-PBR with3.2L of working volume was built. In the microalgal cultures aeratedwith0.04%,1%,2.5%,5%and10%CO2, the maximal FD in fed-batch mode of C.vulgaris was1.18g CO2L-1d-1with1%CO2aeration. The optimum CO2concentration for microalgae growth was, respectively, Chl. vulgaris1~2.5%, D.salina1~2.5%, Cha. gracilis1~5%, and Cy. aponinum0.04%. Uniformly, thelipid-based energy ratio (ERoil) and lipid productivity of Chl. vulgaris was3.5timeshigher than that of D. salina,3.6times higher than Cha. gracilis, and20times higherthan Cy. aponinum. Combined with the previous results, the practicability test of twokinds of light condition (LED-W, LED-W+LED-B) was carried out to explore thefeasibility of application. By comparing with the results obtained under the LED-Wlight, microalgae had similar growth pattern under the LED-W+LED-B light, however,Chl. vulgaris cells attached on the surface of LED-B seriously which might have anegative effect on biomass harvest. On the basis of that, the LED-W was suggested tocultivate C. vulgaris as an interior LED illuminant in ILA-PBR.Secondary, the growth and FD datas from Chl. vulgaris cultivated in theILA-PBR carried by orthogonal experiment were used to evaluate the effects of threemain design parameters including superficial gas velocity (SGV), the ratio of height to diameter (H/D), and the ratio between downcomer and riser cross sectional area(Ad/Ar) on FD. The design parameters were optimized as follows: SGV=0.3vvm,Ad/Ar=3:1and H/D=6:1. It was also demonstrated that SGV played an active role forFD by increasing average gas holdup (g) of microalgae suspensions. Microalgaegrowth was influenced by multiple factors, and only considering reactor performanceascension through volumetric mass transfer coefficient (kLa) was not comprehensive;increasinggcould play a more important role. Aeration was supplemented with1%CO2, and a SGV of0.3vvm was the most beneficial condition for the rapid growth ofC. vulgaris in ILA-PBR. Increasing the initial inoculation optical density (OD680) to0.5, synchronously, improving the incident light intensity to240μmol m2s1couldsignificantly enhance the microalgal resistance to high concentrations of CO2andeffectively improve FD to1.97g CO2L-1d-1in the microalgal cultures aerated with1%CO2at SGV=0.3vvm. Under the same initial OD680and incident light intensity, themaximum FD of1.00g CO2L-1d-1occurred in the first generation ILA-PBR whenSGV was0.3vvm, CO2concentration was15%.In addition, SGV was maintained at0.3vvm. CO2was continuously added to theN2stream to decrease the O2content in the flow agitation. Through this method, FDcould be improved sequentially. In the microalgal cultures aerated with1%and5%CO2with low O2concentration, the maximal FD were increased to2.27g CO2L-1d-1from1.97g CO2L-1d-1,2.12g CO2L-1d-1from1.41g CO2L-1d-1, respectively. Asemi-continuous process was operated under these conditions. The FD was highest incomparison with those in the batch and fed-batch cultivation modes. The results ofFD obtained from semi-continuous mode were1.41g CO2L-1d-1on the first day, andmaintained at the level of1.77-2.42g CO2L-1d-1. Consequently, semi-continuouscultivation mode is conducive to maintaining the high CO2fixtation efficiency of Chl.vulgaris in the ILA-PBR.Finally, the number amplification method was adopted to realize the enlargementof ILA-PBR based on the improved ventilation modes. Mixing aeration mode was putforward to account for it. The third generation ILA-PBR with8.0L of workingvolume was built and simulated flue-gas (15%CO2) was bubbled into microalgae suspension. The FD of this method was1.46g CO2L-1d-1and1.79g CO2L-1d-1when air or N2mixed with15%CO2in ILA-PBR, respectively. Above all, these FDvalues are considerably higher than reported in the published literature for mostclosed photobioreactors. From the perspective of energy conservation, taking LED-Was internal illuminant could saving73.6percent energy than the traditional FLexternal light pattern. It is important to re-iterate that the ERoilof C. vulgaris underformer light pattern is0.011, which is also considerably larger than the latter one(0.002). In the third generation ILA-PBR, the biomass-based energy ratio (ERbiomass)and ERoilof was0.0219-0.0249and0.0091-0.0104, also higher than most PBR.Taking all the evaluation indexes (FD, ERbiomassand ERoil) into consideration, as amore efficient and energy saving CO2fixation system, the ILA-PBR could bepotentially applied in the area of microalgae culturing for industrial flue-gas CO2removal.更多还原