| Control of CO2 levels within certain range is one of the most important tasks in life support systems, such as spaceship and submarine. Techniques used for CO2 removal from the closed space require high efficient, safe and reliable CO2 extraction systems characterized by small volume, low mass. lowr rate of energy consumption, minimal use of consumables, and little or no crew time for operation and maintenance. In this work, cell photosynthetic biofixation and catalytic conversion were used to remove low concentration CO2. The former method introduced the photosynthesis of Chlorella vulgaris. The other one applied cell (Escherichia coli) surfaced displayed carbonic anhydrase (CA) as catalyst in contained-liquid membrane. Mainly research of the thesis includes the following five aspects:1. A membrane photobioreactor with a hollow fiber membrane module integrated inside was designed for CO2 removal by C. vulgaris cultivation. The design of this novel reactor took light availability into account, and it applied membrane technology to strengthen the gas-liquid mass transfer rate. The effects of gas flow rate, light intensity and quality, characteristics of membrane module on CO2 fixation were investigated. Performances of the presented bioreactor, a draft tube airlift photobioreactor. a bubble column and a membrane contactor, were compared.2. A membrane-sparged helical tubular photobioreactor (MSTR) was designed in this study. Mass transfer coefficients, mixing intensities and capabilities of CO2 biofixation through the photosynthesis of C. vulgaris in MSTR under different gas, liquid flow rates and light intensities were compared with two other photobioreactors (BCTR and MCTR). BCTR took a perforated pipe as sparger, while MCTR employed a membrane contactor as the whole mass transfer system. To establish if the limitation of CO2 removal was improved in MSTR. pH, dissolved oxygen, cell damage, and characteristic times for mixing, mass transfer and CO2 consumption were analyzed. 3. To obtain high performance of CO2 removal by C. vulgaris. establishing a kinetic model of microalgae growth becomes important, because an accurate model is a prerequisite for designing an efficient photobioreactor, and optimizing operating conditions. A mechanistic model based on Eilers & Peetrs'was proposed to predict the productivity of C. vulgaris, and it can help us achieve a quantitative understanding of how the performance is affected by light irradiance, pH and dissolved oxygen (DO).4. The expression of CA from Helicobacter pylori on the outer membrane of E. coli using a surface-anchoring system derived from ice nucleation protein (INP) from Pseudomonas syringae was developed. Two kinds of parent vectors were used to construct the fusion genes, and for each vector, three recombinant strains, each expressing a different length of the fusion protein, were obtained. SDS-PAGE, two-dimensional electrophoresis, Western blot, immunofluorescence microscopy, FACS. and whole-cell ELISA confirmed expression of the fusion proteins. CA activity, growth kinetics, outer membrane integrity, thermal stability, and protease accessibility were analyzed to determine the optimal length of anchoring motif and the preferred plasmid promoter.5. Design of hollow fiber membrane reactor and study of low concentration CO2 removal. The membrane reactor was constructed by two independent sets of intimately commingled hydrophobic microporous PVDF hollow fibers containing cell surface displayed CA. The effects of gas flow rate. CA concentration. pH and stability were investigated. |
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