| Summary: | 碩士 === 國立成功大學 === 環境工程學系碩博士班 === 101 === The concentration of carbon dioxide (CO2) has increased dramatically in earth’s atmosphere due to fossil fuels burning associated with increased population and industrialization. Therefore, the development of effective CO2 capture and storage technology is urgent and essential. Photosynthesis in microalgae and cyanobacteria has long been recognized as a suitable mean to sequester CO2. Light availability is an important factor for photobioreactor (PBR) design and operation, resulting in growth and CO2 fixation of microorganisms. Internally radiated PBR may maintain optimized light regime in each operation unit and is promising for scale up by increasing numbers of units. The light regime as flashing light in the PBR may enhance microalgae and cyanobacteria growth for increasing light utilization efficiency. Thus, the internally radiated PBR operated in flashing light was established.
In this study, the growth characteristics of cyanobacteria Arthrospira platensis (A. platensis) under various light conditions were investigated. We constructed an internally radiated bubble column PBR for A. platensis with LED light-dark flashing internally and fluorescent lamps illuminating externally: light intensities of fluorescent lamps were 460 μmol m-2 s-1 for high light intensity conditions and 360 μmol m-2 s-1 for low light intensity conditions; five LED light/dark fractions (k) were set to 1 (continuous illumination), 0 (without LEDs), 0.9, 0.8, and 0.7 at 1 Hz flashing. The specific growth rates (μ, d-1) under LED k = 1, 0.9, 0.8, 0.7, and 0 are 0.83, 0.44, 0.65, 0.45, and 0.35, respectively, at high light intensity conditions; 0.26, 0.24, 0.18, 0.21, and 0.23, respectively, at low light intensity conditions. The μ (d-1) under high light intensity condition with two LEDs at k = 1 and 0.8 are 0.79 and 0.59, respectively. Based on flashing effect theory, the specific growth rates indicate that there is no growth enhancement under LED light/dark flashing, which means there is no light integration enhancement. However, the biomass productivities under LED k = 1, 0.8, and 0.7 at high light intensity conditions show no differences, which are 0.24, 0.21, and 0.22 g L-1 d-1, respectively. The similar biomass productivities are obtained by applying LED light/dark fractions. The contents of C-phycocyanin (CPC) and carbon in dry A. platensis biomass show no differences under all light conditions, which are in average 9.6% and 54%, respectively. Therefore, the output of CPC productivity and carbon fixation rate is dominated by the biomass productivity. The CPC productivity at LED k = 1, 0.8, and 0.7 are 21, 20, and 22 mg L-1 d-1, respectively. The carbon fixation rate at LED k = 1, 0.8, and 0.7 are 0.48, 0.45, and 0.45 g L-1 d-1, respectively. The highest CPC productivity and carbon fixation rate are 22 mg L-1 d-1 and 0.48 g L-1 d-1, respectively. The CPC production and carbon fixation rate of A. platensis are maintained by the light/dark flashing. The cost saving by the light/dark flashing may be advantageous.
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