博士 / 國立臺灣大學 / 農業化學研究所 / 89 / Increased concentration of carbon dioxide in the atmosphere is considered to be one of main causes of global warming problem. Among various approach methods for CO2 reduction, biological CO2 fixation by microalgal photosynthesis has been proposed as an economically feasible method. To investigate the biological fixation of carbon dioxide, more than 200 microalgae isolates were screened from the lakes, ponds, sediments, hog wastewater, paddy fields, hot spring and seawater in Taiwan. Two unicellular microalgae, isolates NTU-15 and NTU-H25, isolated from hog wastewater and had high growth rate at high concentration of carbon dioxide. They grew in air containing CO2 up to 40% and had growth rate 0.21 g /L/day at 40% carbon dioxide. They could grow at 39℃and the growth rate increased from 30 to 35oC. Both algae had the same growth rate in the range from 5 to 40% CO2 and had the similar light response between 2,000 and 6,000 Lux. Isolate NTU-H15 was higher growth rate than that of isolate NTU-H25 at pH 4.0 and ³ 35℃. Isolate NTU-H15 could tolerate high concentration CO2, high cell density and a broad-range of growth temperature and pH. It is suitable for large-scale cultivation to fix carbon dioxide. Each liter of isolate NTU-H15 produced 1.8 g of dry cell, and the growth rate was 0.22 g/L/day at 15% CO2. When air-grown cells of isolate NTU-H15 was enriched with CO2, growth was enhanced after a lag period of one to two days at 20% CO2, and 3 to 6 days at 40% CO2. Changes in the rate of photosynthesis measured as oxygen evolution was similar to those observed for growth. When low-CO2 cells were transferred to 40% CO2, pH in the culture medium dropped to 5.3. However, the result indicated that inhibition of photosynthesis and PSII activity were not the result of the low external pH but due to high-CO2 concentration. In isolate NTU-H15, carbonic anhydrase (CA) was almost localized on the cell surface. The cells grown in 5%CO2 had more CA activity and photosynthesis. However, the activity of RuBisco was not significant difference between 20% and 40% CO2 grown cells. To identify 3 high-CO2 tolerant isolates NTU-H15, NTU-H25 and NTU-H47, they were identified by PCR techniques to analysis the nuclear-encoded, chloroplast-encoded small-subunit rDNA sequence and biochemical properties. All of them were unicellular and the cells were spheroids 3-6 mm in diameter. Each cell had one cup-shaped chloroplast with a distinctive pyrenoid. Chlorophylls a and b were detected. The isolated strains were mainly attributed to Chlorella sorokiniana, one of most common species of green algae growing in around 35℃. Phylogenetic analysis showed relationships among 3 isolates were closed to each other and closed to C. sorokiniana. From the morphological, biochemical and phylogenetic analyzed, 3 isolates might be belong to C. sorokiniana. A 70L flat-photobioreactor was developed to achieve high growth rate of Chlorella sp. NTU-H15 and reduce CO2 emission. Chlorella sp. NTU-H15 was cultivated under various light intensities. Light intensity affected the algal growth and CO2 concentration in the exit gas. The final biomass was dependent of light intensity and was limited by phosphate concentration in the medium. The maximal growth rate and biomass were 0.38 g/L/day and 1.84 g/L in the 70L reactor, respectively. In the linear growth phase of isolate NTU-H15 cultivated in this reactor, the CO2 concentration in the exit gas ranged 12.5~13.5 % when 15% CO2 was introduced into the photobioreactor. Cell components of Chlorella sp. NTU-H15 is both enriched in protein (50%), included 8 kinds of essential amino acids and linoleic acid (25%) in the fatty acid. The isolated microalgae could grow at high temperature, high CO2 concentration and high cell density, therefore, biological CO2 fixation might be an economical and potential method in the future, and flat-photobioreactor is useful for high-density cultivation of Chlorella sp. NTU-H15 and biological CO2 fixation in a large scale.
| Identifer | oai:union.ndltd.org:TW/089NTU00406027 |
| Date | January 2001 |
| Creators | Ed-Haun CHang, 張義宏 |
| Contributors | Shang-Shyng Yang, 楊盛行 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 309 |
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