| Summary: | 碩士 === 國立成功大學 === 環境工程學系碩博士班 === 94 === The global influence on climate changes of greenhouse effects, has already been paid attention to by the whole countries all over the world. In order to prevent our environment getting worse, the most important subject is to decrease the discharge of greenhouse gases. Though carbon dioxide does not contribute the most powerful greenhouse gas leading to greenhouse effect, it has the largest emission. Therefore, in all intensify parameter, cabon dioxide accounts for 55％. That is the reason why many researches focus on the decrease of carbon dioxide emission. In this study, we focus on the carboxylation for simulated absorbed solution from the alkaline wet scrubber with photosynthesis of algae under alkaline and thermal conditions.
The algae species was purified from hot springs and can thrive under alkaline and thermal conditions. To compare with spring algae, we take the sea algae, named Nannochloropsis oculata, from Fisheries Research Institute (Dung-gang Branch). The photo-bioreactor was designed by our laboratory, and it’s work volume is 1 liter. We use Na2CO3 to simulate carbon dioxide. The light intensity is 10,000 Lux, and always illuminate the reactor. We take different pH, temperature, concentration of carbon, and different carbon source as batch parameter in the experiment.
In “Free Culture” test, the growth of spring algae near to pH 12 is observed under 50℃ and sea algae goes to pH 9.7 under 25℃. As a result, we can understand the limitation of algae on alkaline condition. Then, the parameter of “Different pH Condition” test is set as pH＝7、9.5、11 (spring algae) and pH＝7、8.5、9.5 (sea algae). The growth of spring algae under steady pH＝11 was unapparent. It had maximal cell density 642 mg/L and the maximal growth rate of spring algae was 2.03 d-1. On sea algae culture, pH＝7 and pH＝8.5 had similar growth curve. The maximal cell density, appeared on pH＝7, had 425 mg/L, and maximal growth rate was 2.09 d-1.
In “Different Temperature Condition” test, spring algae cultured on 40, 55℃ and compared with 50℃. The max cell density has a little increase (709 mg/L), and the specific growth rate rise with temperature. The higher temperature we test, the larger specific growth rate (3.56 d-1), and higher utilization of carbon source can be observed. The relationship between temperature and substrate utilization can be expressed as ＝0.283(1.07)T-9.66. Sea algae can not surviv at 50℃, but it has similar maximal cell density and specific growth rate under 40℃. The maximal cell density is 394 mg/L and max growth rate is 1.97 d-1. It has the same situation on spring and sea algae, that is the higher temperature environment makes higher specific growth rate on algae.
In “Different Carbon Source” test, we bubble different concentration of CO2 gas as carbon source. The spring algae bubble 10％、20％、40％ CO2 gas (v/v) for experiment, and it can survive till 20％ CO2 after a 100 hours lag phase. The maximal cell density was observed more than 2,600 mg/L and the nitrate source become main limitation of algae growth. It has the same situation on sea algae. We bubbled air、5％、8％、10％ CO2 gas as sea algae carbon source. The maximal specific growth rate was observed on the parameter of bubbling air and it had 2.60 d-1. The limit of CO2 concentration was 8％, and a 36 hours lag phase was observed.
In “Different Initial Carbon (Na2CO3) Concentration” test, we focused on spring algae and set five different carbon concentrations. It was 0.5、1、3、5、10 g Na2CO3 per liter. We found the higher carbon concentration we added, the more max cell density we observed. We can get 1,505 mg/L cell density on 10 g experiment, and after adding additional light (10,000 Lux), we can even measure 1,693 mg/L cell density. From the result, we know that the limitation of high concentration carbon source experiment is light intensity. The maximal growth rate in this experiment was 2.95 d-1 and it was observed on 1 g/L concentration. We use “Monod equation” to simulate the relation of carbon concentration and specific growth rate, and we can get μmax＝1.666 d-1, Ks＝-12.388 mg/L.
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