| Summary: | 碩士 === 國立成功大學 === 環境工程學系碩博士班 === 96 === In order to mitigate global warming, it’s important to reduce CO2 emissions in the world. In this study, we simulate a flue gas with CO2 to be absorbed in a scrubber, and produce NaHCO3 to grow algae. Some studies suggest marine microalgae have higher photosynthetic efficiencies that can solve the global warming problem. When algae grow in a nitrogen deficiency environment, they may produce more lipid or carbohydrate. Therefore, algae have the potential to be a useful bio-erengy.
The cultivation of marine microalgae MN41 under semi-batch or continuous culture in an 1L photo-bioreactor of this study were carried out at 30℃ and with a light intensity of 7,500 Lux. The operating parameters include nitrogen compound type, nitrogen nutrient concentration, carbonate concentration, and pH.
In the experiments of the effects of nitrate concentration on the lipid and carbohydrate contents of the biomass in a semi-batch process, the results show that μmax = 4.19 ± 0.36 d-1 and Ks = 0.03 ± 0.02 mM. The lipid content hits its peak value of 26.2% with a production rate of 299 mg/L/d when the initial nitrate concentration is 0.56 mM. The carbohydrate content reaches its peak value of 72.6% with a production rate of 700 mg/L/d when the initial nitrate concentration is 0.34 mM.
In a TA-Mass analysis, the biomass has a 70% weight loss at around 300℃. The biomass also generates more gases, such as CH4, H2O, CH3COOH, CO, CO2 and some high molecular weight gases, at this temperature. It generates the most amounts of the gases when the initial nitrate concentration is 0.56 mM. A large amount of CaCO3 is precipitated if OH- is over fed when the carbonate is supplied by bubbling of CO2 through the solution.
In the experiments of the effects of ammonium concentration on the lipid and carbohydrate contents of the biomass in a semi-batch process, the results show that μmax = 8.95 ± 0.96 d-1 and Ks = 0.06 ± 0.05 mM. The lipid content hits its peak value of 22.6% with a production rate of 321 mg/L/d when the initial ammonium concentration is 0.50 mM. The carbohydrate content reaches its peak value of 57.2% with a production of 723 mg/L/d when the initial ammonium concentration is also 0.50 mM. The growth performance of the MN41 is poor when it is cultivated with a urea culture.
From the above results, the nitrate was chosen for the continuous cultivation experiments. The carbonate and nitrate concentrations of the inlet medium were 5.54 and 0.24 mM, respectively, with a pH value of 6. The results show that the biomass maintains at 92~97 mg/L with a lipid content of 17.4% and a carbohydrate content of 37.2%.
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