| Microalgae are regarded as one of the most prospective candidates to solve the present energy and environmental issues. Currently it appears that the production of microalgal bioenergy is limited by high culture cost and low production efficiency. To promote the R&D of microalgal bioenergy, extensive attention should be paid not only on the screening of excellent microalgal species, but also on the improvement of microalgal lipid production efficiency. Microalgal cultivation coupled with biofixation of CO2 is a widely recognized way to reduce bioenergy production cost. NOx and SOx present in flue gas further complicated the issues.In this thesis, a series of experiments were conducted to investigate the effects of simulated flue gas (15% CO2,0.03% SO2,0.03% NO, and balance N2) on the growth and lipid accumulation of Chlorella pyrenoidosa XQ-20044. The growth and carbon sequestration features of a carbohydrate-rich microalga Scenedesmus sp. KM17 were also evaluated using both indoor and outdoor cultures. Besides, plant growth regulator GA3 was used and tested in C. pyrenoidosa XQ-20044 to promote microalgal lipid production. These efforts have aimed to couple microalgae bioenergy production with biofixation of carbon dioxide from flue gas. The main conclusions were as follows:1. With the strategy of intermittent injection of flue gas by automatic pH feedback control, an integrated lipid production, CO2 fixation, and SO2/NO removal by Chlorella was preliminarily established, which not only relieved the toxicity of flue gas to the microalgae, but also enhanced the efficiency of flue gas biofixation. Under batch-culture conditions, SO2 and NO in typical flue gas (containing 15% CO2,0.03% SO2,0.03% NO) can be used by C. pyrenoidosa XQ-20044 for the growth and lipid accumulation. However, SO2 from the flue gas only meet 25% of total sulfur demand, NO from the typical flue gas only meet approximately 2% of total nitrogen demand. So addition of extra S and N source is required. On the other hand, a lipid content of 38.0% DW was achieved in C. pyrenoidosa XQ-20044 in 6-day culture with the simulated flue gas. What’s more,81.2% of total lipid was neutral lipid, and C16, C18 were the most abundant fatty acids (99.5%), and the ratio of saturated fatty acids plus monounsaturated fatty acids in the microalgal lipid was 74.5%. In addition,95.9% of CO2,100% of SO2 and 84.2% of NO were removed by the microalgal culture. These results suggested that C. pyrenoidosa XQ-20044 could efficiently fix flue gas for lipid production.2. Both the growth and lipid accumulation of C. pyrenoidosa XQ-20044 were influenced by initial NaN03 concentration, and 2.35 mmol/L was the optimal initial NaN03 concentration in the "batch stage" of semi-continuous culture of C. pyrenoidosa XQ-20044. The semi-continuous culture of C. pyrenoidosa XQ-20044 was realize under all experimental combinations of NaN03 supplementation rate and the renewal rate of medium. Both initial NaN03 supplementation rate and the renewal rate had significant effects on the biomass productivity, lipid content and lipid productivity of C. pyrenoidosa XQ-20044. When NaNO3 supplementation rate was 0.12 mmol/(L·d) and the renewal rate was 30.0% simultaneously, the maximum lipid content of 38.0% DW, was achieved, which was significantly higher than that of the other treatments (p<0.05). The maximum lipid productivity [45.5 mg/(L·d)] was also obtained. The biomass productivity, lipid content and lipid productivity of C. pyrenoidosa XQ-20044 cultured with the simulated flue gas reached 0.17 g/(L·d), 30.8% and 51.9 mg/(L·d) respectively, and the removal rates of CO2, SO2 and NO in the simulated flue gas were 94.8%,100%,91.9%, respectively. Moreover, compared with the batch culture, little difference had been observed in the fatty acid composition of semi-continuous culture, but the biomass productivity, lipid productivity and CO2 fixation rate increased by 23.3%,9.6% and 23.3% respectively.3. Plant growth regulator GA3 enhanced both microalgal growth and lipid accumulation by stimulating esterase activity and regulating intracellular carbon distribution. The maximum lipid content (29.2%) and lipid productivity [17.1 mg/(L·d)] were achieved at 20 mg/L GA3. The main fatty acid were C16 and C18 which accounted for more than 91.5% of the total fatty acids at 0.1～20 mg/L GA3. Moreover, higher GA3 concentrations (10 and 20 mg/L) increased unsaturated fatty acid content significantly (1.6 times).4. When cultured in column photobioreactor indoors for 8 d, the biomass dry weight (DW) of Scenedesmus sp. KM 17 was 1.53 g/L with 8.9% as protein,20.6% as lipid and 39.8% as carbohydrate; the biomass productivity, CO2 fixation rate and carbohydrate yield were 172.5 mg/(L·d),310.5 mg/(L·d) and 71.5 mg/(L·d), respectively. When cultured in tank photobioreactor outdoors for 12 d, the protein content, lipid content and carbohydrate content of the alga were 6.9%,15.5% and 48.7% DW respectively; the biomass productivity, CO2 fixation rate and carbohydrate production rate reached to 56.7 mg/(L·d),102.1 mg/(L·d) and 27.8 mg/(L·d), respectively. When cultured outdoors in 5 m2 open raceway pond, the protein content, lipid content and carbohydrate content of the alga were 11.8%,12.7% and 45.0% DW respectively; the biomass productivity, CO2 fixation rate and carbohydrate production rate were 67.5 mg/(L·d),121.5 mg/(L·d) and 30.5 mg/(L·d), respectively. When Scenedesmus sp. KM 17 was cultured with the simulated flue gas under pH automatic control, the biomass productiviy was 0.14 g/(L·d) and carbohydrate content was 48.7%. Besides, removal rates of CO2, SO2 and NO were 94.5%,100% and 98.5%, respectively. The present study showed that Scenedesmus sp. KM 17 was an excellent strain with desirable characteristics of fast growth, high carbohydrate content and anti-contamination, which could be suitable for outdoors large-scale cultivation. The results also indicated the potential of Scenedesmus sp. KM 17 to growth with flue gas and produce carbohydrate production, which is a bioethanol feedstock.This study preliminarily established a model of integrated lipid/carbohydrate production, CO2 fixation, SO2/NOX removal by microalgae, which provided novel approaches for utilization of flue gas as carbon source to produce bioenergy from microalgae. In addition, the lipid production capacity of C. pyrenoidosa XQ-20044 was improved by GA3 treatment, providing new technical way for the research and development of microalgal bioenergy. This study is of great importance for bioenergy production and environmental pollution treatment. |
PDF Full Text Request