| 摘要: | 小球藻 (Chlorella) 相較於陸生產油作物如棕梠、痲瘋樹、大豆和油菜籽而言，小球藻具有較高的含油量且較短的生長時間，因此小球藻乃生質柴油料源之首要選擇。 小球藻 (Chlorella) 和 酵母菌 (Saccharomyces cerevisiae) 混合培養是一種創新的發酵策略，和傳統式微藻單一培養相比較，小球藻 (Chlorella) 和 酵母菌 (S. cerevisiae) 混合培養不僅可增加二氧化碳固定效率同時增加油脂產量。 小球藻 (Chlorella) 和 酵母菌 (S. cerevisiae) 混合培養主要是一種共生關係，經由實驗結過顯示，細胞乾重和油脂含量相較於微藻單一培養分別增加128.1 % 和165.2% 達1884 mg L-1 和358 mg L-1 。在不同光強度實驗中，光強度範圍介於1000 lux到8000 lux，光強度對混合培養下細胞生長和產物生成之影響非常顯著，且不同的光強度有不同的影響；最適合細胞生長的光強度為5000 lux，而8000 lux下具有最佳之單位生物質量對產物之轉化率。同時，共培養的二氧化碳固定速率可達到64.76 mg L-1 h-1和導入空氣且單一培養之小球藻 (Chlorella) 實驗結果相比較可提升195 %。在生質柴油品質分析部分，利用混合培養所生產之生質柴油具有較低之不飽和度，相較於微藻單一培養之生質柴油品質，混合培養之生質柴油具有較高品質之氧化穩定性和點火延遲時間特性。 在文獻上，不論是單一培養或混合培養，光品質對於微藻生成油脂的影響都相當的模糊不一致，本研究利用不同光波長和強度之LED光生物反應器用以提出具成本效益的油脂生產操作策略。在不同光條件下，小球藻 (Chlorella) 和酵母菌 (S. cerevisiae) 混合培養之油脂產量均高於單一培養之油脂產量。在光品質對混合培養的實驗結果指出，最適合Biomass生長的光波長和強度分別為紅光1000 lux，而最適合油脂生成的光條件則是藍光1000 lux。由於發酵條件上的差異，本研究提出一種創新二階段LED光操作策略，實驗結果得到了最佳的產物濃度和產率分別為261 mg L-1和8.16 mg L-1 h-1。兩階段光控制發酵程序相較於藍光1000 lux培養其產率可提升96 %，相較於紅光1000 lux培養其產率可提升10 %。本研究成功得證明使用創新的二階段LED光操作策略進行混合培養實驗可達到最佳的微藻生產油之效益。 相較於微藻修飾瓦因培養基 (modified Walne’s medium)，廢棄魚內臟水解培養基 (fish waste hydrolysate, FWH) 運用在微藻生產油脂上更具經濟效益。利用廢棄魚內臟水解培養基作為混合培養之營養源其最佳之最佳產物濃度和產率分別為1154 mg L-1和20.61mg L-1 h-1，和微藻修飾瓦因培養基相比較，其分別增加222 % 和176 %。考量低成本的優點，廢棄魚內臟水解培養基將是個具發展潛力的營養源同時亦可取代商業複合培養基，此外，廢棄魚內臟水解培養基也兼具環保特性。 Chlorella strains as compared to terrestrial oil crops such as palm, jatropha, soybean and rapeseed having higher oil content and shorter generation time have been considered as the promising candidates for alternative biodiesel. Mixed culture of Chlorella sp. and Saccharomyces cerevisiae was proposed as a novel strategy for enhancing CO2 biofixation rate and oil formation as compared with the traditional monoculture of microalgae. A symbiotic relationship was observed between S. cerevisiae and Chlorella sp., resulting in the improvements of cellular biomass and oil accumulation reached 128.1 % and 165.2 %, respectively. Influence of light intensity ranging from 1000 to 8000 lux on the cell growth and product formation of the mixed culture was significant but different; the optimal light intensity for cell growth was at 5000 lux, but the highest specific product yield was at 8000 lux. The CO2 biofixation rate of a mixed culture reached 64.76 mg L-1 h-1, which was 195 % improvement as compared to that of the monoculture of Chlorella sp. aerated with air. The biodiesel from the mixed culture would show low degree of unsaturation (71.74), resulting in better quality in terms of oxidative stability and ignition delay time property as compared to those from the monoculture. Since the influence of light quality on oil formation of microalgae in either monoculture or mixed culture in literature was either inconsistent or ambiguous, a light-emitting diode (LED) photo-bioreactor with different light sources and intensities was used in this study to propose a cost-effective lipid production process. The oil accumulation in a mixed culture of Chlorella sp. and Saccharomyces cerevisiae was higher than that of the monoculture in spite of different light sources used. Results of the influence of light quality on the mixed culture indicated that the optimal light wavelength and intensity for biomass formation was red LED light at 1000 lux, whereas the optimum for oil formation was blue LED light at 1000 lux. A novel two-stage LED photo-bioreactor was thus proposed and the highest Pmax and productivity in this section were obtained as 261 mg L−1 and 8.16 mg L−1 h−1, respectively. The improvements of the productivity of the two-stage light control fermentation process over the cultures of blue LED light and red LED light under 1000 lux were 96% and 10%, respectively. A novel two-stage LED photo-bioreactor of a mixed culture was proposed to optimize microalgal oil production and successfully demonstrated in this study. Compared with the modified Walne’s medium, the fish waste hydrolysate (FWH) medium had more efficiency in biodiesel production. The highest product concentration and productivity in this section were obtained as 1154 mg L−1 and 20.61 mg L−1 h−1, respectively. The improvement of product concentration and productivity of FWH medium condition were 222 % and 176 %, respectively, as compared with Walne’s medium condition. Considering its low-cost, FWH medium could be a potential nutrient and a substitute for commercial complex medium, with an environmental solution in addition. |
