微藻養殖模式對微藻油脂含量與組成影響之探討

Abstract

近年來，隨著全球暖化與石化能源危機加劇，因此具有生產再生能源與減碳效益的微藻被視為主要綠色產業之ㄧ，而如何能有效發展微藻科技以達最大效益是目前各國積極研究的目標。本研究應用本實驗室已篩選出之生長快速與高油脂潛力的微藻株，小球藻(Chlorella sp.)與擬球藻(Nannochloropsis oculata)，利用自營培養至生長停滯期後加入不同碳源探討提升油脂產能之二階段微藻培養的可行策略。本研究所使用的Chlorella sp.與N. oculata藻株在提供全日光照培養下，其油脂含量在培養第20天時可分別達到42.6%與66.1%的最高量，其油脂產量則分別為0.38 g/L與0.78 g/L。本研究中的第一階段微藻培養皆為自營生長，此階段培養以獲得微藻生物質為目的，在養殖第8天，微藻密度達穩定狀態下，進入第二階段的異營或混營培養，此即在培養液中分別添加1%(w/v)的葡萄糖、蔗糖或糖蜜，並以提供二氧化碳或空氣者做為對照組。第二階段培養以短時間內（3天），可促進微藻油脂累積或改變油脂組成為目的。 在二階段皆於室內培養的實驗中，Chlorella sp.在第二階段添加蔗糖的混營培養下，微藻油脂產能最高，其油脂含量為41.4%，油脂產量為0.53 g/L。相似的結果也在N. oculata添加蔗糖的第二階段混營培養中顯示，其微藻油脂含量為60.6%，油脂產量為0.81 g/L，但是這些數值皆與對照組之微藻油脂和油脂產量相近。本實驗結果顯示，Chlorella sp.與N. oculata可透過二階段混營培養方式於較短時間內提升微藻生物質與油脂產量，但不影響油脂組成然而在第二階段為一營培養實驗中，結果顯示Chlorella sp.與N. oculata皆無法在葡萄糖、蔗糖及糖蜜作為碳源的情況下進行異營生長，此說明Chlorella sp.與N. oculata對光具有相當依賴性。在第一階段於戶外培養第二階段移置室內培養的實驗中，結果顯示Chlorella sp.在第二階段添加葡萄糖的混營培養下，微藻油脂含量約為24.3%，油脂產量為0.26 g/L，此較戶外Chlorella sp.長時間培養下油脂產量的0.14 g/L提升近一倍的油脂產能，因此應用戶外與室內二階段培養搭配以葡萄糖或蔗糖作為碳源進行混營培養，可於最短時間內達到較高微藻生物質與油脂含量。

In recent years, due to global warming and energy crisis, the low-polluted and renewable microalgal bioenergy industry is of great concern. How to improve the development of microalgal energy to achieve maximum beneficial result is the major goal all over the world. In this research, Chlorella sp. with high growth rate and Nannochloropsis oculata with high lipid content were selected as potential strains. In addition, two phase cultivation strategy was applied to enhance lipid production. In long-term phototrophic cultivation, maximum lipid content of Chlorella sp. and N. oculata can reach 42.6% and 66.1%, respectively. The lipid production of Chlorella sp. and N. oculata can reach 0.38 g/L and 0.78 g/L on the 20th day, respectively. In the two phase cultivation strategy, microalgae phototrophically grew and reached stationary phase as the first phase (8 days) cultivation for microalgal biomass production. The following 3 days of mixotrophic or heterotrophic cultivation after the first phase in the presence of either glucose, sucrose or molasses was as the second phase cultivation. The microalgal culture aerated with only CO2-enriched gas in the second cultivation phase was as the control experiment. The purpose of the second cultivation phase (3 days) was for enhancing the microalgal lipid accumulation or altering the lipid compsitions. In this study, the lipid production of indoor cultivation of Chlorella sp. which used sucrose as carbon source in mixotrophic cultivation can increase the lipid content to 41.4% and the lipid production was 0.53 g/L. There were similar results that the highest lipid content (60.6%) and lipid production (0.81 g/L) of N. oculata using sucrose as carbon source. Therefore, we demonstrated that Chlorella sp. and N. oculata are light-dependent for organic carbon source uptake and the two microalgal strains can not culture in heterotrophic mode while use either glucose, sucrose or molasses as carbon source. Chlorella sp. and N. oculata can culture by mixotrophic two phase cultivation strategy for increasing microalgal biomass and enhancing the lipid production in short time (3 days) without altering the lipid compsitions. In outdoor two phase cultivation, Chlorella sp. cultured outdoors during the first phase (8 days) followed by indoor cultivation (3 days) in mixotrophic or heterotrophic mode in the presence of either glucose, sucrose or molasses. The lipid content and lipid production of Chlorella sp. using glucose as carbon source can reach 24.3% and 0.26 g/L after the second phase mixotrophic cuitivation., The lipid production of Chlorella sp. using glucose as carbon source by two phase mixotrophic cultivation strategy can increase almost 2folds compared with the lipid production of outdoor long-term photoautotrophic cultivation of Chlorella sp.. Thus, microalgae culture by the two phase cultivation strategy, outdoor photoautotrophic cultivation (8 days) as the first phase combined with indoor mixotrophic cultivation (3 days) using glucose as carbon source as the second phase, can achieve higher microalgal biomass and lipid production.