生長與二氧化碳捕捉高效能微藻株之分離與特性分析

Abstract

全球暖化是現今世界各國所重視的議題之一，它是由於大氣中之二氧化碳（CO2）的逐漸增加所導致。而微藻具有非常高的光合作用效率，利用微藻行光合作用的生物固碳法是近年來二氧化碳減量技術中最經濟也最有潛力的方法，此外，微藻還可將二氧化碳轉換為微藻生物質，並累積油脂於藻細胞中，再經油脂萃取與轉脂化的方式將藻油轉化為生質柴油。 在本研究中，已經成功的篩選分離出兩株耐熱性微藻突變株：Chlorella sp. MT-7 和Chlorella sp. MT-15，這兩突變株養殖於亞熱帶地區的戶外密閉式光生物反應器時，無須冷卻系統即可耐受室外高溫並極具生長潛能，其中微藻突變株MT-15養殖於戶外炎熱的陽光直射下之光生物反應器時，反應器中培養液的平均溫度高達41 □ 1°C，突變株MT-15的比生長率卻仍可維持在0.238 d-1，而野生型Chlorella sp.的生長則明顯被抑制。 此外，為了最適化大型光生物反應器之培養條件，我們需考慮光生物反應器的照度和混合效率的變化，在本研究中，使用了垂直密閉式圓柱型之光生物反應器做為耐熱性微藻突變株Chlorella sp.生長和CO2固定效率最適化研究之反應器，並針對此反應器中多種不同的反應參數，如通氣量、夜間光源（T5 或 LED）、光生物反應器之角度和光生物反應器內之隔板等對生長和CO2固定效率的影響來進行研究，其中以通入5% CO2、通氣量10 L min-1、夜晚光源為LED燈培養時，能得到最佳的平均生長速率0.239 g L-1 d-1。當具有隔板之光生物反應器的傾斜角度為15°時，微藻的生長速率則有明顯的提升，CO2的固定效率也可以看到有顯著的增加。透過本研究將可評估如何建立一個高效能的戶外密閉式圓柱型之光生物反應器。

Global warming, which is due to the increasing carbon dioxide (CO2) level in atmosphere, is receiving considerable attention world-wide nowadays. Microalgae have the advantages of very efficient photosynthesis. Biological fixation using microalgal photosynthesis have emerged as a potential option and been known as an effective as well as economical CO2 reduction technology in recent years. Microalgae can convert CO2 to biomass, it can also accumulate lipid in microalgal cells. Lipids in microalgae can be extracted and converted to biodiesel fuel by the process of transesterification. In this study, we have isolated two thermal-tolerant mutant strains of microalgal Chlorella sp., MT-7 and MT-15, which can grow well in an outdoor closed photobioreactor under hot sunlight without the supply of cooling system in the area of subtropical region. In outdoor cultivation under hot sunlight, with the culture broth temperature within the photobioreactor which could go up to average of 41 □ 1°C, the mutant strain MT-15 grew with the specific growth rate of 0.238 d-1. Whereas, the growth of wild type was inhibited in the outdoor cultivation. Besides, both mutant strains could grow faster under high-density and also remove the CO2 with significantly higher CO2 fixation rate than the wild type does. In addition, for the optimization of photobioreactor in large scale cultivation, the changes in illumination and turbulence of photobioreactors are needed to be taken into consideration. In this study, we have used vertical enclosed column photobioreactor to investigate the optimum conditions for the growth and CO2 fixation efficiency of a thermal-tolerant mutant strain of Chlorella sp.. This is the first report that multiple effects, such as aeration rate, light supply (T5 or LED) during nighttime, inclination of photobioreactor and baffles inside photobioreactor has been studied. With 10 L min-1 aeration of 5% CO2 and the supply of LED light during the night, the highest average growth rate of culture was achieved (0.239 g L-1 d-1) in this study. When the photobioreactors with baffles were set up at 15°, the microalgal growth rate was significantly increased and the CO2 fixation efficiency was also increased. Through this study, a high performance of outdoor cultivation in the enclosed column photobioreactor was evaluated.