鍋爐廢氣中二氧化碳再利用於微藻Chlorella sp.之養殖 以生產具生物功效性之微藻生物質

Abstract

近年來，大氣中過量的二氧化碳（CO2）累積成為全球暖化的主因，微藻養殖可用於廢氣中CO2的減除，同時可生產微藻生物質以應用於生質料源、動物飼料添加物及健康食品開發等多重效能。利用燃燒天然氣之鍋爐來產製蒸汽或熱水，其廢氣為城市CO2重點排放源之一，本研究中使用鍋爐燃燒所產生之廢氣（約10% CO2與50 - 60 ppm NOX）進行微藻株Chlorella sp.的養殖，以期能降低CO2排放，並探討微藻生長效能、油脂產量及油脂成份組成，另外亦探討使用由鍋爐廢氣所生產之微藻生物質作為動物飼料添加劑之可行性，測試微藻生物質對於小鼠之餵毒性試驗 (feeding toxicity)，並進行對乙醯氨基酚（acetaminophen）所誘發之小鼠肝損傷修復性試驗。 在鍋爐廢氣利用的研究中，通入不同廢氣比例組成的氣體用以進行微藻養殖，在批次式7天培養實驗結果中顯示，以通入100%之鍋爐廢氣者具有最佳的微藻生長效率，其最大生物質產率為0.90 g/L/day，油脂含量為17.6%；不同的廢氣通氣速率亦對微藻的生物質產率產生影響，在0.2 vvm的通氣速率下微藻有最大的生物質產率，為1.00 g/L/day，且可累積18.0%之油脂含量；另外，微藻對於鍋爐廢氣中CO2移除效率，於通入0.05 vvm廢氣時，具有最大移除效率，約為80％。 養殖所得之微藻經回收破壁及乾燥處理後，用於進行小鼠餵毒性試驗，我們在小鼠飼料中分別添加1、5及10%（w/w）之微藻製品，經連續餵食四週後，不同微藻添加比例之飼料皆對小鼠肝臟與腎臟無毒性反應。接著，我們利用acetaminophen處理來誘導小鼠肝臟損傷，且同時分別餵食飼料中添加有1、2.5及5%（w/w）之微藻製品，餵食實驗進行8週後犧牲小鼠，檢測小鼠血清中丙酮轉氨基脢（glutamyl pyrubic transaminase; GPT）與麩草酸轉氨基脢（glutamyl oxaloacetic transaminase; GOT）含量、肝臟中丙二醛（malondialdehyde; MDA）含量及肝臟中超氧化物歧化酶（superoxide dismutase; SOD）與過氧化氫酶（catalase; CAT）抗氧化酵素之活性，實驗結果顯示，飼料中添加含有1%之微藻製品即可明顯降低肝損傷所誘發提昇之小鼠GPT、GOT及MDA含量，且肝臟中SOD與CAT活性也皆顯著提昇，此表示Chlorella sp.生物質具有小鼠肝功能修復之生物功效性。 綜上所述，本研究證實利用鍋爐廢氣進行微藻養殖，有利於微藻生物質生產且具有CO2減排之效用。此外，養殖所生產之微藻生物質對於小鼠肝損傷具有顯著修復之生物功效性，可應用於動物飼料添加劑或健康食品之開發。

Recently, the global warming is a phenomenon attributed primarily to the increase of the carbon dioxide (CO2) concentration in the atmosphere. Microalgal cultivation can be used for CO2 mitigation from flue gas and to produce microalgal biomass for the applications of developing animal feed additive or human health foods. The boiler combusted natural gas can produce steam or hot water, which is one of the CO2 emission sources in cities. In this study, we used the flue gas generated from boiler (about 10% CO2 and 50 - 60 ppm NOX) combusted natural gas for the Chlorella sp. culture to investigate the biomass productivity, lipid content and compositions and CO2 removal efficiency of Chlorella sp. cultures aerated with boiler flue gas. In addition, the biomass of Chlorella sp. culture aerated with boiler flue gas for being animal feed additive was investigated, including 28-day feeding toxicity study and the protection of acetaminophen-induced liver injury in mouse models. In the study of boiler flue gas utilization, the optimal biomass productivity and lipid accumulation of the Chlorella sp. culture were 0.90 g/L/day and 17.6% aerated with full boiler flue gas, and 1.00 g/L/day and 18.0% aerated with 0.2 vvm aeration rate of boiler flue gas in the batch cultures for 7 days, respectively. The CO2 removal efficiency from boiler flue gas was approximate 80% in the Chlorella sp. culture with 0.05 vvm of aeration rate. After collected the microalgal cells, broken down the cell wall and dried the microalgal biomass from the culture, the Chlorella sp. product from the culture aerated with boiler flue gas was used to investigate the feeding toxicity study in mice. The mice fed with 1, 5 and 10% of Chlorella sp. product (w/w) for 28 days showed no hepatotoxicity and renal toxicity. Moreover, the mice were administrated acetaminophen to induce liver injury, fed with 1, 2.5 and 5% of Chlorella sp. product (w/w) for 8 weeks and sacrificed to determine the levels of glutamyl pyrubic transaminase (GPT) and glutamyl oxaloacetic transaminase (GOT) in serum, malondialdehyde (MDA) content and the antioxidative activities of superoxide dismutase (SOD) as well as catalase (CAT) in the liver. The results show that liver-injured mice fed with 1% of Chlorella sp. product could significantly decrease the levels of serum GPT and GOT and MDA content, and significantly increase the hepatic SOD and CAT activities. These results demonstrate the bioactive function of the Chlorella sp. product for liver protection. In summary, this study demonstrates that the boiler flue gas utilization in microalgal culture is benefic and potential for the production of microalgal biomass and the reduction of CO2 emission. In addition, the microalgal biomass is remarkable for the bioactive function on protecting liver injury and can be applied on developing the animal feed additive or human healthy food.