微藻相較於陸生植物具有較高的生物質生產力，且可利用電廠或工業煙道所排放之二氧化碳作為微藻生長所需的碳源，並可進一步應用於生產生質能源如生質柴油及生質油精等。因此應用微藻以進行固碳作用及生產生質能源(如生質柴油、生質酒精)在未來因應氣候變遷之對策具有相當潛力。然而，以生命週期評估觀點來看，從碳源供給微藻生長以至生產生質能源做一環境友善度之評估，了解其微藻養殖中所需之環境負荷如土地面積、營養鹽供給以及在製成生質能源之技術上如所需之化學及能源消耗等視為此研究必須關切的重點。
本研究目的主要應用生命週期評估以探討微藻生產生質能源這新興技術對於溫室氣體減量潛能評估，建立一套模式以估算其製程所需之化學、能源消耗、溫室氣體排放，以至改善不同製程了解其溫室氣體減量之潛能。
Nannochloropsis oculata為一含高脂質含量(高達50.4%）之藻類，選用於本研究中之藻種，採收後的微藻經油脂萃取程序得到脂質（三酸甘油酯），經轉酯化程序，將三酸甘油酯與醇類反應生成生質柴油，其所剩之殘渣約有55％之碳水化合物，其再經由發酵過程生產生質酒精。至今微藻生產生質酒精之發酵製程技術尚未有相當完整的資料，因此在該部份利用糖蜜及纖維素生產生質酒精之製程來估算其微藻生產生質酒精之能源消耗及溫室氣體排放之最大最小值，其原因在於微藻之碳水化合物為一聚醣類，其生產生質酒精之發酵技術必介於糖蜜與纖維素之中。除模擬推估溫室氣體排放量外，溫室氣體減量亦為本研究重點之一，利用化學溶液如已烷、苯等具有親水、親油性質之化學溶液萃取微藻之脂質來取代傳統油壓萃取法，以減少其能源消耗及溫室氣體之排放。
由於不同藻種具有不同之特性，如生長速率、藻密度、組成分（脂質、蛋白質及碳水化合物）等含量均不相同因而有不同之應用，故本研究選用於東台灣篩選出具有耐中高溫(40-50℃)、耐高鹼度(pH 9.5)等特性可較具優勢的直接利用於工業煙道所排放之二氧化碳行固碳作用且含高碳水化合物含量（可高達60%）有利於生產生質酒精。此溫泉藻命名為Thermosynechococcus sp.，其與Nannochloropsis oculata做一比較，以探討不同藻類應用生產生質能源與其能源消耗及溫室氣體等環境友善度。

Application of microalgae cultivation for carbon dioxide (CO2) fixation and bio-fuel production attracts attentions and great expectations as one of the countermeasures to climate change. This is due to the fact that microalgae are the most productive bio-resources considering unit area of land. By utilizing selected productive microalgae and CO2 emitted from an industrial process (ex. power plants), microalgae can be cultivated intensively and provide raw materials for bio-fuel, such as bio-diesel and bio-ethanol. However, additional environmental loads in cultivation (i.e. land area for accepting solar irradiation, consumption of energy, nutrients and water) and conversion to the bio-fuel (i.e. drying, chemical process duties) should be accounted for in highlighting the true potential of this technology. Taking into account of CO2 emission rate from industrial process and other local conditions, choice of microalgal species, cultivation method and its application should be made from a life-cycle point of view.
The objective of this study is to evaluate greenhouse gas (GHG) emission reduction potential of this emerging technology using life cycle assessment. Numerous variations in processes, conditions and species are found around this technology: therefore, in this study, a model for evaluation is established. Using the model, various combinations of process and species alternatives become possible by using the case study provided in this thesis as a template. Consumption of chemicals and energy, GHG emission, GHG emission reduction potential is evaluated for individual combination of processes and microalgal species.
As a first hypothetical case study, application of Nannochloropsis oculata, the lipid-rich (about 50.4% of lipid content) microalgae for an imaginary industrial process is evaluated using the model. After cultivation in a raceway pond, the extracted lipid is used for bio-diesel production via alkali-catalyzed process. In addition to bio-diesel, there is carbohydrate (about 55%) in microalgal residue, which can be utilized as a substrate for bio-ethanol production via saccharification and fermentation. The technologies (ex. chemicals and energy consumption, and GHG emission) for producing bio-ethanol from microalgal carbohydrate (polysaccharide) are missing so far. To estimate the missing data for ethanol fermentation, sugarcane molasses- and switchgrass (cellulose)-derived bio-ethanol are used as maximum and minimum bounds. Assumption behind is that the efficiency of technique for production of microalgae-derived bio-ethanol could be considered as somewhere between that of molasses- (i.e. sucrose) and cellulose- (long polymer of glucose) derived ethanol. In addition to simulating the inventories of microalgae-derived bio-fuel production process, opportunities in enhancement of GHG emission reduction potential is highlighted. Namely, a shift from lipid extraction using conventional squeezing into solvent extraction is evaluated.
Next, comparison of different microalgae-derived bio-fuel production process is made using the model. In this study, the carbohydrate-rich microalgae, Thermosynechococcus sp. is chosen for an alternative to Nannochloropsis oculata. This species is isolated from an alkaline hot spring in eastern Taiwan. The characteristic of Thermosynechococcus sp. has higher tolerance and productivity under high temperature (40~50℃) and high pH conditions. These characteristics could possibly make this species advantageous in carbon fixation from industrial process such as power plant, where utilization of waste heat could be expected. The comparison of the technology provides the researchers of respective technologies with directions of further development and optimization of conditions.

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