利用生命週期評估探討三種降解水中全氟辛酸之環境友善技術

Abstract

全氟辛酸(Perfluorooctanoic Acid, PFOA)是全氟化合物中最重要的衍生物，因具有環境持久性、生物累積性、長距離傳輸及人類毒性潛勢，被視為一種持久性有機污染物。另外，PFOA具高穩定性的碳-氟鍵結(C-F)，因此不易藉由自然程序破壞，故許多關於降解PFOA的實驗室規模技術陸續被研發出來。但是，這些技術在處理過程中，添加的化學物質、能源使用、廢棄物處理等，皆可能對環境造成直接或間接衝擊，因此必須針對處理過程進行全面的評估。本研究之目的是以生命週期評估法分析三種實驗室規模的降解水中PFOA技術。這三種技術分別為：Case 1 以微波輔助高級氧化法降解水中全氟辛酸(microwave-induced persulfate oxidation, MIPO)、Case 2 以超音波促進光催化氧化法降解水中全氟辛酸(sonication-assisted photo-catalytic oxidation, SAPO)、Case 3 以薄膜外加電場去除水中全氟辛酸(electro-membrane filtration, EMF)。使用生命週期評估軟體SimaPro 7.2 及其內建之資料庫，對三案例材料製備和PFOA降解過程進行盤查分析後，再經 IMPACT 2002+評估模式量化其潛在衝擊。結果顯示，MIPO及SAPO以材料製備階段貢獻為主，而EMF則是降解實驗階段，三案例皆以電力耗用為環境衝擊之主要因素，故對環境之影響衝擊類別主要於非再生能源、氣候變遷、可吸入無機物項目，換算成損害評估結果，則對資源衝擊最大，其次是氣候變遷。以濃度標準功能單位(將PFOA之濃度去除至 30 ppm)來看，環境衝擊程度為Case 2 (SAPO) > Case 3 (EMF) > Case 1 (MIPO)；若由重量功能單位(去除 6.15 mg的PFOA)，結果則是Case 1 (MIPO) > Case 2 (SAPO) > Case 3 (EMF)。由本研究結果可知選用兩種不同功能單位，能源皆為關鍵因子，故如何提高能源效率、減少能源使用是未來需努力的方向。本研究之評估雖為實驗室規模，但最終評估後的結果，仍可供實場處理水中全氟辛酸作為參考，選擇對環境影響最友善的技術，以達到綠色化學的目標，即對環境和健康之最小危害。

Perfluorooctanoic Acid (PFOA) is the most important derivative of the Perfluorinated Compounds (PFCs). It is an unnatural compound that appears in the environment as a result of human production processes. PFOA is used extensively in the manufacturing of fluoropolymers and a wide range of industrial products such as surfactants, fire retardants, as well as oil, stain and grease repellants. The life cycle of all PFOA related products including producing, using, and discarding, incurs the risk of water, air, and soil pollution, with water pollution being the most prevalent. Factors such as environmental persistence, bioaccumulation, long-range environmental transport issues, and potential toxicity to humans contribute to PFOA as being regarded as a one of the Persistent Organic Pollutants (POPs). Furthermore, PFOA is not easily destroyed by natural processes due to its extreme stability resulting from strong C-F bonds. There are currently a variety of methods for degrading PFOA in the water, however, these treatment processes may all cause direct or indirect impacts to the environment through the addition of chemicals, inefficient energy use, improper waste treatment, and so on. As such, a comprehensive assessment to determine appropriate treatment processes is essential. In this study, the main objective is using Life Cycle Assessment (LCA) to compare the environmental impacts of three environmentally friendly processes for the decomposition of PFOA from water. The three kinds of technologies are: (1) microwave-induced persulfate, MIPO; (2) sonication-assisted photo-catalytic oxidation, SAPO; and (3) electro-membrane filtration, EMF. Environmental assessments are carried out using SimaPro 7.2 LCA software and utilizing the IMPACT 2002+ methodology to evaluate the potential environmental impact. The results revealed the major causes of environmental impact for Case 1 (MIPO) and Case 2 (SAPO) are both materials preparation, and for Case 3 (EMF) is appling external magnetic field during electro-membrane treatment. The top three environmental impact categories for all three cases are non-renewable energy, global warming, and respiratory inorganics. While choose the functional unit of concentration standard (the concentration of PFOA removed to 30 ppm), the degree of environmental impact is Case 2 (SAPO) > Case 3 (EMF) > Case 1 (MIPO); and under the functional unit of weight (removal of 6.15 mg PFOA), the degree of environmental impact is Case 1 (MIPO) > Case 2 (SAPO) > Case 3 (EMF). Under two different functional units, the key factors are both energy consumption, so improving energy efficiency and reducing energy use are goals to reach in the future. The assessment of these laboratory-scale treatments for degrading PFOA from water will be valuable for real work sites. This may assist in identifying the most environmentally friendly technologies for achieving green chemistry goals, namely the minimization of environmental and health hazards.