以犧牲陽極加藥浮除全氟辛酸之研究

Abstract

全氟辛酸(PFOA)為一工業合成之介面活性劑，常被廣泛地應用當作抗油抗水的塗料。PFOA在自然環境中十分穩定，不易被降解，同時具有生物累積性與生物毒性，在國際間已引起高度的關注與管制，目前已有許多研究關於PFOA的去除與降解，如超聲波、光降解、過硫酸鹽催化、過濾與吸附等等。其中，電化學與浮除法是反應時間較短、且效果顯著的方法。 本研究透過電混凝反應中的犧牲陽極釋出金屬離子，結合混凝與曝氣浮除快速將汙染物去除，並在過程中探討pH值的變化。研究顯示，在鐵、鋁、鋅三者金屬中，鋅的處理效果最佳，隨電流密度上升，反應速度也會增加，由於鋅金屬形成之氫氧化物具有良好的架橋吸附效果，因此能顯著去除溶液中的PFOA，在電流密度37.5 mA/cm2 下，鋅金屬電極可在2分鐘內達到98 %的PFOA去除效果；電流密度為6.25 mA/cm2 時，反應也在12分鐘達到97 %的去除效果。 在pH值對浮除效果的影響的實驗中，測試不同pH的條件下，添加Al金屬進行曝氣。結果顯示，Al金屬在pH=5時因生成帶大量正電的Al13物質，與帶負電之PFOA形成穩定的氣泡被曝氣至表面，曝氣5分鐘後可達98%的去除率。 電混凝浮除法中，電解質濃度由2 mM提高至20 mM，可些微提高去除率，但操作電壓由20 V下降至2.5 V，可有效降低能耗；此外，反應會受陰離子種類的影響，溶液中若存在負電性越高之陰離子，會使去除效果明顯降低。 反應產生之膠羽透過傅利葉轉換紅外線光譜儀(Fourier-transform infrared spectroscopy, FTIR)分析，於穿透光譜的結果中可發現C-F2與C-F3之特徵峰值出現，說明PFOA被吸附於膠羽中，以達去除效果。證實透過犧牲陽極產出之金屬離子能有效去除水中PFOA。

Perfluorooctanoic acid (PFOA) is an industrial synthetic surfactant which is widely used as an oil and water resistant coating. PFOA is very stable in the natural environment, which means it cannot be degraded easily. Meanwhile, a lot of countries have paid high attention to PFOA due to its bioaccumulation and biological toxicity. There have been many studies on the removal and degradation of PFOA, such as ultrasound, photolysis, persulfate catalysis, filtration and adsorption, and so on. The method combined with electrochemistry and floatation is effective and efficient way to remove PFOA in water. In this study, the metal ions were released by the sacrificial anode in the electrocoagulation reaction. By using electrocoagulation and floatation simultaneously, contaminants could be removed rapidly. Also, the pH value was discussed in the process. Studies have shown that among the metals of iron, aluminum and zinc, zinc has the best efficiency. As the current density increased, the reaction rate accelerated at same time. Since the hydroxide formed by zinc metal had an excellent performance on bridging adsorption , At a current density of 37.5 mA/cm2, the zinc metal electrode achieved 98% removal rate of PFOA in 2 minutes. At a current density of 6.25 mA/cm2, the reaction could reach 97 % removal rate in 12 minutes respectively. In the experiment of the effect of pH on the floating, aluminum ions were added for aeration under conditions of different pH values. The results showed that the Al metal formed Al13 substance at pH=5, which had a large amount of positive charges. Al13 formed a stable bubble with the negatively charged contaminant such as PFOA, then aerated to the surface, reaching about 98 % removal rate after 5 minutes of aeration. Moreover, raising the electrolyte concentration could both increase the removal efficiency and lower the power demand. In addition, the reaction was affected by the type of anions. The presence of an anion with higher negative charges resulted in a significant reduction in the removal rate. The flocs produced by the reaction were analyzed by Fourier-transform infrared spectroscopy (FTIR). The peaks of C-F2 and C-F3 were found in the results of the spectra, indicating that PFOA was adsorbed in the flocs. It was confirmed that the metal ions produced by the sacrificial anode can effectively remove the PFOA in the water.