以電混凝浮除法去除全氟辛酸之研究

Abstract

全氟辛酸(Perfluorooctanoic acid, PFOA)被廣泛運用於工業和商業活動上，由於其化學穩定性和生物累積性，全氟辛酸會對自然環境和人體健康產生嚴重的危害，雖然「斯德哥爾摩公約」已限制了全氟辛酸的使用，但是半導體製程、紡織塗層等少部分特殊用途受到豁免，在這些製程中仍能使用全氟辛酸，因此全氟辛酸的使用及處理仍受到全球的關注。本研究針對全氟辛酸，利用浮除法(flotation)、電混凝(electrocoagulation, EC)以及電混凝浮除(electrocoagulation-flotation, ECF)三種方法來去除水中的全氟辛酸，並添加界面活性劑和氯化鋅作為捕集劑，以增進全氟辛酸的去除效果。研究結果顯示，在各種界面活性劑中，陽離子界面活性劑對全氟辛酸去除效果遠高於陰離子界面活性劑，而與全氟辛酸具有相似結構的界面活性劑作為捕集劑能有較好的去除效果，使用與全氟辛酸碳鍊長度相同的正辛基三甲基溴化銨(octadecyl trimethyl ammonium bromide, OTAB)作為捕集劑進行泡沫浮除可以在20分鐘內完全去除全氟辛酸。在電混凝的過程中添加氯化鋅可以增進絮凝效果，這種效果增強了浮選效果，可以在20分鐘內將全氟辛酸去除率由75%左右提升至將近100%。在電混凝系統中添加界面活性劑可以增進系統的浮除效果，使其變為電混凝浮除，使用癸基三甲基溴化銨(dodecyltrimethylammonium bromide, DTAB)可以在10分鐘內去除95%以上的全氟辛酸。將上浮的泡沫冷凍乾燥後進行特徵分析，包括X光繞射儀(XRD)、掃描電子顯微鏡(SEM)、傅立葉紅外光譜儀(FTIR)以及X射線光電子能譜儀(XPS)，結果顯示全氟辛酸確實隨著泡沫被去除，並確認去除機制除了全氟辛酸梭酸基團與鋁膠羽鍵結以及全氟辛酸與鋁膠羽的靜電吸附之外，全氟辛酸與鋁膠羽的氟-鋁配位鍵結也是主要去除機制之一。研究最後探討各方法之能量效率，添加DTAB的ECF其能量效率遠優於他文獻的方法，能效(G50)是其他文獻方法的100倍，而能耗(EEO)是其他文獻方法的1/100。ECF能在很短的時間內自水中去除全氟辛酸，能耗也優於其他方法，是具有商業化潛力的全氟化合物去除方法。

Perfluorooctanoic acid (PFOA) is widely used in industrial and commercial activities. Due to its chemical stability and bioaccumulation, PFOA can cause serious harm to the natural environment and human health. Although the 'Stockholm Convention' has restricted the use of PFOA, a small number of particular uses, such as semiconductor process, and textile coating, are exempted, and PFOA can still be used, so the use and treatment of PFOA still attract global attention. This study removed PFOA by three methods: flotation, electrocoagulation (EC), and electrocoagulation-flotation (ECF). Surfactant and zinc chloride were added as collectors. Aggregate to enhance the removal of PFOA. The results show that among various surfactants, the removal effect of cationic surfactants is much higher than that of anionic surfactants, and surfactants with similar structures to PFOA can have better removal effects as collectors. PFOA can be removed entirely within 20 minutes by froth flotation using octadecyl trimethyl ammonium bromide (OTAB) as a collector, with the same carbon chain length as PFOA. The addition of zinc chloride in electrocoagulation can enhance the flocculation effect, which enhances the flotation effect and can increase the removal effect of PFOA from about 75% to nearly 100% within 20 minutes. Adding surfactants to the electrocoagulation system can enhance the flotation effect of the system, making the system into an electrocoagulation-flotation, and the use of dodecyl trimethyl ammonium bromide (DTAB) can remove more than 95% of PFOA in 10 minutes. The floating foam was freeze-dried and then analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), fourier transforms infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results confirmed that PFOA was removed with foam. And the primary removal mechanisms are bonding of monomeric cationic species to anionic sites of the organic molecules, bonding of polymeric cationic species, adsorption on the flocs, which are superficially positively charged, coordination of covalent bonds between fluorine and aluminum, co-flotation with surfactant, and forming micelle with surfactant. The energy efficiency of each method is discussed at the end of the study. The energy efficiency of ECF with DTAB is much better than that of other literature methods. The energy efficiency (G50) is 100 times than other literature methods, and the energy consumption (EEO) is 1/100. ECF can remove PFOA from water in a very short time, and the energy consumption is also better than other methods. It is a method for removing PFOA with commercial potential.