利用過硫酸鹽在室溫下氧化全氟辛酸之研究

Abstract

本研究為利用過硫酸鹽將全氟辛酸(Perfluorooctanoic acid, PFOA)於室溫水溶液中降解，實驗操作在不同溫度下(20、30、40℃)、改變初始氧化劑過硫酸鹽濃度、改變初始水溶液酸鹼值，針對這些條件作全氟辛酸的降解探討。實驗結果顯示，在酸性情況下、過硫酸鹽的濃度為200 mM時的氧化速率最快，20、30、40℃其反應的半衰期分別為330、61.33、13.46個小時，溫度越高反應速率越快；但此實驗也證實在室溫的情況下過硫酸鹽對全氟辛酸還是有其氧化效力存在，在20℃反應時間達865個小時全氟辛酸還剩下14.5 %。在氧化劑過硫酸鹽的使用上，對於相同污染物濃度其消耗量大致相同，與溫度、時間無關；過硫酸鹽在整個反應過程中，除在40℃的使用量為32.9 %，其餘兩者的使用量都小於10 %，顯示過硫酸鹽在常溫未催化下的反應性的確很低。此實驗主要作用的氧化劑為過硫酸鹽溶於水後經熱活化或酸催化產生的硫酸根自由基SO4-•，過硫酸根離子本身也是很重要的氧化劑之一。所有實驗數據符合假一階方程式，反應速率常數分別為0.0515、0.0113、0.0021 h-1。此實驗方法操作成本低、設備所需簡單，具有其實際應用性。

In this research, a treatment to decompose the persistant and bioaccumulative perfluorooctanoic acid (PFOA) in water with high concentration of persulfate (S2O82-) at ambient temperature was developed. Persulfate is an effective oxidant for PFOA degradation without using any activated technology, even at a room temperature. The objectives of this study were to investigate the influences of pH ( pH 2.5, 7, and 11) and the persulfate doses (50-200 mM) on decomposition of PFOA at 20, 30 and 40 °C. Half-lives of PFOA degradation at 20, 30, and 40 °C. were 330, 61.3, and 13.46 h, respectively. Based on the laboratory experiment results, PFOA is completely decomposed by persulfate to form shorter-chain of perfluorinated carboxylic acids (PFCAs) and fluoride ions, with defluorination efficiency reaching 97 % within 218 hours at 40 °C. When the reaction temperature is maintained at 20 °C, 65 % of PFOA is decomposed with 41 % defluorination efficiency after 865 hours of reaction. Experimental data can be well simulated with pseudo first-order kinetics as the PFOA degradation, and the rate constants are 0.002 h-1 at 20 °C, 0.011 h-1 at 30 °C, 0.052 h-1 at 40 °C. The solution temperature has a definite impact on the decomposition of PFOA by persulfate. Increasing system temperature resulted in a greater increase in PFOA degradation rates than lowering system temperature.