利用 Fenton 處理法降解水中加保扶之研究

Abstract

加保扶 (carbofuran) 為一種普遍且被廣泛使用的殺蟲劑，主要用途為殺死土壤中昆蟲及害蟲，其使用量約占每年台灣總殺蟲劑使用量 (15,478 噸) 的百分之七，由於加保扶具有高致毒性與高水溶解性 (25oC, 700 mg/L)，因此加保扶的存在與處理問題必須重視。利用 Fenton 法處理廢水中的毒性有機污染物為一高效率且省時、常見的方法，本研究即利用 Fenton 法具備之特性，處理水中不同濃度之加保扶 (10 mg/L 與 50 mg/L)；由於文獻指出 pH 值為 3 的條件下，Fenton 試劑對於有機物的降解效果為最佳，因此本研究透過中央合成設計搭配反應曲面法，進行實驗組數之規劃與結果分析，於固定初始 pH 值為 3 的條件下，分別探討初始加保扶濃度為 10 mg/L 與 50 mg/L 時，亞鐵離子 (0-10 mg/L) 和過氧化氫 (0-200 mg/L) 濃度對於加保扶降解率之影響，目的為決定其最佳化之操作條件。除此之外，本研究亦選擇加保扶降解效率最佳之實驗組，利用 GC-MS 分析其可能之中間產物，並推導其降解過程之反應途徑 (pathway)。

研究結果顯示，加保扶的降解率隨著亞鐵離子和過氧化氫濃度的增加而提升，當添加的亞鐵離子和過氧化氫濃度分別在 5 mg/L 和 100 mg/L 以上時，90% 以上的加保扶可在 5 分鐘內被有效降解。相反地，當水中並無添加過氧化氫或是亞鐵離子的條件下，此時加保扶則無任何被降解的現象。當加保扶的初始濃度為 10 mg/L 時，其最佳的 Fenton 試劑加藥量分別為亞鐵離子 7.4 mg/L 與過氧化氫 143 mg/L，最佳降解率與最佳 Fenton 試劑添加量之關係可由 (方程式) 計算而得。根據 GC-MS 分析結果可知 7-benzofuranol,2,3,-dihydro-2,2-dimethyl (分子量 164)、7-hydroxy-2,2-dimethyl-benzofuran-3-one (分子量178) 與 1,4-Benzene-di- carboxaldehyde (分子量 134) 為加保扶被 Fenton 試劑降解之主要中間產物，根據中間產物分析之結果即可推導並獲得加保扶之反應降解途徑。

Carbofuran (C12H15NO3) is a broad spectrum, carbamates insecticide widely used to control certain soil-borne insects and nematodes. In Taiwan, carbofuran accounts for about 7% of the 15478 tons of insecticides produced per year. Carbofuran usage has received intensive concern not only due to its heavy use but also due to its high oral toxicity. The wastewater treatment processes using the Fenton reaction are known to be very effective in the removal of many hazardous organic pollutants from water. In this study, Fenton process was applied to remove carbofuran from aqueous system. Fenton experiments were conducted in batch mode at two different carbofuran concentrations i.e. 10 and 50 mg/L and at fixed initial pH of the system i.e. pH 3. Batch experiments at each carbofuran concentrations were designed by central composite design (CCD) with two independent variables i.e. Fe2+ and H2O2. The efficiency of the experiments was determined based on the percentage removal of carbofuran. Finally, a statistical experimental design and the response surface methodology were used to optimize the Fe2+ and H2O2 concentrations for maximum percentage removal of carbofuran.

More than 90% of carbofuran removal was observed within 5 min of Fenton reaction with Fe2+ concentration above 5 mg/L and H2O2 concentration above 100 mg/L. The increase in Fe2+ and/or H2O2 concentrations beyond 5 and 100 mg/L, respectively, produced 100% carbofuran removal in the Fenton process. No carbofuran removal was observed when either Fe2+ or H2O2 was absent in the system. Based on the experimental observations, the optimal Fe2+ and H2O2 dosages required for 10 mg/L of aqueous carbofuran removal were estimated as 7.4 and 143 mg/L, respectively. Carbofuran degradation experiments were repeated at optimal Fe2+ and H2O2 concentrations and the samples were collected at various time intervals. The collected samples were analyzed in gas chromatography-mass spectrometry (GC-MS) for the determination of carbofuran degradation pathway. The GC-MS analysis indicated that carbofuran was oxidized to 7-benzofuranol,2,3,-dihydro-2,2-dimethyl (m/z 164), 7-hydroxy-2,2-dimethyl-benzofuran-3-one (m/z 178) and 1,4-Benzene-di- carboxaldehyde (m/z 134).