氧化鐵覆膜活性碳催化氧化及吸附苯甲酸之研究

Abstract

工業界所採用的傳統Fenton處理方法，一般多應用於有機性廢水的處理，由於其反應快且操作簡易，因此廣為業界所採用，但傳統Fenton法會產生大量污泥，污泥的處置與處理亦是一大問題。 本研究使用兩種不同材質的活性碳(A，B)為擔體，並比較以這兩種活性碳為擔體之FeOOH/GAC (氧化鐵覆膜活性碳) 對苯甲酸(BA)的去除效率。研究初期，填入兩種不同的活性碳於流體化床反應槽中，持續進流FeSO4、H2O2、BA，長晶4、6、8週，以探討FeOOH/GAC對苯甲酸之吸附、催化及氧化特性的變化。長晶後的觸媒顆粒都會取出做批次氧化及吸附實驗，以得對苯甲酸的去除效率及吸附等溫線，選出較適合作為擔體之活性碳。 比較兩種原始活性碳的特性發現，A之BET比表面積較B高，且我們以H2O2氧化原始活性碳，反應六個小時之後測其所釋出之TOC濃度，發現A所消耗的H2O2為B之兩倍但釋出的TOC濃度卻只有B的一半，由此得知A的性質較B穩定。養晶四週及六週時，FeOOH/GACA之總鐵量(≣Fet)、BET表面積及對苯甲酸的去除效率均較FeOOH/GACB高，且隨長晶時間增加，兩種FeOOH/GAC的總鐵量(≣Fet)增加、BET表面積減少、活性碳的吸附能力下降。初期結果顯示A對苯甲酸的處理較佳，所以在後續八週的研究中針對A活性碳做更深入的探討，FeOOH/GACA之異相催化氧化反應，四、六、八週之擬一階反應速率常數k值分別為0.025、0.0422、0.0403 hr-1，結果顯示四週到六週時，氧化能力隨FeOOH/GAC上的總鐵含量增加而上升，但當總鐵含量增加到一上限時，氧化能力已趨於穩定﹔同相及異相共存之氧化反應八週效果最好，其次是六週。

Conventional Fenton process is generally applied for organic wastewaters treatment. This method has received great industrial attention because it is fast and easy to operate. This study intends to improve the fluidized-bed Fenton reactor for advanced wastewater treatment process. Two granular activated carbon-supported FeOOH systems, A- and B shell-based, replace the granular brick support and their performances are compared. The crystals are allowed to grow on the surfaces of the granular activated carbon (GAC) for 4, 6, and 8 weeks while benzoic acid (BA), H2O2 and FeSO4 are continuously fed into the column. The adsorption characteristics of BA on and the catalytic oxidation of the FeOOH/GAC system are monitored. The GAC-supported FeOOH crystals are isolated from the reactor and used in the batch BA adsorption and oxidation experiments. Before the coating of FeOOH onto the GAC surface, the specific surface area of the A-based GAC (GACA) is higher than that of the B-based GAC (GACB), while the GACB is more susceptible to oxidation. After four to six weeks’ incubation, the specific surface area, and BA removal of the FeOOH/GACA are higher than those of FeOOH/GACB. The total iron contents of the two FeOOH/GAC increase whereas the specific surface area and the adsorption decrease with the incubation time. Since the GACA system has a better removal of BA, the rest of the study concentrates on this system. The variation in reaction rate constants of the heterogenous catalytic oxidation of FeOOH/GACA indicates that the oxidation ability increases with the total iron content increase in the first four to six weeks of incubation. From six to eight weeks, the oxidation ability gradually stabilized while the total iron content keeps increasing. In the system involving both heterogenous and homogenous oxidation, the BA removal efficiency of 8-week FeOOH/GACA is better than the 6-week FeOOH/GACA does.