連續式臭氧催化系統對2-氯酚去除的動力探討

Abstract

本研究以建立一套連續式臭氧催化系統來處理2-氯酚水溶液，於系統中設置異相觸媒填充塔及金屬離子添加系統，試圖藉由異相觸媒及同相觸媒來探討臭氧對污染物氧化及催化的作用情形。本研究亦以pH值、TOC去除率、水力停留時間、觸媒劑量及溶解臭氧濃度作為影響因子，發展出臭氧異相催化及同相催化的動力方程式，並以此動力模式模擬2-氯酚於臭氧催化過程中污染物礦化的情況。 本研究發現，以沸石為觸媒的異相催化系統對2-氯酚的去除，於酸性條件下（pH=3）可以使TOC去除率由24.48％增加到40.34％，增進效率為67.78％，臭氧消耗率可由14.02降至8.65；而在中性條件下（pH=7）的TOC去除，其增進效率為25.58％；至於鹼性條件下（pH=9）因為水體氫氧自由基的作用以很強，因此異相催化的增進效率僅有4％。在2-氯酚去除的動力模式上，藉由實驗結果可以求得臭氧與污染物直接反應的反應常數（Kapp）為1.08×103 M-1min-1，考慮氫氧自由基與觸媒反應的參與，分別求得反應常數為KB’=2×1010 M-2min-1及Kh’=7.67 M-1min-1g-1L。 以錳離子為觸媒的同相催化系統對2-氯酚的去除，發現酸性條件下（pH=3）TOC的去除效率會與中性條件下（pH=7）相接近，且TOC的去除會隨著觸媒劑量的增加而增加，由以上的結果發現：同相催化系統可以克服臭氧於酸性下所產生的反應瓶頸。在同相催化的模式建立上，我們考慮錳離子僅會與有機酸類產生催化反應，以兩段式的反應型態來描述污染物礦化的過程，求得Kapp,ho=347.06 M-1min-1，KB,ho’=1.0×109 M-2min-1，Kh,ho’=1.41×108 M-2min-1。 在工業廢水的評估上，嘗試以化工廢水、垃圾滲出水及觀音工業區綜合污水處理廠的初沉池廢水作為研究，選擇以錳離子為觸媒的同相催化反應進行半批次實驗，結果發現此系統僅對觀音工業區的廢水可以發揮催化效果，每增加2.5 ppm的錳離子於廢水中將增加約10％的DOC去除率，在臭氧消耗率上可以減少臭氧一半以上的使用量，其節省率約在55.1~64.3％。臭氧同相催化並無法對此三種廢水皆有催化氧化的效應發生，如此的差異推測為廢水污染物濃度、臭氧進流劑量及廢水特性等因素所造成。

The objective of this study is to establish a catalytic ozonation continuous flow system. A catalyst packing bed and an additional apparatus of metal ion were established to treat 2-Chlorophenol aqueous solution and various industrial wastewater. The influence of pH value, TOC removal rate, catalyst dosage, hydraulic retention time and dissolved ozone concentration were considered as operating factors to process the experiment and develop the models of this system. By using these models, simulation of pollutant mineralization was available. The TOC degradation of 2-Chlorophenol aqueous solution by heterogeneous catalytic ozonation with zeolites as catalyst could increase from 24.48% to 40.34% under acid environment. The increasing effect is more than 65%. Furthermore, ozone consumption rate decrease from 14.02 to 8.65 under the same acid environment (pH=3) saving close to 38.3%. While under neutral environment (pH=7), 25.58% increase was observed. As for that under alkaline environment (pH=9), the oxidation of ozone is already strong, thus increase of function is limited, only 4%. Besides, the reaction constant Kapp=1.08×103 M-1min-1 for direct ozonation of pollutant, KB’=2×1010 M-2min-1 and Kh’=7.67 M-1min-1g-1L were calculated while considering the oxidation of OH radical and catalyst. In the homogeneous catalytic ozonation system, the degradation of 2- Chlorophenol aqueous solution with manganese ion as catalyst could reach the similar TOC removal rate under acid environmental (pH=3) comparing with that under neutral environment (pH=7). This result proves that catalytic ozonation with manganese ion could overcome the bottleneck even in acid condition. Morever, Kapp,ho=347.06 M-1 min-1, KB,ho’=1.0×109 M-2min-1 and Kh,ho’=1.41×108 M-2min-1 were found on the basis of the proposed mechanism. Three kinds of wastewater including chemical wastewater, landfill leachate and wastewater from Guan-Yin Industrial Zone were tested for evaluating the function of the homogeneous catalytic ozonation system. More effect was observed for ozonation of wastewater from Guan-Yin Industrial Zone. It could be found that the DOC removal increased with increase of Mn2+ dosage. Furthermore, ozone consumption rate saved close to 55.1~64.3%. It could not be effective for the other wastewater because the different characteristics came from the different kinds of wastewater.