以超聲波程序提升電混凝效能之研究

Abstract

電混凝在廢水的使用上已有很長時間，可應用於去除染料、重金屬等物質，特別是針對有機物及懸浮固體，可用於潔淨、無色、無臭味之水質，其優點可避免化學品的使用、設備簡單、操作容易且污泥量少；然而，使用一段時間後，極版表面會發生鈍化現象生成惰性層，惰性層會增加阻抗以及減少混凝物質的產生。據此，本研究主要以合成水樣評估超聲波結合電混凝程序對於極版之惰性層控制去除以及探討陰離子對於惰性層所造成之影響。 本研究以染料Reactive Blue 19(RB19)、磷酸鹽及硝酸鹽為研究對象，分別探討超聲波所造成之影響，RB19之研究結果發現，為添加超聲波程序時，極版上之惰性層亦會產生些微之上升，添加超聲波程序後可使表面阻抗下降，並可使溶液中粒子粒徑變小，因此可以增加更多的面積，有利於染料之去除，釋出的鋁離子本身則帶正電，有利於與帶負電之染料吸附結合後沉澱去除，而超聲波在使用過程中會造成水中形成膠羽被打破，此現象則可透過雙槽反應器以及間歇式超聲波程序避免，以間歇式超聲波程序複合電混凝程序可提升去除效率約10%，並可避免在超聲波使用過程中造成大量的能源消耗。動力學結果發現，其結果較符合擬一階之方程式。 以陰離子磷酸根為目標污染物，結果發現，濃度越高之磷酸根，極版表面所產生之惰性層則越高，使得釋鋁量下降並降低去除效率，對於陰離子所造成之惰性層則可有效的透過超聲波程序以及添加氯離子去除表面之惰性層。氯離子可溶解惰性層，Al2O3與氯反應形成Al(OH)2Cl、Al(OH)Cl2、AlCl3。超聲波則可產生空洞現象，使微泡累積至固液體表面之間，爆裂後產生瞬間高溫高壓去除惰性層，在超聲波添加的瓦數以150 W以下具有最佳效果，而兩者同時添加並無協同效應，使用任一方法均可將表面之惰性層去除，使釋出之鋁離子不受到惰性層之影響，效率提升可超過50%。在多次重複實驗就中發現，添加超聲波之電混凝程序後可有效增加磷酸鹽之去除率並且延長極版的壽命。最後，在多陰離子實驗中發現，超聲波可有效提升含有磷酸根及碳酸根溶液之去除效率。

Electrocoagulation (EC) has a long history of use in as a wastewater treatment process. It has been applied to remove dye, and heavy metal, especially in organic and suspended matter. Deploying EC process to produce clear, colorless and odorless water exhibits many advantages, such as avoidance of chemicals use, simplicity in configuration, ease of operation, and low sludge generation. However, electrode passivation occurs on the surface of electrode after a period of operation. The passive film increases the resistance and diminishes the release of the coagulation material. The removal efficiency is decreased. The aim of this study was to evaluate the effects of integrating the methods on eliminating the passive film on the electrode surface to enhance energy efficiency and the contamination removal efficiency from synthesized water during ultrasound-electrocoagulation (sono-EC). The result shows the passive film is increased slightly by using the dye of Reactive Blue 19 as contamination. Integration of ultrasound and EC process are deceased the impedance on the electrode surface. Moreover, Ultrasonic treatment can reduce the size of particle, thereby increasing their surface areas and promoting their sorption capacity. The releasing of aluminum ion is positive charge; it is favor to adsorb the dye with negative charge. However, the ultrasonic process is broken the floc in the operation periods, it is avoided by double reactor or intermittent process. The ultrasound of intermittent process is not only prevented the floc broken, but also consumption unnecessary energy. The EC process can be best described using variable-order kinetics. The result shows the passive film is proportion to the concentration by using phosphate as contamination. It is also effected the amount of releasing aluminum particle, moreover it is decreased the removal efficiency. From the result, addition of chloride or integration of ultrasound are both efficiency to reduce the passive film. The chloride can be dissolve the passive film, the Al2O3 is active with chloride, the compound is formed Al(OH)2Cl, Al(OH)Cl2 and AlCl3. The ultrasound induces cativation. Bubbles grow in successive cycles forming bubbles of cavitation which, at sufficient high power, reach an unstable size and collapse violently. It is called ‘‘hotspots’’ with high temperature and pressure. The optimal ultrasonic power to treat contamination is under 150 W. However, the chloride and ultrasound additions do not exhibit synergistic effects. Because the passive film is limited, it is reduced by one of way. Cycling runs testing shows ultrasound can be used with EC to enhance the phosphate removal efficiency and extend the life of an electrode. The muti-anion experiment shows, ultrasound is useful to enhance the removal efficiency with phosphate and carbonate anion in the solution.