在淨水及廢水處理單元中，薄膜技術一直是被廣泛利用的技術之一。然而，薄膜在淨水處理上最大的缺點為阻塞。常見的薄膜清理技術為液體反洗或化學藥劑清洗；但液體反沖洗效果有限，使用化學藥劑亦會衍生出一些化學廢棄物問題。有鑑於此，本研究乃結合薄膜前混凝與超音波清洗來減少化學洗膜藥劑的使用，達到延長薄膜壽命的目的。
本研究係探討過膜前不同預混凝處理並結合超音波清洗薄膜之技術，對PTFE(polytetrafluoroethylene)材質之微過濾薄膜（micro-filtration, MF）過濾行為之影響。首先探討人工原水於薄膜過濾前利用硫酸鋁以及氯化鐵兩種不同混凝劑並在不同混凝機制下進行混凝前處理，觀察膠羽特性，以研判薄膜於不同膠羽特性下之通量。接下來針對超音波清洗薄膜結垢進行評估，針對不同特性膠羽於薄膜上之積垢進行超音波清洗，清洗後觀察薄膜通量回復率，探討前混凝程序中的膠羽特性與過濾時比阻抗對超音波清洗薄膜後通量回復率的影響。
研究結果顯示，預先混凝經MF過濾配合超音波處理後通量有明顯提升，可以降低薄膜阻塞程度及降低總阻抗。此外，過膜通量與通量回復率隨著膠羽特性與阻塞機制不同而異，硫酸鋁與氯化鐵於不同混凝機制對通量提升順序為電性補丁(EPE)>電性中和(CN)>沉澱網除(SW)；對於阻塞機制EPE以孔洞阻塞為主、CN以孔洞阻塞和濾餅阻塞為主、SW以濾餅阻塞為主；通量回復性則是SW>CN>EPE，但整體而言硫酸鋁的通量回復性優於氯化鐵。由結果可知，預混凝形成之膠羽會影響薄膜上濾餅的特性，且進一步的影響到過膜通量、阻塞機制及通量回復性。 Membrane process is one of the technologies utilized extensively in the water purification and wastewater treatment processes. However, one of the main barriers for greater use of membrane process is membrane fouling. Nowadays several methods are available to reduce membrane fouling. Including backwashing and chemical membrane cleaning. Unfortunately, backwashing is limited to removing strongly adherent films, and chemical cleaning of membranes is expensive. Ultrasonic provide an alternative technology for membrane fouling control.
Therefore, the purpose of this research is to investigate the control of membrane fouling in the presence of clay-coagulant combined with ultrasonic. Polytetrafluoroethylene(PTFE) was used as micro-filter. The parameters of this study are coagulant types (aluminium sulfate and ferric chloride) and coagulant mechanism. Pre-coagulation was initially performed using clay mixed either with aluminium sulfate or ferric chloride under different coagulation mechanisms. The effect on the characteristic of the flocs was observed under different coagulant mechanisms. The aim is to assess and examine the effectiveness of ultrasonic membrane cleaning based on the floc characteristic and total resistance after filtration in the pre-coagulation process.
The results demonstrated that a lower flux was observed after membrane filtration in all conditions. The use of ultrasonic increased and improved the flux of the used membrane, and further reduced the block condition of membrane and the total resistance. Furthermore, the flux and recovery rate were influenced by floc characteristic and block mechanism. Aluminium sulfate or ferric chloride under different coagulant mechanism using either coagulation affected the advancement flux order in the following sequence: electronstatic patch effect (EPE)>charge neutralization(CN)>sweep flocculation(SW). The primary block mechanism of coagulant mechanisms were different as following: pore blocking for EPE, pore blocking and cake blocking for CN, and cake blocking for SW. The flux recovery rate was SW>CN>EPE, and the flux recovery rate of aluminium sulfate was better than ferric chloride. The results indicate pre-coagulation floc can affect the characteristic of the cake deposited on the membrane, and further influence the flux across the membrane, the block mechanism and flux recovery rate.
