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研究生： 侯若亭
Utami, Woro Nastiti
論文名稱： 抑垢劑對控制碳酸鈣於RO薄膜阻塞之研究
The Use of Antiscalant on Calcium Carbonate Scaling Control for RO Filtration
指導教授： 葉宣顯
Yeh, Hsuan-Hsien
學位類別： 碩士
Master
系所名稱： 工學院 - 環境工程學系
Department of Environmental Engineering
論文出版年： 2012
畢業學年度： 100
語文別： 英文
論文頁數： 111
外文關鍵詞： calcium carbonate, antiscalant, reverse osmosis, scaling morphology
相關次數： 點閱：98  下載：4 
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    • Calcium carbonate has emerged as main foulant of scaling in reverse osmosis (RO) filtration which leads to higher operation maintenance cost and reduced performance of RO filtration. A study of CaCO3 scaling morphology, which covered several factors including feed water quality, antiscalant type, and antiscalant dose, was carried out in static jar test and dynamic reverse osmosis filtration. In static jar test, Flocon 190 (organic phosphonate) and MSI 310 (polymer antiscalant) can maintain dissolved calcium about 90% of its initial value in solution with low initial saturation index. However, MSI 310 showed less effectiveness than Flocon 190 in higher initial saturation index solution in maintaining dissolved calcium.

    In RO filtration using artificial solution as the feed water, high dose (60 mg/l) of both Flocon 190 and MSI 310 resulted in severe flux decline (about 75%) which was caused by formation of dense cake layer covering over RO membrane surface. Permeate flux of solution with 60 mg/l antiscalant declined rapidly in first 50 minutes and got stable until the end of filtration, while antiscalant – free solution showed gradual and continuous flux decline. Formation of dense cake layer by nanometer particles (size about 50 nm) blocked RO surface in short times. Consequently, already blocked RO membrane surface led to a low and stable permeate flux until the end of filtration. In antiscalant-free solution, calcium carbonate crystals tended to coherent with one another and got denser over the time, which was responsible for gradual and continuous flux decrease.

    For each antiscalant, there exists an optimum dose for preventing flux decline in artificial solution filtration. Surface analysis of fouled membrane showed that addition of low dose antiscalant reduced calcium carbonate crystals size (size ≤ 1µm) and altered calcium carbonate crystals morphology. Deposits of deformed calcium carbonate crystals were looser and less compact than that in antiscalant free solution, and resulting in higher permeability. From SEM result, it was speculated that antiscalant adsorbed in active site of nucleating calcium carbonate crystal and halted crystal growth. The changes of crystal size and morphology were caused by preferential growth of crystal faces with lower surface coverage by antiscalant molecule.

    In tap water filtration, two kinds of deposit were found. The first kind was complex scaling of aluminum, silica, and calcium as three main elements which was observed by SEM - EDX analysis. This complex scaling formed a rough cake layer onto RO surface. The second kind was rhombohedral calcite crystals which tended to agglomerate into bigger particle (size: 3-5µm). Addition of Flocon 190 and MSI 310 could reduce amount of crystals and prevent recrystallization of CaCO3 into stable phase, but failed to prevent complex scaling under various dosage.

    Flocon 190 showed a better performance than MSI 310 in preventing flux decline, caused by calcium carbonate crystallization both in artificial solution and tap water. Presence of antiscalant during calcium carbonate precipitation could change particle size and morphology and affect deposit morphology onto RO membrane surface. Maintenance of proper antiscalant dosing is essential in RO filtration since different dose antiscalant could lead to different morphology and size of calcium carbonate crystals.

    ABSTRACT i ACKNOWLEDGMENT iii TABLE OF CONTENTS v FIGURE INDEX viii TABLE INDEX xii CHAPTER 1 INTRODUCTION 1 CHAPTER 2 LITERATURE REVIEW 4 2.1 Calcium Carbonate Crystallization 4 2.1.1 Solution Equilibria 4 2.1.2 Calcium Carbonate Polymorphs 5 2.1.3 Calcium Carbonate Crystallization Mechanism 9 2.2 Membrane Application 12 2.2.1 Reverse Osmosis 15 2.2.1.1 Reverse Osmosis Membrane Material 16 2.2.1.2 Spiral Wound Reverse Osmosis Membrane 18 2.2.1.3 Reverse Osmosis Flow 18 2.2.1.4 Key Factors Affecting Reverse Osmosis Performance 20 2.2.2 Scaling and Fouling of Reverse Osmosis 21 2.2.3 Application of Antiscalant on CaCO3 Precipitation 28 2.2.4 Prediction of Scaling Tendency 29 2.2.5 Surface Analysis and Water Quality Analysis 31 2.2.5.1 Scanning Electron Microscopy 31 2.2.5.2 Inductively Coupled Plasma – Atomic Emission Spectrometry 31 2.2.6 Analytical Methods for Aggregation of CaCO3 32 2.2.6.1 Refiltration Test 32 2.2.6.2 Particle Counting 33 CHAPTER 3 MATERIAL AND METHODOLOGY 35 3.1 Solution Preparation 37 3.2 Jar Test Precipitation Experiment 40 3.3 Reverse Osmosis Experiment 41 3.4 Water Quality Analysis 45 3.5 Surface Analysis 48 CHAPTER 4 RESULTS AND DISCUSSION 49 4.1 Static Jar Test Experiment 49 4.1.1 Dissolved Calcium of Jar Test 50 4.1.2 SEM Result of Static Test 53 4.2 Dynamic Test Reverse Osmosis Filtration 57 4.2.1 Artificial water (SI: 2.35); Filtration time 4 h 58 4.2.1.1 Flux Behavior 58 4.2.1.2 SEM Analysis 60 4.2.2 Artificial Water (SI: 2.35); Filtration time 10 h; low dose antiscalant 66 4.2.2.1 Flux Behavior 66 4.2.2.2 SEM Analysis 69 4.2.3 Refiltration and Particle Counter 75 4.2.4 Tap Water; Filtration time 10 h 81 4.2.4.1 Flux Behavior 81 4.2.4.2 SEM Analysis 85 CHAPTER 5 CONCLUSIONS & SUGGESTION 96 5.1 Conclusions 96 5.2 Suggestion 98 REFERENCES 99 APPENDIX A CALCULATION OF SATURATION INDEX (SI) 103 APPENDIX B CALIBRATION CURVE ICP-AES 107

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