1、 STD-AWWA M3B-ENGL 1995 0783350 0508229 331 Electrodialysis and EI ec t ro ci ialy sis Reve rsa 1 AWWA MANUAL M38 First Edition I American Water Works Association STDOAWWA M38-ENGL L995 0783350 0508230 033 9 MANUAL OF WATER SUPPLY PRACTICES - M38, First Edition Electrodialysis and Electrodialysis Re
2、versal Copyright O 1995 American Water Works Association All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information or retrieval system, except in the form of brief excerp
3、ts or quotations for review purposes, without the written permission of the publisher. Editor: Phillip Murray Project Managers: Bill Cobban, Kathleen Faller Printed in the United States of America American Water Works Association 6666 West Quincy Avenue Denver, CO 80235 ISBN 0-89867-768-8 Printed on
4、 recycled paper. 11 STD*AWWA fl38-ENGL 1995 0783350 0508231 T7T 9 Contents Preface, v Acknowledgments, vii Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Basic Water Chemistry Concepts, 1 Operating Principles of ED and EDR, 3 Development of ED and EDR Systems, 5
5、 Applications, 10 Chapter2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Components of ED and EDR Design, 13 Staging, 20 Limiting Parameters, 22 Water Recovery, 25 Pretreatment, 26 Operating Principles for Design, 29 Post treatment, 3 1 Concentrate Disposal, 32 Referenc
6、es, 35 Chapter 3 Equipment and Installation . . . . . . , . , . , . . . . . . . . . 37 Equipment Subsystems, 37 Installation, 41 Costing, 42 References, 44 Chapter 4 Operation and Maintenance . . . . . . . . . . . . . . . . . . . . 45 Operation Procedures, 45 Maintenance Requirements, 47 Safety, 52
7、Abbreviations, 55 Additional Sources of Information, 57 Index, 59 . 111 STD-AWWA M3B-ENGL 1775 M 0783350 0508232 706 = Preface This first edition of AWWA Manual M38 provides detailed information on the classical electrodialysis (ED) and the electrodialysis reversal (EDR) processes and systems. ED an
8、d EDR systems employ electrochemical and membrane cell technolo- gies to separate ionic materials in aqueous solutions. These systems have proven useful in food processing, medical applications, and other specialized industrial uses, with major applications being the production of drinking water or
9、pure industrial process water from mineralized sources. Directed to engineers and operators of ED and EDR systems, this manual pro- vides detailed background information on ED and EDR as they relate to water treat- ment processes. The manual explains process principles, equipment information, electr
10、odialysis technology, and system design. Information on water chemistry is included to enhance understanding of water processing. It is hoped that this manual will also assist water process engineers and treat- ment plant decision makers in understanding the value of ED and EDR technology applied to
11、 their water treatment needs. V Previous page is blank STD-AWWA M38-ENGL 1995 0783350 0508233 BY2 Acknowledgments AWWA Manual M38, Electrodialysis and Electrodialysis Reversal, evolved pri- marily from training courses that were given over a six-year period. Several employees of Ionics Inc. of Water
12、town, Mass., contributed to these training courses. Major credit is given to F.H. Meller, who was responsible for organizing information that forms the basis of this manual. Special thanks are extended to E.P. Geishecker, L.R. Siwak, and M.M. Cuzzi, all employees of Ionics, without whose help this m
13、anual would not have been possible. At the time of approval, Membrane Processes Committee members included William J. Conlon (Chair), Camp Dresser A C A C (+) Anode Figure 1-3 Ion exchange membranes in an NaCI solution (DC circuit open) cation transfer membranes (C in Figure 1-31, which are electric
14、ally conductive membranes that are water impermeable and allow only positively charged ions to pass through Varieties of these basic types of membranes exist that are selective to ions that are either monovalent (having a charge magnitude of 1) or divalent (having a charge magnitude of 2). Other typ
15、es can be formulated to enhance the passage rates of selected ions. For example, membranes exist that show an affinity for nitrate passage over other anions. In Figure 1-3 there is no DC potential applied to the electrodes and no movement of ions. Figure 1-4 shows what occurs when DC potential is ap
16、plied across the electrodes. The figure shows six compartments separated by ion exchange membranes. The membranes influence ion behavior as follows: 1. 2. Compartments 1 and 6 - Compartments 1 and 6 contain metal electrodes where reduction and oxidation occur. Compartment 2 - C1- ions pass through t
17、he anion membrane (A) into compartment 3, while Na+ ions move through the cation membrane (C) into compartment 1. STD*AWWA M38-ENGL 1975 M 0763350 0508236 324 = INTRODUCTION 5 I1 2 3 4 5 Cathode (-) Source: Zonics Inc (+) Anode Figure 1-4 DC potential applied across electrodes for an NaCI solution w
18、ith ion exchange membrane 3. Compartment 3 - The Na+ ions cannot move through the anion membrane and remain in compartment 3. The C1- ions cannot pass through the cation membrane and also remain in compartment 3. Compartment 4 - The C1- ions pass through the anion membrane into compartment 5, while
19、Na+ ions pass through the cation membrane into compartment 3. Compartment 5 - The Na+ ions cannot pass through the anion membrane and remain in compartment 5. The C1- ions cannot pass through the cation membrane and remain in compartment 5. 4. 5. Compartments 2 and 4 are depleted of ions, whereas co
20、mpartments 3 and 5 have a higher concentration of ions. When these membranes are properly arranged, two major and separate streams are produced (demineralized and concentrated), as well as two minor streams from the electrode compartments. For water treatment, several hundred of these compartments a
21、re assembled into a membrane stack, forming the heart of an ED system. DEVELOPMENT OF ED AND EDR SYSTEMS ED selectively removes dissolved solids, based on their electrical charge, by transferring the brackish water ions through a semipermeable ion exchange membrane charged with an electrical potenti
22、al. Figure 1-5 shows a schematic of an entire ED system. It points out that the feedwater becomes separated into the following three types of water: (1) product water, which has an acceptably low TDS level; (2) brine, or concentrate, which is the water that receives the brackish water ions; and (3)
23、electrode feedwater, which is the water that passes directly over the electrodes that create the electrical potential. EDR involves reversing the electrical charge to a membrane after a specific interval of time. As described later, this polarity reversal helps prevent the formation of scale on the
24、membranes. Figure 1-6 shows a schematic of an EDR system. The setup is very similar to an ED system except for the presence of reversal valves. Demineralization of brackish water using ED was pioneered in the 1950s. ED has been used successfully over the past 40 years to treat municipal and process
25、water supplies. ED process technology has advanced rapidly since its inception because of improved ion exchange membrane properties, better materials of STDeAWWA M3B-ENGL 1995 0783350 0508239 260 PRV 77 6 ELECTRODIALYSIS :Q y Drain Diversion Valve t Cartridge Filter Inlet Feed Valve Pump PRV U Legen
26、d: C Conductivity Controller PRV Pressure-Regulating Valve Brine Makeup I Membrane Stacks Brine Brine Recycle Pump Product to Waste Brine Blowdown Source: Ionics Inc. Figure 1-5 Electrodialysis system flow diagram t Feed Electrode Feed Degasification Electrode Waste Brine Recycle Pump Legend: C Cond
27、uctivity Controller PRV Pressure-Regulating Valve Source: Ionics Inc. Figure i -6 Electrodialysis reversal system flow diagram STD-AWWA M3B-ENGL 1995 = 0783350 0508240 T82 INTRODUCTION 7 construction, advances in technology, and the evolution of polarity reversal. According to IDA Desalting Plants I
28、nventory,* the installed worldwide capacity of ED and EDR membrane treatment plants increased from 2 mgd (7.5 Mud) in 1955 to more than 200 mgd (750 Mud) in 1992. Custom-designed and prepackaged ED and EDR plants provide water at predetermined TDS or salt-removal levels with high water recovery rate
29、s (i.e., with low amounts of feedwater being sent to waste). Additional production can be achieved by adding process trains or by operating the units in parallel (side by side) rather than in series (one after the other). The desalting capacity can be increased with additional stages of membranes in
30、 series. ED and EDR systems are capable of treating variable source water quality while producing a consistent finished water quality. ED and EDR plants can be designed to remove from 50 to 99 percent of source water contaminants or dissolved solids. Source water salinities of less than 100 mg/L up
31、to 12,000 mgL TDS can be successfully treated to produce finished water of less than 10 mg/L TDS. Batch and Continuous Electrodialysis The first type of commercial ED system was the batch system. In this type of ED system, source water is recirculated from a holding tank through the demineralizing s
32、pacers of a single membrane stack and back to the holding tank until the final purity is obtained. The production rate is dependent on the dissolved minerals concentration in the source water and on the degree of demineralization required. The concentrate stream is also recirculated to reduce wastew
33、ater volume, and continuous addition of acid is required to prevent membrane stack scaling. The second type of commercially available system was the unidirectional continuous-type ED. In this type of system, the membrane stack contains two stages in series; each stage helps demineralize the water. T
34、he demineralized stream makes a single pass through the stack and exits as product water. The concentrate stream is partially recycled to reduce wastewater volume and is injected with acid to prevent scaling. ED systems are unidirectional in the sense that cations move only toward the cathode and an
35、ions move only toward the anode. The current polarity does not reverse. (However, the direction of flow could reverse, and some commercial systems use this technique to deter the buildup of slime and foulants.) In unidirectional ED systems, scale prevention is achieved either by the use of scale inh
36、ibitors for calcium sulfate (Cas041 control and/or acids for carbonates control, or through the use of permselective membranes. Permselective membranes can be tailored to inhibit the passage of divalent anions or cations, such as sulfates, calcium, and magnesium. Permselective refers to the ability
37、of an ED membrane to discriminate between different ions to allow passage or permeation through the membrane. For example, the AST-type membranes show good permeation or high transport numbers for monovalent anions, such as Clk or NOp2, but have low transport numbers and show very low permeation rat
38、es for divalent or trivalent ions, such as s4k2, Pc2, or similar anions. This is achieved by specially treating the anion membrane, and the effect can be exploited to separate various ions. Existing commercial membranes are monovalent anion specific, monovalent cation specific, or hydrogen ion speci
39、fic. The relative specificities vary, with the monovalent anion membrane showing the greatest “Available from the International Desalting Association, Topsdale, Mass. STD-AWWA M3-ENGL 1995 = 0783350 0508243 919 8 ELECTRODIALYSIS specificity, for example, the ratio of chloride to sulfate ion transpor
40、t numbers. Through the use of proper staging, with monovalent and divalent permselective membranes, the development of high calcium sulfate in the concentrate side of the membranes can be forestalled and scale formation prevented. Figures 1-7 and 1-8 illustrate. Figure 1-7 illustrates how a combinat
41、ion of monovalent anion selective membranes in a first stage, followed by a second stage containing monovalent cation permselective membranes, can be used to concentrate solutions well past the normal calcium sulfate solubility limits. In the first stage, no sulfate passes through the membrane, and
42、so the concentrate is rich in calcium chloride. Rather than passing this concentrate to stage 2, the stage 2 system concentrate is made up from fresh feed or another source. Here, the passage of calcium ions is retarded and the concentrate is rich in sodium sulfate. Neither stage ever exceeds the ca
43、lcium sulfate solubility limits. Yet, when the two concentrate streams are combined, together they can far exceed the calcium sulfate limit. In fact, precipitation can result on mixing. Figure 1-8 is a detail of the first stage from Figure 1-7 showing the use of a standard membrane with a monovalent
44、 anion permselective membrane. The concentrate stream is very low in sulfate, about equal to or slightly greater than the feedwater, while the chloride and sodium concentrations, for example, could be many times higher than the feedwater. In other schemes, the concentrate can be made up from a separ
45、ate water source that is already low in sulfate (for example, reverse osmosis permeate or ED dilute water) to increase water recovery. Colloidal particles or slimes that are slightly electronegative may accumulate on the anion membrane and cause membrane fouling. This problem is common to all classe
46、s of ED systems. These fouling agents are removed by flushing with cleaning systems. Control of scale and fouling is critical to all membrane systems - ED, EDR, RO, UF, and others. Costs to install, operate, and maintain chemical feed systems as well Feedwater Monovalent Anion Monovalent Cation Perm
47、selective Membranes Permselective Membranes I Dilute Caso4 Concentrate Source: Thomas D. Wolfe Figure 1-7 Use of monovalent permselective ED membranes for high recovery (concentration of calcium sulfate in saturated waters) STD.AWWA M38-ENGL 1995 0783350 0508242 855 Dilute - To Second Stage or Use I
48、 1 INTRODUCTION 9 (Low SO,) I I Cation Standard Anion Monovalent Membrane Permselective Membrane Source: Thomas D. Wolfe. Figure 1 8 Principle of monovalent permselective electrodialysis as chemical storage facilities can significantly add to the costs of any membrane- based system. Electrodialysis
49、Reversal Electrode compartments in EDR perform differently from those in unidirectional ED. EDR systems, first developed in the 1960s, incorporate electrical polarity reversal to control membrane scaling and fouling. These systems are designed to produce demineralized water continuously without continuous chemical addition during normal operation. In EDR systems, the polarity of the electrodes is reversed two to four times each hour. When polarity is reversed, chemical reactions at the electrodes are reversed. At the negative electrode, reactions produ
