ISO 20468-6:2021
(Main)Guidelines for performance evaluation of treatment technologies for water reuse systems — Part 6: Ion exchange and electrodialysis
Guidelines for performance evaluation of treatment technologies for water reuse systems — Part 6: Ion exchange and electrodialysis
This document provides guidelines on methods for evaluating the performance of ion exchange and electrodialysis for water reuse including ion exchange resin and ion exchange membrane.
Lignes directrices pour l’évaluation des performances des techniques de traitement des systèmes de réutilisation de l’eau — Partie 6: Échange d'ions et électrodialyse
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INTERNATIONAL ISO
STANDARD 20468-6
First edition
2021-06
Guidelines for performance evaluation
of treatment technologies for water
reuse systems —
Part 6:
Ion exchange and electrodialysis
Lignes directrices pour l’évaluation des performances des techniques
de traitement des systèmes de réutilisation de l’eau —
Partie 6: Échange d'ions et électrodialyse
Reference number
ISO 20468-6:2021(E)
©
ISO 2021
---------------------- Page: 1 ----------------------
ISO 20468-6:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 20468-6:2021(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 List of Abbreviated terms . 4
4 Outline of ion exchange and electrodialysis . 5
4.1 General . 5
[11]-[19] 6
4.2 Principle of Ion exchange .
4.2.1 System configuration . 7
4.2.2 Process . 9
[11]-[19] 10
4.3 Principle of Electrodialysis .
4.3.1 System configuration .13
4.3.2 Process .15
4.4 Application examples .16
4.4.1 Ion exchange .16
4.4.2 Electrodialysis .16
4.5 Performance evaluation for ion exchange and electrodialysis .17
[14]-[19]
5 Performance evaluation guideline for ion exchange resin .17
5.1 Performance evaluation .17
5.1.1 Functional requirements .17
5.1.2 Non-functional requirements .17
5.1.3 Timing for evaluating key factors .18
5.2 Evaluation method .19
5.2.1 Ion exchange resin .19
5.2.2 Treated water quality .20
5.2.3 Ion exchange resin tower .20
5.2.4 Operation and maintenance .20
[11]-[18]
6 Performance evaluation guideline for electrodialysis .20
6.1 Performance evaluation .20
6.1.1 Functional requirements .20
6.1.2 Non-functional requirements .21
6.1.3 Timing for evaluating key factors .22
[5],[7],[8],[9] 23
6.2 Evaluation method .
6.2.1 Ion exchange membrane .23
6.2.2 Stack performance .23
6.2.3 Operation and maintenance .24
[20]
Annex A (informative) Main process and typical applications of IER and IEM .26
Annex B (informative) Main treatment technologies and target constituents for reusing water .27
Annex C (informative) Structural model of IER .28
Annex D (informative) Selectivity and selectivity coefficient of IERs .29
Annex E (informative) Comparison of various IERs .31
Annex F (informative) General operation of an IER process .33
[20]
Annex G (informative) Flow diagram of IE and ED process .35
Annex H (informative) Feed water conditions .37
Annex I (informative) Measurement method of electrical resistance of IEM.38
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ISO 20468-6:2021(E)
Annex J (informative) Measurement method of transport number of IEM .40
Annex K (informative) Permselective coefficient of IEM .42
Annex L (informative) Mechanical strength of IEM .43
Annex M (informative) Leak current calculation for a stack .44
Bibliography .46
iv © ISO 2021 – All rights reserved
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ISO 20468-6:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 282, Water reuse, Subcommittee SC 3,
Risk and performance evaluation of water reuse system.
A list of all parts in the ISO 20468 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
© ISO 2021 – All rights reserved v
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ISO 20468-6:2021(E)
Introduction
“Ion exchange” for purification with ion exchange resin and “Electrodialysis” for desalination and
[4]
concentration with ion exchange membrane are classified as “Advanced treatment” in ISO 20468-1 .
Raw water compositions and treated water targets are extremely diverse. Such diversity impedes
making world-wide guidelines for ion exchange and electrodialysis.
Ion exchange resin (IER) provides a medium for ion exchange. Target ions in solution are trapped within
the medium causing other ions contained within the medium to be released into solution. The most
common applications are water softening and water purification.
Electrodialysis (ED) is an ion-separation process that utilizes an electrical potential difference across
ion exchange membrane as the driving force for moving ion in a solution. The membrane is selective
in that it only permits the passage of either anions or cations but not both and can be used to reject
opposite charged ions.
The ISO 20468 series is intended to provide international standards for an objective evaluation
of the performance of ion exchange and electrodialysis. It introduces the concepts of “Functional
requirements” and “Non-functional requirements,” which are suggested and defined in ISO 20468-1,
also used for other water reuse technologies that may be used in combination or alternatively, such as
membrane, UV, and ozone disinfection and distillation.
vi © ISO 2021 – All rights reserved
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INTERNATIONAL STANDARD ISO 20468-6:2021(E)
Guidelines for performance evaluation of treatment
technologies for water reuse systems —
Part 6:
Ion exchange and electrodialysis
1 Scope
This document provides guidelines on methods for evaluating the performance of ion exchange and
electrodialysis for water reuse including ion exchange resin and ion exchange membrane.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 20670, Water reuse — Vocabulary
3 Terms, definitions, and abbreviated terms
For the purposes of this document, the terms and definitions given in ISO 20670 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp
3.1 Terms and definitions
3.1.1
anion exchange membrane
polymer sheet that contain positively charged functional groups in its polymer matrix designed to
conduct anions while blocking other ions
3.1.2
anion exchange resin
polymer beads that contain positively charged functional groups in its polymer matrix capable of
undergoing exchange reactions with anions
3.1.3
bed
packed layers of ion exchange resins (3.1.19)
3.1.4
block
unit composed of cell pairs (3.1.8) and intermediate frame at both ends
Note 1 to entry: Cell-pairs are stacked from several pairs up to thousands of pairs inside an electrodialyser ion
exchange.
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ISO 20468-6:2021(E)
Note 2 to entry: A large number of cell pairs stacked in series causes problems such as non-uniform hydraulic
pressure and increased leak current in an electrodialyser. To prevent such problems, a large electrodialyser is
separated with an intermediate frame (Figure 8).
3.1.5
cation exchange membrane
polymer sheet that contain negatively charged functional groups in its polymer matrix designed to
conduct cations while blocking other ions
3.1.6
cation exchange resin
polymer beads that contain negatively charged functional groups in its polymer matrix capable of
undergoing exchange reactions with cations
3.1.7
cell
thin sheet compartment, through which desalinate (feed water) or concentrate passes
Note 1 to entry: D-cell means a desalinate cell and C-cell means a concentrate cell.
3.1.8
cell pair
series of D-cell (3.1.7), cation exchange membrane (3.1.5), C-cell (3.1.7), and anion exchange membrane
(3.1.1) that are layered in order to constitute a cell pair
Note 1 to entry: A cell pair is the basic unit for desalination and concentration in electrodialysis.
3.1.9
chelating resin
polymer beads that contain functional groups in its polymer matrix capable of forming chelates with
metal ions
3.1.10
current efficiency
ratio of the theoretical to actual current required to transport ions across an ion exchange membrane
(3.1.18)
3.1.11
direct current
unidirectional flow or movement of electrical charge carriers (which are usually electrons)
3.1.12
electrodeionization
water treatment technology that utilizes electricity, ion exchange membranes (3.1.18) and ion exchange
resin (3.1.19) in order to desalinate ions from one solution to another solution in a very low concentration
3.1.13
electrodialysis
water treatment technology that uses ion exchange membranes (3.1.18) in order to move ions from one
solution to another solution by using electrical potential difference
3.1.14
electrodialysis reversal
type of electrodialysis (3.1.13) process that periodically reverses the electrodes polarity, alternating
concentrated and diluted streams, and continuously self-cleaning the scale components
3.1.15
heterogeneous ion exchange membrane
ion exchange membrane (3.1.18) that is obtained by mixing ion exchange resin (3.1.19) and thermoplastic
resin, and has heterogeneous structure
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ISO 20468-6:2021(E)
3.1.16
homogeneous ion exchange membrane
ion exchange membrane (3.1.18) that is uniformly configured except for reinforcement
3.1.17
ion exchange capacity
total quantity of ion exchangeable groups in ion exchange resin (3.1.19)
3.1.18
ion exchange membrane
polymer sheet that contain negatively or positively charged functional groups in its polymer matrix
designed to conduct cations or anions while blocking opposite charged ions
3.1.19
ion exchange resin
polymer beads that contain charged functional groups in its polymer matrix capable of undergoing
exchange reactions with anions or cations
3.1.20
limiting current density
current density beyond which water dissociation will occur
Note 1 to entry: In electrodialysis, ions in a solution migrate from the bulk solution to the surface of an ion
exchange membrane and form a boundary layer having a concentration difference. As current density increases,
the concentration difference of the boundary layer also increases, and the concentration on the surface of the
ion exchange membrane reaches zero. This current density is defined as “Limiting current density (LCD),” and
is an important indicator for deciding the operating current of an electrodialyser. Operation beyond LCD causes
+ -
water to dissociate into hydrogen ions (H ) and hydroxyl ions (OH ) at the ion exchange membrane-surface and
consumes applied current ineffectually.
3.1.21
mixed bed
mixture of anion exchange resin (3.1.2) and cation exchange resins (3.1.6)
3.1.22
particle size and particle size distribution
diameter of ion exchange resin (3.1.19) beads and its distribution
3.1.23
perfect beads content
non-cracked and non-broken bead content in ion exchange resin (3.1.19) beads
3.1.24
reaction rate
ion exchange reaction rate of ion exchange resin (3.1.19)
3.1.25
regeneration
regeneration of ion exchange resin (3.1.19) is a reversal of the exchange reactions with high
concentrations of a regenerate
3.1.26
reverse osmosis (RO)
separation process where one component of a solution is removed from another component by flowing
the feed stream under pressure across a semipermeable membrane that causes selective movement of
solvent against its osmotic pressure difference
Note 1 to entry: Reverse osmosis (RO) removes ions based on electro chemical forces, colloids, and organics
down to 150 molecular weight. May also be called hyperfiltration.
[SOURCE: ASTM D6161-19]
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ISO 20468-6:2021(E)
3.1.27
selectivity coefficient
equilibrium constant for ion exchange reaction in ion exchange resins (3.1.19)
3.1.28
stack
entire body of electrodialyser, assembled with multitude of cell pairs (3.1.8) or several blocks (3.1.4)
between anode cell (3.1.7) and cathode cell (3.1.7), and pair of end plates for tightening
3.1.29
strongly acidic cation exchange resins
resins that have strongly acidic functional groups
3.1.30
strongly basic anion exchange resins
resins that have strongly basic functional groups
3.1.31
transport number
fraction of current carried by a given ion for total current carried by all ions
3.1.32
tower
vessels with packed layers of ion exchange resins (3.1.19) and/or degassers
3.1.33
uniform particle size ion exchange resin
ion exchange resin (3.1.19) that has narrow particle size distribution (3.1.22)
3.1.34
water extractable residue
water soluble extractable residue from ion exchange resins (3.1.19)
3.1.35
water recovery rate
ratio between treated water quantity and feed water quantity to electrodialyser
3.1.36
weakly acidic cation exchange resins
cation exchange resins (3.1.6) that have weakly acidic functional group
3.1.37
weakly basic anion exchange resins
anion exchange resins (3.1.2) that have weakly basic functional group
3.2 List of Abbreviated terms
AC Alternating current
AEM Anion exchange membrane
AER Anion exchange resin
CEM Cation exchange membrane
CER Cation exchange resin
CR Chelating resin
DC Direct current
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ISO 20468-6:2021(E)
EDI Electrodeionization
ED Electrodialysis
EDR Electrodialysis reversal
IE Ion exchange
IEM Ion exchange membrane
IER Ion exchange resin
[7]
LSI Langelier saturation index
LCD Limiting current density
LCR Inductance (L), capacitance (C), and resistance (R) of an electronic component
MB Mixed bed
R Electrical resistance
RO Reverse osmosis
SDI Silt density index
SAC Strongly acidic cation exchange resins
SBA Strongly basic anion exchange resins
TDS Total dissolved solids
WAC Weakly acidic cation exchange resins
WBA Weakly basic anion exchange resins
4 Outline of ion exchange and electrodialysis
4.1 General
IER and IEM use ionic functional groups fixed in polymer beads or in polymer sheets. These fixed ionic
functional groups exchange ions of an opposite charge or selectively transport ions of an opposite
charge. These technologies can be used for many applications including purifying wastewater by passing
it through an IER packed tower, or desalinating and concentrating wastewater with an electrodialyser
in which IEM are equipped. Among these applications, ion exchange in IER and ED in IEM also apply to
water reclamation. Annex A shows the main process and typical applications of IER and IEM.
Ion exchange and ED are one of several technologies (Annex B) that are used for desalination. Table 1
shows typical salinity range of salt removal about IE and ED.
Table 1 — Typical range of salt removal of ion exchange and electrodialysis
Salinity (NaCl) [g/l]
Type Driving Force
Raw Water Desalinate Concentrate
Electrical field
ED 0,5~200 >0,2 <240
& Diffusion
Adsorption & Deso-
IE <1 >0,001 -
rption
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ISO 20468-6:2021(E)
ED, RO, IE and distillation are widely known as a desalination technology. But each strong point is
different. In case of ED, its feature is that both ion concentration and desalination are possible. For
example, in the concentration of seawater, it is possible to concentrate salinity up to about 240g/l
and on the contrary in the desalination, it can be expected to be desalinated about 0,2g/l. It also can
arrange the desalination level. For the desalination purpose, ED is often applicable for brackish water
and ground water.
IE is a purification technology for removing target ions. The purification process is performed by an
adsorption and desorption mechanism. IE is applicable to raw water under 1g/l-TDS and can produce
deionized water and/or ultrapure water. IER is also applicable for decolorizing raw water.
To select an appropriate technology, it is highly recommended to consider the pros and cons of those
technologies. In some cases, a combination of those technologies may contribute great benefits to users
and stakeholders.
EDI is applied to produce pure water or ultrapure water instead of a resin tower or RO. EDI stacks have
an IER or fibre in desalinated chambers to decrease resistivity. As a result, EDI can provide very low
conductivity water.
[11]-[19]
4.2 Principle of Ion exchange
Typical functional groups of IERs are sulfonic acids and quaternary ammoniums, and such IERs are
classified by their functions into CERs, which can exchange cations, and AERs, which can exchange
anions. IERs have spherical crosslinked polymer matrix with functional groups, counter ions, and
hydrated water. These polymer structures affect the ion exchange capacity, reaction rate, and physical
properties of IERs. Annex C shows a structural model of IER.
Ion exchange using IERs depends on a mechanism by which mobile ions from an external solution are
exchanged in the opposite direction for an equivalent number of ions that are electrostatically bound to
functional groups contained within a solid polymer matrix of IERs. Annex D shows the selectivity and
selectivity coefficient of IERs.
The purification process using IER is most commonly performed in cyclic operations of the column
method with an adsorption and desorption mechanism. Each cycle is divided into sorption and
regeneration. Figure 1 shows an outline of an IER tower. Figure 2 shows a representation of an ion
exchange operation cycle.
Key
1 IERs
a
influent
b
effluent
[20]
Figure 1 — Outline of IER tower
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ISO 20468-6:2021(E)
1 sorption
2 regeneration
a
feed water
b
treated water
c
regenerant
d
regeneration wastewater
[20]
Figure 2 — Schematic representation of an ion exchange operation cycle
4.2.1 System configuration
The most important component of IE is IER and the IER tower that equipped with IER.
4.2.1.1 Ion exchange resins
IERs are categorized by their functional groups and physical structure. Typical functional groups of
IERs are sulfonic acids and quaternary ammoniums, and such IERs are classified into CERs and AERs.
IERs have two types of physical structure: gel type and macroporous type. Macroporous type IERs
have high density of macroporous in the polymer matrixes and much larger specific surface areas of the
active surface than gel-type resins.
Table 2 shows types and groups of IERs.
Table 2 — Types and groups of IERs
Grade Functional group Physical structure
1 Gel
Strongly acidic Sulfonic acid
2 CER Macroporous
3 Weakly acidic Carboxylic acid Macroporous
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ISO 20468-6:2021(E)
Table 2 (continued)
Grade Functional group Physical structure
4 Gel
Type I Trimethylammonium
5 Macroporous
Strongly basic
6 AER Gel
Type II Dimethylethanolammonium
7 Macroporous
8 Weakly basic Dimethylamine Macroporous
In addition, IERs are categorized by particle size distribution into two types: polydispersed particle
size IERs and uniform particle size ion exchange resins. Uniform particle size ion exchange resins have
narrower particle size distribution than polydispersed particle size IERs.
Chelating resins are a type of IER with functional groups that can form chelates with metal ions. Table 3
shows types and groups of CRs.
Table 3 — Types and grouping of CRs
Grade Functional group Physical structure Target ions
1 Iminodiacetate Macroporous Heavy metal ions
2 CR Polyamine Macroporous Heavy metal ions
3 Glucamine Macroporous Borate
4.2.1.2 Ion exchange resin tower
IERs are mainly installed in a fixed bed tower. The ion exchange process is composed of IER towers,
feeding unit for raw water and regenerants, and tanks for treated water and wastewater. Figure 3
shows an outline of an IER tower.
8 © ISO 2021 – All rights reserved
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ISO 20468-6:2021(E)
Outside appearance Arrangement of pipings
Key
1 resin bed
2 support plate and strainer
3 flow meter
4 air vent
5 integrating flow meter
a
raw water
b
regenerant
c
treated water
d
wash water
e
backwash waste
[20]
Figure 3 — Outline of an IER tower
4.2.2 Process
4.2.2.1 Process design
Purification processes usin
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 20468-6
ISO/TC 282/SC 3
Guidelines for performance evaluation
Secretariat: JISC
of treatment technologies for water
Voting begins on:
2021-03-11 reuse systems —
Voting terminates on:
Part 6:
2021-05-06
Ion exchange and electrodialysis
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 20468-6:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
©
NATIONAL REGULATIONS. ISO 2021
---------------------- Page: 1 ----------------------
ISO/FDIS 20468-6:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 20468-6:2021(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 List of Abbreviated terms . 4
4 Outline of ion exchange and electrodialysis . 5
4.1 General . 5
[11]-[19] 6
4.2 Principle of Ion exchange .
4.2.1 System configuration . 7
4.2.2 Process . 9
[11]-[19] 10
4.3 Principle of Electrodialysis .
4.3.1 System configuration .13
4.3.2 Process .15
4.4 Application examples .16
4.4.1 Ion exchange .16
4.4.2 Electrodialysis .16
4.5 Performance evaluation for ion exchange and electrodialysis .17
[14]-[19]
5 Performance evaluation guideline for ion exchange resin .17
5.1 Performance evaluation .17
5.1.1 Functional requirements .17
5.1.2 Non-functional requirements .17
5.1.3 Timing for evaluating key factors .18
5.2 Evaluation method .19
5.2.1 Ion exchange resin .19
5.2.2 Treated water quality .20
5.2.3 Ion exchange resin tower .20
5.2.4 Operation and maintenance .20
[11]-[18]
6 Performance evaluation guideline for electrodialysis .20
6.1 Performance evaluation .20
6.1.1 Functional requirements .20
6.1.2 Non-functional requirements .21
6.1.3 Timing for evaluating key factors .22
[5],[7],[8],[9] 23
6.2 Evaluation method .
6.2.1 Ion exchange membrane .23
6.2.2 Stack performance .23
6.2.3 Operation and maintenance .24
[20]
Annex A (informative) Main process and typical applications of IER and IEM .26
Annex B (informative) Main treatment technologies and target constituents for reusing water .27
Annex C (informative) Structural model of IER .28
Annex D (informative) Selectivity and selectivity coefficient of IERs .29
Annex E (informative) Comparison of various IERs .31
Annex F (informative) General operation of an IER process .33
[20]
Annex G (informative) Flow diagram of IE and ED process .35
Annex H (informative) Feed water conditions .37
Annex I (informative) Measurement method of electrical resistance of IEM.38
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ISO/FDIS 20468-6:2021(E)
Annex J (informative) Measurement method of transport number of IEM .40
Annex K (informative) Permselective coefficient of IEM .42
Annex L (informative) Mechanical strength of IEM .43
Annex M (informative) Leak current calculation for a stack .44
Bibliography .46
iv © ISO 2021 – All rights reserved
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ISO/FDIS 20468-6:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 282, Water reuse, Subcommittee SC 3,
Risk and performance evaluation of water reuse system.
A list of all parts in the ISO 20468 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
© ISO 2021 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO/FDIS 20468-6:2021(E)
Introduction
“Ion exchange” for purification with ion exchange resin and “Electrodialysis” for desalination and
[4]
concentration with ion exchange membrane are classified as “Advanced treatment” in ISO 20468-1 .
Raw water compositions and treated water targets are extremely diverse. Such diversity impedes
making world-wide guidelines for ion exchange and electrodialysis.
Ion exchange resin (IER) provides a medium for ion exchange. Target ions in solution are trapped within
the medium causing other ions contained within the medium to be released into solution. The most
common applications are water softening and water purification.
Electrodialysis (ED) is an ion-separation process that utilizes an electrical potential difference across
ion exchange membrane as the driving force for moving ion in a solution. The membrane is selective
in that it only permits the passage of either anions or cations but not both and can be used to reject
opposite charged ions.
The ISO 20468 series is intended to provide international standards for an objective evaluation
of the performance of ion exchange and electrodialysis. It introduces the concepts of “Functional
requirements” and “Non-functional requirements,” which are suggested and defined in ISO 20468-1,
also used for other water reuse technologies that may be used in combination or alternatively, such as
membrane, UV, and ozone disinfection and distillation.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 20468-6:2021(E)
Guidelines for performance evaluation of treatment
technologies for water reuse systems —
Part 6:
Ion exchange and electrodialysis
1 Scope
This document provides guidelines on methods for evaluating the performance of ion exchange and
electrodialysis for water reuse including ion exchange resin and ion exchange membrane.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 20670, Water reuse — Vocabulary
3 Terms, definitions, and abbreviated terms
For the purposes of this document, the terms and definitions given in ISO 20670 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp
3.1 Terms and definitions
3.1.1
anion exchange membrane
polymer sheet that contain positively charged functional groups in its polymer matrix designed to
conduct anions while blocking other ions
3.1.2
anion exchange resin
polymer beads that contain positively charged functional groups in its polymer matrix capable of
undergoing exchange reactions with anions
3.1.3
bed
packed layers of ion exchange resins (3.1.19)
3.1.4
block
unit composed of cell pairs (3.1.8) and intermediate frame at both ends
Note 1 to entry: Cell-pairs are stacked from several pairs up to thousands of pairs inside an electrodialyser ion
exchange.
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ISO/FDIS 20468-6:2021(E)
Note 2 to entry: A large number of cell pairs stacked in series causes problems such as non-uniform hydraulic
pressure and increased leak current in an electrodialyser. To prevent such problems, a large electrodialyser is
separated with an intermediate frame (Figure 8).
3.1.5
cation exchange membrane
polymer sheet that contain negatively charged functional groups in its polymer matrix designed to
conduct cations while blocking other ions
3.1.6
cation exchange resin
polymer beads that contain negatively charged functional groups in its polymer matrix capable of
undergoing exchange reactions with cations
3.1.7
cell
thin sheet compartment, through which desalinate (feed water) or concentrate passes
Note 1 to entry: D-cell means a desalinate cell and C-cell means a concentrate cell.
3.1.8
cell pair
series of D-cell (3.1.7), cation exchange membrane (3.1.5), C-cell (3.1.7), and anion exchange membrane
(3.1.1) that are layered in order to constitute a cell pair
Note 1 to entry: A cell pair is the basic unit for desalination and concentration in electrodialysis.
3.1.9
chelating resin
polymer beads that contain functional groups in its polymer matrix capable of forming chelates with
metal ions
3.1.10
current efficiency
ratio of the theoretical to actual current required to transport ions across an ion exchange membrane
(3.1.18)
3.1.11
direct current
unidirectional flow or movement of electrical charge carriers (which are usually electrons)
3.1.12
electrodeionization
water treatment technology that utilizes electricity, ion exchange membranes (3.1.18) and ion exchange
resin (3.1.19) in order to desalinate ions from one solution to another solution in a very low concentration
3.1.13
electrodialysis
water treatment technology that uses ion exchange membranes (3.1.18) in order to move ions from one
solution to another solution by using electrical potential difference
3.1.14
electrodialysis reversal
type of electrodialysis (3.1.13) process that periodically reverses the electrodes polarity, alternating
concentrated and diluted streams, and continuously self-cleaning the scale components
3.1.15
heterogeneous ion exchange membrane
ion exchange membrane (3.1.18) that is obtained by mixing ion exchange resin (3.1.19) and thermoplastic
resin, and has heterogeneous structure
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ISO/FDIS 20468-6:2021(E)
3.1.16
homogeneous ion exchange membrane
ion exchange membrane (3.1.18) that is uniformly configured except for reinforcement
3.1.17
ion exchange capacity
total quantity of ion exchangeable groups in ion exchange resins (3.1.19)
3.1.18
ion exchange membrane
polymer sheet that contain negatively or positively charged functional groups in its polymer matrix
designed to conduct cations or anions while blocking opposite charged ions
3.1.19
ion exchange resin
polymer beads that contain charged functional groups in its polymer matrix capable of undergoing
exchange reactions with anions or cations
3.1.20
limiting current density
current density beyond which water dissociation will occur
Note 1 to entry: In electrodialysis, ions in a solution migrate from the bulk solution to the surface of an ion
exchange membrane and form a boundary layer having a concentration difference. As current density increases,
the concentration difference of the boundary layer also increases, and the concentration on the surface of the
ion exchange membrane reaches zero. This current density is defined as “Limiting current density (LCD),” and
is an important indicator for deciding the operating current of an electrodialyser. Operation beyond LCD causes
+ -
water to dissociate into hydrogen ions (H ) and hydroxyl ions (OH ) at the ion exchange membrane-surface and
consumes applied current ineffectually.
3.1.21
mixed bed
mixture of anion exchange resins (3.1.2) and cation exchange resins (3.1.6)
3.1.22
particle size and particle size distribution
diameter of ion exchange resins (3.1.19) beads and its distribution
3.1.23
perfect beads content
non-cracked and non-broken bead content in ion exchange resin (3.1.19) beads
3.1.24
reaction rate
ion exchange reaction rate of ion exchange resins (3.1.19)
3.1.25
regeneration
regeneration of ion exchange resins (3.1.19) is a reversal of the exchange reactions with high
concentrations of a regenerate
3.1.26
reverse osmosis (RO)
separation process where one component of a solution is removed from another component by flowing
the feed stream under pressure across a semipermeable that causes selective movement of solvent
against its osmotic pressure difference
Note 1 to entry: Note I to entry: Reverse osmosis (RO) removes ions based on electro chemical forces, colloids,
and organics down to 150 molecular weight. May also be called hyperfiltration.
[SOURCE: ASTM D6161-10]
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ISO/FDIS 20468-6:2021(E)
3.1.27
selectivity coefficient
equilibrium constant for ion exchange reaction in ion exchange resins (3.1.19)
3.1.28
stack
entire body of electrodialyser, assembled with multitude of cell pairs (3.1.8) or several blocks (3.1.4)
between anode cell (3.1.7) and cathode cell (3.1.7), and pair of end plates for tightening
3.1.29
strongly acidic cation exchange resins
resins that have strongly acidic functional groups
3.1.30
strongly basic anion exchange resins
resins that have strongly basic functional groups
3.1.31
transport number
fraction of current carried by a given ion for total current carried by all ions
3.1.32
tower
vessels with packed layers of ion exchange resins (3.1.19) and/or degassers
3.1.33
uniform particle size ion exchange resin
ion exchange resin (3.1.19) that has narrow particle size distribution (3.1.22)
3.1.34
water extractable residue
water soluble extractable residue from ion exchange resins (3.1.19)
3.1.35
water recovery rate
ratio between treated water quantity and feed water quantity to electrodialyser
3.1.36
weakly acidic cation exchange resins
cation exchange resins (3.1.6) that have weakly acidic functional group
3.1.37
weakly basic anion exchange resins
anion exchange resins (3.1.2) that have weakly basic functional group
3.2 List of Abbreviated terms
AC Alternating current
AEM Anion exchange membrane
AER Anion exchange resin
CEM Cation exchange membrane
CER Cation exchange resin
CR Chelating resin
DC Direct current
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ISO/FDIS 20468-6:2021(E)
EDI Electrodeionization
ED Electrodialysis
EDR Electrodialysis reversal
IE Ion exchange
IEM Ion exchange membrane
IER Ion exchange resin
[7]
LSI Langelier saturation index
LCD Limiting current density
LCR Inductance (L), capacitance (C), and resistance (R) of an electronic component
MB Mixed bed
R Electrical resistance
RO Reverse osmosis
SDI Silt density index
SAC Strongly acidic cation exchange resins
SBA Strongly basic anion exchange resins
TDS Total dissolved solids
WAC Weakly acidic cation exchange resins
WBA Weakly basic anion exchange resins
4 Outline of ion exchange and electrodialysis
4.1 General
IER and IEM use ionic functional groups fixed in polymer beads or in polymer sheets. These fixed ionic
functional groups exchange ions of an opposite charge or selectively transport ions of an opposite charge.
These technologies can be used for many applications including purifying wastewater by passing it
through an IER packed tower, or desalinating and concentrating wastewater with an electrodialyser in
which IEM are equipped. Among these applications, ion exchange in IER and electrodialysis in IEM also
apply to water reclamation. Annex A shows the main process and typical applications of IER and IEM.
Ion exchange and electrodialysis are one of several technologies (Annex B) that are used for desalination.
Table 1 shows typical salinity range of salt removal about IE and ED.
Table 1 — Typical range of salt removal of ion exchange and electrodialysis
Salinity (NaCL) [g/l]
Type Driving Force
Raw Water Desalinate Concentrate
Electrical field
ED 0,5~200 >0,2 <240
& Diffusion
Adsorption & Deso-
IE <1 >0,001 -
rption
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ISO/FDIS 20468-6:2021(E)
ED, RO, IE and distillation are widely known as a desalination technology. But each strong point is
different. In case of ED, its feature is that both ion concentration and desalination are possible. For
example, in the concentration of seawater, it is possible to concentrate salinity up to about 240g/l
and on the contrary in the desalination, it can be expected to be desalinated about 0,2g/l. It also can
arrange the desalination level. For the desalination purpose, ED is often applicable for brackish water
and ground water.
IE is a purification technology for removing target ions. The purification process is performed by an
adsorption and desorption mechanism. IE is applicable to raw water under 1g/l-TDS and can produce
deionized water and/or ultrapure water. IER is also applicable for decolorizing raw water.
To select an appropriate technology, it is highly recommended to consider the pros and cons of those
technologies. In some cases, a combination of those technologies may contribute great benefits to users
and stakeholders.
EDI is applied to produce pure water or ultrapure water instead of a resin tower or RO. EDI stacks have
an IER or fibre in desalinated chambers to decrease resistivity. As a result, EDI can provide very low
conductivity water.
[11]-[19]
4.2 Principle of Ion exchange
Typical functional groups of IERs are sulfonic acids and quaternary ammoniums, and such IERs are
classified by their functions into CERs, which can exchange cations, and AERs, which can exchange
anions. IERs have spherical crosslinked polymer matrix with functional groups, counter ions, and
hydrated water. These polymer structures affect the ion exchange capacity, reaction rate, and physical
properties of IERs. Annex C shows a structural model of IER.
Ion exchange using IERs depends on a mechanism by which mobile ions from an external solution are
exchanged in the opposite direction for an equivalent number of ions that are electrostatically bound to
functional groups contained within a solid polymer matrix of IERs. Annex D shows the selectivity and
selectivity coefficient of IERs.
The purification process using IER is most commonly performed in cyclic operations of the column
method with an adsorption and desorption mechanism. Each cycle is divided into sorption and
regeneration. Figure 1 shows an outline of an IER tower. Figure 2 shows a representation of an ion
exchange operation cycle.
Key
1 IERs
a
Influent.
b
Effluent.
[20]
Figure 1 — Outline of IER tower
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ISO/FDIS 20468-6:2021(E)
1 sorption
2 regeneration
a
Feed water.
b
Treated water.
c
Regenerant.
d
Regeneration wastewater.
[20]
Figure 2 — Schematic representation of an ion exchange operation cycle
4.2.1 System configuration
The most important component of IE is IER and the IER tower that equipped with IER.
4.2.1.1 Ion exchange resins
IERs are categorized by their functional groups and physical structure. Typical functional groups of
IERs are sulfonic acids and quaternary ammoniums, and such IERs are classified into CERs and AERs.
IERs have two types of physical structure: gel type and macroporous type. Macroporous type IERs
have high density of macroporous in the polymer matrixes and much larger specific surface areas of the
active surface than gel-type resins.
Table 2 shows types and groups of IERs.
Table 2 — Types and groups of IERs
Grade Functional group Physical structure
1 Gel
Strongly acidic Sulfonic acid
2 CER Macroporous
3 Weakly acidic Carboxylic acid Macroporous
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ISO/FDIS 20468-6:2021(E)
Table 2 (continued)
Grade Functional group Physical structure
4 Gel
Type I Trimethylammonium
5 Macroporous
Strongly basic
6 AER Gel
Type II Dimethylethanolammonium
7 Macroporous
8 Weakly basic Dimethylamine Macroporous
In addition, IERs are categorized by particle size distribution into two types: polydispersed particle
size IERs and uniform particle size ion exchange resins. Uniform particle size ion exchange resins have
narrower particle size distribution than polydispersed particle size IERs.
Chelating resins are a type of IER with functional groups that can form chelates with metal ions. Table 3
shows types and groups of CRs.
Table 3 — Types and grouping of CRs
Grade Functional group Physical structure Target ions
1 Iminodiacetate Macroporous Heavy metal ions
2 CR Polyamine Macroporous Heavy metal ions
3 Glucamine Macroporous Borate
4.2.1.2 Ion exchange resins tower
IERs are mainly installed in a fixed bed tower. The ion exchange process is composed of IER towers,
feeding unit for raw water a
...
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