ISO 20468-5:2021
(Main)Guidelines for performance evaluation of treatment technologies for water reuse systems — Part 5: Membrane filtration
Guidelines for performance evaluation of treatment technologies for water reuse systems — Part 5: Membrane filtration
This document provides guidelines for performance evaluation methods of water reclamation systems using membrane technologies. This document provides guidance in ensuring treated wastewater quality levels at the point of exit from the membrane filtration processes. It also provides potential methods for evaluating the environmental and economic performance of membrane filtration processes in water reuse. This document helps plant designers, operators and end users to effectively design and operate the membrane-based water reclamation systems.
Lignes directrices pour l’évaluation des performances des techniques de traitement des systèmes de réutilisation de l’eau — Partie 5: Filtration sur membrane
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INTERNATIONAL ISO
STANDARD 20468-5
First edition
2021-06
Guidelines for performance evaluation
of treatment technologies for water
reuse systems —
Part 5:
Membrane filtration
Lignes directrices pour l’évaluation des performances des techniques
de traitement des systèmes de réutilisation de l’eau —
Partie 5: Filtration sur membrane
Reference number
ISO 20468-5:2021(E)
©
ISO 2021
---------------------- Page: 1 ----------------------
ISO 20468-5:2021(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 20468-5:2021(E)
Contents Page
Foreword .iv
Introduction .v
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 Concepts of membrane filtration technology for water reuse . 5
4.1 General . 5
4.2 Membrane type and treatment objectives . 5
4.3 Filtration unit process . 6
4.4 Membrane filtration process design and pre- and post-shipment tests . 7
5 Principles and general guidelines for performance evaluation . 7
5.1 General . 7
5.2 Functional requirements for membrane filtration process. 7
5.3 Non-functional requirements for membrane filtration process . 8
6 Performance evaluation for functional requirement. 8
6.1 General . 8
6.2 Water quality based performance evaluation . 8
6.3 Process based performance evaluation . 9
6.4 Integrity monitoring. 9
6.4.1 Direct Integrity Monitoring . 9
6.4.2 Indirect integrity monitoring .11
7 Performance evaluation for non-functional requirements .12
7.1 General .12
7.2 Energy consumption .12
7.3 Chemical consumption .13
7.4 Brine water disposal or treatment.13
7.5 Solid waste for disposal .14
7.6 Life cycle cost.14
Annex A (informative) Examples of parameters on the specification sheet .15
Annex B (informative) Recommended frequency of data collection .17
Annex C (informative) .18
Bibliography .19
© ISO 2021 – All rights reserved iii
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ISO 20468-5:2021(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 on 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 the following
URL: 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 systems.
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.
iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 20468-5:2021(E)
Introduction
Guidelines for performance evaluation of water reclamation systems are essential for municipalities,
utilities and reclaimed water users to meet water quality requirements without compromising public
health. ISO 20468-1, Guidelines for performance evaluation of treatment technologies for water reuse
systems specifies fundamental requirements for the overall water reuse system, which mainly focuses
on the finished water quality. When operating a water reclamation system, performance evaluations
at the point of an individual water reclamation process, helps to provide early warnings to enable
operator response in avoiding adverse impacts on public health, and to comply with the targets of final
water quality. It is particularly important for membrane-based water reclamation processes that are
often employed as the most important barriers for the removal of major constituents in wastewater
(e.g. particulates, dissolved solids, and pathogens). In addition, guidelines for performance evaluation
of individual treatment processes in terms of environmental and economic performances can also
assist decisions on the appropriate selection of water reclamation technologies, which is of paramount
importance in water reuse. This document is intended to provide stakeholders typical performance
evaluation approaches designed for membrane filtration technologies. In addition, this document is
expected to assist the development and operation of water reuse projects, in which process designers,
plant managers, and operators are involved. Similar to ISO 20468-1, this document is mainly comprised
of functional and non-functional requirements for the performance evaluation of membrane filtration
technologies.
© ISO 2021 – All rights reserved v
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INTERNATIONAL STANDARD ISO 20468-5:2021(E)
Guidelines for performance evaluation of treatment
technologies for water reuse systems —
Part 5:
Membrane filtration
1 Scope
This document provides guidelines for performance evaluation methods of water reclamation systems
using membrane technologies. This document provides guidance in ensuring treated wastewater
quality levels at the point of exit from the membrane filtration processes. It also provides potential
methods for evaluating the environmental and economic performance of membrane filtration processes
in water reuse. This document helps plant designers, operators and end users to effectively design and
operate the membrane-based water reclamation systems.
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 20670:2018, 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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1 Terms and definitions
3.1.1
backwash
reverse flow of water with/without air across a membrane (i.e. from permeate side to feed side)
Note 1 to entry: It is designated to remove the deposited foreign substances (foulants) from the membrane.
3.1.2
bubble point pressure
pressure differential at which bubbles first appear on one surface of an immersed porous membrane, as
pressure is applied to the other side
3.1.3
cleaning
operation during which membranes are cleaned using a membrane cleaning system with or without
chemical reagents
EXAMPLE backwashing, flushing, chemical cleaning.
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ISO 20468-5:2021(E)
[SOURCE: AWWA B110-09]
3.1.4
concentrate
rejected stream exiting a membrane module under a cross-flow (3.1.5) mode
Note 1 to entry: Concentrate stream contains increased concentrations of constituents over the feed stream due
to the accumulation of rejected constituents by membranes in the feed stream.
3.1.5
cross-flow
flow orientation through a membrane module in which the fluid on the upstream side of the membrane
moves parallel to the membrane surface
Note 1 to entry: Fluid on the downstream side of the membrane moves away from the membrane in the direction
normal to the membrane surface.
[SOURCE: AWWA B130-13]
3.1.6
dead-end flow
flow through a membrane module in which the only outlet for the upstream fluid is through the
membrane
[SOURCE: ASTM D6161-19]
3.1.7
feed
input solution entering the inlet of a membrane module or system
3.1.8
flux
membrane throughput, usually expressed in volume of permeate (3.1.17) per unit time per unit
2
membrane surface area such as litre per square meter per hour (l/m /hr) at a given temperature or
normalized temperature (more often 20 °C)
Note 1 to entry: It can also be expressed in number of moles, volume or mass of a specified component per unit
time per unit membrane surface area.
3.1.9
fouling
processes leading to deterioration of membrane flux due to surface or internal blockage of the
membrane
[SOURCE: AWWA B130-13]
3.1.10
integrity test
non-destructive physical test that can be correlated to the membrane retention capability of the
membrane system to ensure that membrane system is free of physical defect
3.1.11
membrane integrity
relative degree to which a membrane successfully rejects or retains specific target constituents while
allowing water to pass through
2 © ISO 2021 – All rights reserved
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ISO 20468-5:2021(E)
3.1.12
membrane bioreactor (MBR)
integrated wastewater treatment process combining a suspended growth biological treatment and a
membrane filtration system (UF/MF membrane) replacing conventional secondary clarifier
Note 1 to entry: MF or UF membrane is submerged in biological reactor (submerged MBR). Another configuration
has pressurized membrane modules externally coupled to the bioreactor, with the biomass recirculated between
the membrane modules and the bioreactor by pumping (side-stream MBR).
3.1.13
microfiltration (MF)
pressure driven membrane based separation process designed to remove particles and macromolecules
in the approximate range of 0,05 to 2 μm
[SOURCE: ASTM D6161-19]
3.1.14
molecular weight cut-off
rating of a membrane based on the size of uncharged solutes that is typically 90 % retained by a
membrane
Note 1 to entry: It is also referred to as nominal molecular weight cut-off (NMWCO).
Note 2 to entry: MWCO is typically expressed in Daltons.
[SOURCE: AWWA B130-13]
3.1.15
nanofiltration (NF)
cross-flow (3.1.5) process with pore sizes designed to remove selected salts and most organics above
about 300 Daltons molecular weight range
Note 1 to entry: Nanoflitration (NF) is sometimes referred as loose RO.
Note 2 to entry: Nanofiltration (NF) is a pressure driven separation process in which particles and dissolved
molecules smaller than about 2 nm are rejected.
[SOURCE: ASTM D6161-19]
3.1.16
permeate
portion of the feed stream which passes through a membrane
[SOURCE: ASTM D6161-19]
3.1.17
permeability
ability of a membrane barrier to allow the passage or diffusion of a substance (i.e., a gas, a liquid, or
solute), also a numerical value used to measure water flow through a MF/UF/NF/RO membrane, usually
expressed in volume of permeate (3.1.17) per unit membrane surface area per unit time per unit
2
pressure such as litres per square meter per hour per bar (l/m /hr/bar) at a given temperature and
typically corrected (normalized) to a constant temperature (20 °C or 25 °C)
Note 1 to entry: It is also referred to as specific flux.
[SOURCE: AWWA M53]
3.1.18
pore size
size of the openings in a porous membrane, expressed either in a nominal (average) or absolute
(maximum) value, typically measured in μm
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ISO 20468-5:2021(E)
3.1.19
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 Daltons molecular weight. May also be called hyperfiltration.
[SOURCE: ASTM D6161-19]
3.1.20
silt density index (SDI)
index for the fouling capacity of water in reverse osmosis systems, measuring the rate at which a
0,45-micrometre filter is plugged when subjected to a constant water pressure of 206,8 kPa (30 psi)
[SOURCE: ASTM D4189-07 (2014)]
3.1.21
transmembrane pressure
hydraulic pressure differential (net driving force) across the membrane
[SOURCE: ASTM D6161-19]
3.1.22
ultrafiltration (UF)
pressure driven process employing semipermeable membrane under hydraulic pressure gradient for
the separation components in a solution
Note 1 to entry: The pores of the membrane are of a size smaller than 0,1 μm, which allows passage of the
solvent(s) but will retain non-ionic solutes based primarily on physical size, not chemical potential.
[SOURCE: ASTM D6161-19]
3.2 List of abbreviated terms
BOD Biochemical oxygen demand
COD Chemical oxygen demand
LCC Life cycle cost
MBR Membrane bioreactor
MF Microfiltration
MLSS Mixed liquor suspended solids
MWCO Molecular weight cut off
NF Nanofiltration
NTU Nephelometric turbidity units
RO Reverse osmosis
SDI Silt density index
SS Suspended solids
TMP Transmembrane pressure
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ISO 20468-5:2021(E)
TOC Total organic carbon
TSS Total suspended solids
UF Ultrafiltration
4 Concepts of membrane filtration technology for water reuse
4.1 General
This clause outlines the fundamentals of membrane filtration technologies in water reuse. Membrane
filtration is a viable and recognized technology as physical barrier in water reuse with its high
separation performance. Many of recent water reclamation schemes have employed membrane
filtration processes in combination with other processes for the removal of multiple constituents in
wastewater (see Table 1.)
Table 1 — Membrane types and targeted contaminants
Type TMP, approximate range (MPa) Contaminants targeted for removal
MF < 0,2 0,07 – 1,0 μm diameter particle: TSS, Turbidity, at least 4-log
reduction in protozoa, bacteria, but not viruses
UF 0,05 – 0,5 0,008 – 0,05 μm: TSS, turbidity, macromolecules, colloidal par-
ticles, at least 4 to 6-log reduction in protozoa, bacteria, and 1
to 6-log reduction in viruses
NF 0,5 - 3 0,001 to 0,02 μm: Pesticides and other macromolecules (high
molecular weight) organics, color, colloids, all pathogen groups
and polyvalent cations
RO 0,5 - 7 0,0001 to 0,002 μm: dissolved salts, colloids, low molecular
weight organics, color, TDS, mono and multi valent ions (e.g.
chlorides, sulfates, nitrate, sodium, boron, metals, other ions)
4.2 Membrane type and treatment objectives
Membrane type is typically classified into four categories depending on levels of their pore size for MF
and UF membranes and their separation capabilities for NF and RO membranes (see Table 1). Driving
force of solution through these membranes is a pressure difference across feed and permeate streams.
MF/UF membrane filtration processes in water reuse are generally used to remove suspended particles
including particulates, and colloids. In water reclamation, MF/UF processes effectively work as an
alternative process of secondary clarifiers and media filters that are a subsequent process of biological
treatment. With their high separation capability for particles, they are often used as a pre-treatment
of NF/RO process for fouling mitigation. MF membranes can achieve high removal of suspended solids,
large pathogens (i.e. bacteria and protozoa) and some viruses. UF membranes, which have smaller
nominal pore size than MF membranes, are in addition capable of removing small constituents in
wastewater such as viruses and macromolecules.
MF/UF incorporated with a biological process is referred to as a MBR process.
NF/RO membranes have capabilities for producing high-quality reclaimed water which is suitable for
many industrial uses and many applications with a high likelihood of human contact. NF membranes
can effectively remove multivalent ions including heavy metals and most micropollutants (e.g. >200–
300 molecular weight). RO membranes can remove monovalent ions including sodium and chloride ions
and low molecular weight micropollutants (e.g. <200–300 molecular weight). NF/RO membrane spiral
wound elements are typically housed in a pressure vessel and their processes are usually operated
continuously; thus, it is required to undergo sufficient pre-treatment to mitigate membrane fouling
(e.g. target SDI in RO feed <3). Downstream to the pressure driven membrane process, disinfection
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ISO 20468-5:2021(E)
could be required as a safety barrier to ensure the redundancy and the very high reliability of the water
treatment.
4.3 Filtration unit process
There are two types of membrane filtration: Pressure driven filtration and Vacuum driven filtration
(see Figure 1). In a pressure driven filtration configuration, driving force for filtration is generated by
additional pressure generated by a pump installed in the feed stream. In a vacuum driven filtration
configuration, driving force for filtration is generated by suction pump installed in the permeate
stream.
There are two types of pressure driven filtration modes: cross-flow mode and dead-end mode. In a
cross-flow filtration process, most feed flow travels tangentially to the membrane surface for scouring
foulants from the membrane surface and minimizing concentration polarization. Because NF/RO
processes require high pressure due to the tightness of free-volume holes and the influence of osmotic
pressure, almost all NF/RO membranes are housed in pressure vessels and are operated under pressure
in a cross-flow orientation. In a dead-end filtration process, no cross-flow occurs, meaning that feed
flow rate equals permeate flow rate. For MF/UF, intermittent backwash with permeate and/or air is
made to recover the flux decline.
In a vacuum driven filtration process, membrane modules are immersed in an open basin, in which
feed water is introduced. In MBR, MF or UF membranes are used in a vacuum driven configuration in
an aeration tank and the driving force (i.e. pressure difference) is generated by a vacuum pump in the
permeate stream.
(a) Pressure-driven filtration
(b) Vacuum-driven filtration
6 © ISO 2021 – All rights reserved
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ISO 20468-5:2021(E)
Key
A cross flow
B dead-end flow
1 feed
2 feed pump
3 permeate
4 (backwash)
5 membrane module(s)
6 concentrate
7 concentrate (recirculate)
8 recirculation pump
9 tank
10 blower
11 suction pump
Figure 1 — Typical Membrane filtration systems
4.4 Membrane filtration process design and pre- and post-shipment tests
Successful system design and constructions of membrane filtration processes for water reuse can
be achieved by appropriate membrane selections. It is important for engineers to design membrane
filtration systems after verifying the membrane specifications such as pore size, pure water permeability,
separation performance, a range of information including membrane configuration, material, operating
conditions and cleaning methods. Further details of the membrane specifications are provided
in Annex A. Before shipment, during membrane reception on site, and during commissioning, the
membrane modules/elements are typically evaluated by confirming the proper storage conditions and
whether they meet the product specifications. If required, proper storage conditions of the membrane
on site before commissioning shall be anticipated.
5 Principles and general guidelines for performance evaluation
5.1 General
The purpose of performance evaluation for membrane filtration technology is to determine whether
membrane filtration processes can consistently meet specified membrane performance requirements.
Clause 5 defines two key performance requirements in membrane performance evaluation: functional
and non-functional requirements. Performance requirements are evaluated using specified test
protocols that include sample collection methods, monitoring methods, ancillary data collection
frequency and methods, documentation and valid data analysis procedures, and their details will be
described in Clauses 6 and 7.
5.2 Functional requirements for membrane filtration process
Functional requirements for membrane filtration technology address the rejection of constituents
in the feed water to produce a highly-treated wastewater that meets the reclaimed water quality
requirements. Performance evaluation for functional requirements in membrane filtration process
are categorized (1) water quality-based performance evaluation, (2) process based performance
evaluation, and (3) integrity testing.
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ISO 20468-5:2021(E)
5.3 Non-functional requirements for membrane filtration process
Non-functional requirements involve environmental and economic performance. Environmental
performance evaluation for membrane filtration process can be conducted with energy consumption,
chemical consumption, and volume of liquid and solid wastes. Economic performance evaluation for
membrane filtration technology can be based on LCC, which includes capital cost and operating cost.
6 Performance evaluation for functional requirement
6.1 General
Performance evaluation for water reclamation is primarily conducted through water quality analysis
of the finished (reclaimed) water to ensure the compliance for reclaimed water quality requirements
that are typically regulated at the end of water treatment trains (or at the exit of the water reclamation
plant). However, monitoring water quality at a unit process (e.g. membrane filtration) provides
additional confidence and alerts to non-compliance with the water quality requirements. It also acts as
an early warning to identify any water quality-related issues that may occur between routine samplings
of the finished water.
When a membrane is used for a long period of time, the membrane module may be damaged due to physical
defects or chemical deterioration. This can cause a deterioration in membrane separation performance
but may not be apparent in monitored water quality. Therefore, the performance evaluation based on
the water quality analysis is typically supplemented by other performance evaluation methods that
enable to monitor the membrane integrity during the system operation. These methods include direct
integrity monitoring and indirect integrity monitoring. Direct integrity monitoring is an accurate and
reliable strategy which is able to identify minor deterioration in various applications requiring high-
quality water. Indirect integrity monitoring involves surrogate measurement of membrane integrity,
which is not as sensitive as direct integrity monitoring but can be readily applied to any types of
membrane filtration systems regardless of manufacturer’s specifications. It often provides online or
real-time indication of membrane integrity.
In order to make the operation of membrane filtration process
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 20468-5
ISO/TC 282/SC 3
Guidelines for performance evaluation
Secretariat: JISC
of treatment technologies for water
Voting begins on:
2021-03-12 reuse systems —
Voting terminates on:
Part 5:
2021-05-07
Membrane filtration
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 20468-5:2021(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 20468-5:2021(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 20468-5:2021(E)
Contents Page
Foreword .iv
Introduction .v
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 Concepts of membrane filtration technology for water reuse . 5
4.1 General . 5
4.2 Membrane type and treatment objectives . 5
4.3 Filtration unit process . 6
4.4 Membrane filtration process design and pre- and post-shipment tests . 7
5 Principles and general guidelines for performance evaluation . 7
5.1 General . 7
5.2 Functional requirements for membrane filtration process. 7
5.3 Non-functional requirements for membrane filtration process . 8
6 Performance evaluation for functional requirement. 8
6.1 General . 8
6.2 Water quality based performance evaluation . 8
6.3 Process based performance evaluation . 9
6.4 Integrity monitoring. 9
6.4.1 Direct Integrity Monitoring . 9
6.4.2 Indirect integrity monitoring .11
7 Performance evaluation for non-functional requirements .12
7.1 General .12
7.2 Energy consumption .12
7.3 Chemical consumption .13
7.4 Brine water disposal or treatment.13
7.5 Solid waste for disposal .14
7.6 Life cycle cost.14
Annex A (informative) Examples of parameters on the specification sheet .15
Annex B (informative) Recommended frequency of data collection .16
Annex C (informative) .17
Bibliography .18
© ISO 2021 – All rights reserved iii
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ISO/FDIS 20468-5:2021(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 on 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 the following
URL: 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 systems.
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.
iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/FDIS 20468-5:2021(E)
Introduction
Guidelines for performance evaluation of water reclamation systems are essential for municipalities,
utilities and reclaimed water users to meet water quality requirements without compromising public
health. ISO 20468-1, Guidelines for performance evaluation of treatment technologies for water reuse
systems specifies fundamental requirements for the overall water reuse system, which mainly focuses
on the finished water quality. During the operation of a water reclamation system, performance
evaluation at the point of individual water reclamation process helps to provide early warnings
to operators to avoid adverse health impact on public health and to comply with the targets of final
water quality. It is particularly important for membrane-based water reclamation processes that are
often employed as the most important barriers for the removal of major constituents in wastewater
(e.g. particulates, dissolved solids, and pathogens). In addition, guidelines for performance evaluation
of individual treatment processes in terms of environmental and economic performances can also
assist decisions on the appropriate selection of water reclamation technologies, which is of paramount
importance in water reuse. This document is intended to provide stakeholders typical performance
evaluation approaches designed for membrane filtration technologies. In addition, this document is
expected to assist the development and operation of water reuse projects, in which process designers,
plant managers, and operators are involved. Similar to ISO 20468-1, this document is mainly comprised
of functional and non-functional requirements for the performance evaluation of membrane filtration
technologies.
© ISO 2021 – All rights reserved v
---------------------- Page: 5 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 20468-5:2021(E)
Guidelines for performance evaluation of treatment
technologies for water reuse systems —
Part 5:
Membrane filtration
1 Scope
This document provides guidelines for performance evaluation methods of water reclamation systems
using membrane technologies. This document provides guidance in ensuring treated wastewater
quality levels at the point of exit from the membrane filtration processes. It also provides potential
methods for evaluating the environmental and economic performance of membrane filtration processes
in water reuse. This document helps plant designers, operators and end users to effectively design and
operate the membrane-based water reclamation systems.
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
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ISO 20670:2018, 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.
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3.1 Terms and definitions
3.1.1
backwash
reverse flow of water with/without air across a membrane (i.e. from permeate side to feed side)
Note 1 to entry: It is designated to remove the deposited foreign substances (foulants) from the membrane.
3.1.2
bubble point pressure
pressure differential at which bubbles first appear on one surface of an immersed porous membrane, as
pressure is applied to the other side
3.1.3
cleaning
operation during which membrane is cleaned using a membrane cleaning system with or without
chemical reagents
EXAMPLE backwashing, flushing, chemical cleaning.
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[SOURCE: AWWA B110-09]
3.1.4
concentrate
rejected stream exiting a membrane module under a cross-flow (3.1.5) mode
Note 1 to entry: Note to entry: Concentrate stream contains increased concentrations of constituents over the
feed stream due to the accumulation of rejected constituents by membranes in the feed stream.
3.1.5
cross-flow
flow orientation through a membrane module in which the fluid on the upstream side of the membrane
moves parallel to the membrane surface
Note 1 to entry: Fluid on the downstream side of the membrane moves away from the membrane in the direction
normal to the membrane surface.
[SOURCE: AWWA B130-13]
3.1.6
dead-end flow
flow through a membrane module in which the only outlet for the upstream fluid is through the
membrane
[SOURCE: ASTM D6161-19]
3.1.7
feed
input solution entering the inlet of a membrane module or system
3.1.8
flux
membrane throughput, usually expressed in volume of permeate (3.1.17) per unit time per unit
2
membrane surface area such as litres per square meters per hour (l/m /hr) at a given temperature or
normalized temperature (more often 20 °C)
Note 1 to entry: It can also be expressed in number of moles, volume or mass of a specified component per unit
time per unit membrane surface area.
3.1.9
fouling
processes leading to deterioration of membrane flux due to surface or internal blockage of the
membrane
[SOURCE: AWWA B130-13]
3.1.10
integrity test
non-destructive physical test that can be correlated to the membrane retention capability of the
membrane system to ensure that membrane system is free of physical defect
3.1.11
membrane integrity
relative degree to which a membrane successfully rejects or retains specific target constituents while
allowing water to pass through
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3.1.12
membrane bioreactor (MBR)
integrated wastewater treatment process combining a suspended growth biological treatment and a
membrane filtration system (UF/MF membrane) replacing conventional secondary clarifier
Note 1 to entry: MF or UF membrane is submerged in biological reactor (submerged MBR). Another configuration
has pressurized membrane modules externally coupled to the bioreactor, with the biomass recirculated between
the membrane modules and the bioreactor by pumping (side-stream MBR).
3.1.13
microfiltration (MF)
pressure driven membrane based separation process designed to remove particles and macromolecules
in the approximate range of 0,05 to 2 μm
[SOURCE: ASTM D6161-19]
3.1.14
molecular weight cut-off
rating of a membrane based on the size of uncharged solutes that is typically 90 % retained by a
membrane
Note 1 to entry: It is also referred to as nominal molecular weight cut-off (NMWCO).
Note 2 to entry: MWCO is typically expressed in Daltons.
[SOURCE: AWWA B130-13]
3.1.15
nanofiltration (NF)
cross-flow (3.1.5) process with pore sizes designed to remove selected salts and most organics above
about 300 molecular weight range
Note 1 to entry: Nanoflitration (NF) is sometimes referred as loose RO.
Note 2 to entry: Nanofiltration (NF) is a pressure driven separation process in which particles and dissolved
molecules smaller than about 2 nm are rejected.
[SOURCE: ASTM D6161-19]
3.1.16
permeate
portion of the feed stream which passes through a membrane
[SOURCE: ASTM D6161-19]
3.1.17
permeability
ability of a membrane barrier to allow the passage or diffusion of a substance (i.e., a gas, a liquid, or
solute), also a numerical value used to measure water flow through a MF/UF/NF/RO membrane, usually
expressed in volume of permeate (3.1.17) per unit membrane surface area per unit time per unit
2
pressure such as litters per square meter per hour per bar (l/m /hr/bars) at a given temperature and
typically corrected (normalized) to a constant temperature (20 °C or 25 °C)
Note 1 to entry: It is also referred to as specific flux.
[SOURCE: AWWA M53]
3.1.18
pore size
size of the openings in a porous membrane, expressed either in a nominal (average) or absolute
(maximum) value, typically measured in μm
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3.1.19
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: 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]
3.1.20
silt density index (SDI)
index for the fouling capacity of water in reverse osmosis systems, measuring the rate at which a
0,45-micrometre filter is plugged when subjected to a constant water pressure of 206,8 kPa (30 psi)
[SOURCE: ASTM D4189-07 (2014)]
3.1.21
transmembrane pressure
hydraulic pressure differential (net driving force) across the membrane
[SOURCE: ASTM D6161-10]
3.1.22
ultrafiltration (UF)
pressure driven process employing semipermeable membrane under hydraulic pressure gradient for
the separation components in a solution
Note 1 to entry: Note to entry: The pores of the membrane are of a size smaller than 0,1 μm, which allows passage
of the solvent(s) but will retain non-ionic solutes based primarily on physical size, not chemical potential.
[SOURCE: ASTM D6161-19]
3.2 List of abbreviated terms
BOD Biochemical oxygen demand
COD Chemical oxygen demand
LCC Life cycle cost
MBR Membrane bioreactor
MF Microfiltration
MLSS Mixed liquor suspended solids
MWCO Molecular weight cut off
NF Nanofiltration
NTU Nephelometric turbidity units
RO Reverse osmosis
SDI Silt density index
SS Suspended solids
TMP Transmembrane pressure
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TOC Total organic carbon
TSS Total suspended solids
UF Ultrafiltration
4 Concepts of membrane filtration technology for water reuse
4.1 General
This clause outlines the fundamentals of membrane filtration technologies in water reuse. Membrane
filtration is a viable and recognized technology as physical barrier in water reuse with its high
separation performance. Many of recent water reclamation schemes have employed membrane
filtration processes in combination with other processes for the removal of multiple constituents in
wastewater (see Table 1.)
Table 1 — Membrane types and targeted contaminants
Type TMP, approximate range (MPa) Contaminants targeted for removal
MF < 0,2 0,07 – 1,0 μm diameter particle: TSS, Turbidity, at least 4-log
reduction in protozoa, bacteria, but not viruses
UF 0,05 – 0,5 0,008 – 0,05 μm: TSS, turbidity, macromolecules, colloidal par-
ticles, at least 4 to 6-log reduction in protozoa, bacteria, and 1
to 6-log reduction in viruses
NF 0,5 - 3 0,001 to 0,02 μm: Pesticides and other macromolecules (high
molecular weight) organics, color, colloids, all pathogen groups
and polyvalent cations.
RO 0,5 - 7 0,0001 to 0,002 μm: dissolved salts, colloids, low molecular
weight organics, color, TDS, mono and multi valent ions (e.g.
chlorides, sulfates, nitrate, sodium, boron, metals, other ions)
4.2 Membrane type and treatment objectives
Membrane type is typically classified into four categories depending on levels of their pore size for MF
and UF membranes and their separation capabilities for NF and RO membranes (see Table 1). Driving
force of solution through these membranes is a pressure difference across feed and permeate streams.
MF/UF membrane filtration processes in water reuse are generally used to remove suspended particles
including particulates, and colloids. In water reclamation, MF/UF processes effectively work as an
alternative process of secondary clarifiers and media filters that are a subsequent process of biological
treatment. With their high separation capability for particles, they are often used as a pre-treatment
of NF/RO process for fouling mitigation. MF membranes can achieve high removal of suspended solids,
large pathogens (i.e. bacteria and protozoa) and some viruses. UF membranes, which have smaller
nominal pore size than MF membranes, are in addition capable of removing small constituents in
wastewater such as viruses and macromolecules.
MF/UF incorporated with a biological process is referred to as a MBR process.
NF/RO membranes have capabilities for producing high-quality reclaimed water which is suitable for
many industrial uses and many applications with a high likelihood of human contact. NF membranes
can effectively remove multivalent ions including heavy metals and most micropollutants (e.g. >200–
300 molecular weight). RO membranes can remove monovalent ions including sodium and chloride ions
and low molecular weight micropollutants (e.g. <200–300 molecular weight). NF/RO membrane spiral
wound elements are typically housed in a pressure vessel and their processes are usually operated
continuously; thus, it is required to undergo sufficient pre-treatment to mitigate membrane fouling
(e.g. target SDI in RO feed <3). Downstream to the pressure driven membrane process, disinfection
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could be required as a safety barrier to ensure the redundancy and the very high reliability of the water
treatment.
4.3 Filtration unit process
There are two types of membrane filtration: Pressure driven filtration and Vacuum driven filtration
(see Figure 1). In a pressure driven filtration configuration, driving force for filtration is generated by
additional pressure generated by a pump installed in the feed stream. In a vacuum driven filtration
configuration, driving force for filtration is generated by suction pump installed in the permeate stream.
There are two types of pressure driven filtration modes: cross-flow mode and dead-end mode. In a
cross-flow filtration process, most feed flow travels tangentially to the membrane surface for scouring
foulants from the membrane surface and minimizing concentration polarization. Because NF/RO
processes require high pressure due to the tightness of free-volume holes and the influence of osmotic
pressure, almost all NF/RO membranes are housed in pressure vessels and are operated under pressure
in a cross-flow orientation. In a dead-end filtration process, no cross-flow occurs, meaning that feed
flow rate equals permeate flow rate. For MF/UF, intermittent backwash with permeate and/or air is
made to recover the flux decline.
In a vacuum driven filtration process, membrane modules are immersed in an open basin, in which
feed water is introduced. In MBR, MF or UF membranes are used in a vacuum driven configuration in
an aeration tank and the driving force (i.e. pressure difference) is generated by a vacuum pump in the
permeate stream.
(a) Pressure-driven filtration
(b) Vacuum-driven filtration
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Key
A cross flow
B dead-end flow
1 feed
2 feed pump
3 permeate
4 (backwash)
5 membrane module(s)
6 concentrate
7 concentrate (recirculate)
8 recirculation pump
9 tank
10 blower
11 suction pump
Figure 1 — Typical Membrane filtration systems
4.4 Membrane filtration process design and pre- and post-shipment tests
Successful system design and constructions of membrane filtration processes for water reuse can
be achieved by appropriate membrane selections. It is important for engineers to design membrane
filtration systems after verifying the membrane specifications such as pore size, pure water permeability,
separation performance, a range of information including membrane configuration, material, operating
conditions and cleaning methods. Further details of the membrane specifications are provided
in Annex A. Before shipment, during membrane reception on site, and during commissioning, the
membrane modules/elements are typically evaluated by confirming the proper storage conditions and
whether they meet the product specifications. If required, proper storage conditions of the membrane
on site before commissioning shall be anticipated.
5 Principles and general guidelines for performance evaluation
5.1 General
The purpose of performance evaluation for membrane filtration technology is to determine whether
membrane filtration processes can consistently meet specified membrane performance requirements.
Clause 5 defines two key performance requirements in membrane performance evaluation: functional
and non-functional requirements. Performance requirements are evaluated using specified test
protocols that include sample collection methods, monitoring methods, ancillary data collection
frequency and methods, documentation and valid data analysis procedures, and their details will be
described in Clauses 6 and 7.
5.2 Functional requirements for membrane filtration process
Functional requirements for membrane filtration technology address the rejection of constituents
in the feed water to produce a highly-treated wastewater that meets the reclaimed water quality
requirements. Performance evaluation for functional requirements in membrane filtration process
are categorized (1) water quality-based performance evaluation, (2) process based performance
evaluation, and (3) integrity testing.
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5.3 Non-functional requirements for membrane filtration process
Non-functional requirements involve environmental and economic performance. Environmental
performance evaluation for membrane filtration process can be conducted with energy consumption,
chemical consumption, and volume of liquid and solid wastes. Economic performance evaluation for
membrane filtration technology can be based on LCC, which includes capital cost and operating cost.
6 Performance evaluation for functional requirement
6.1 General
Performance evaluation for water reclamation is primarily conducted through water quality analysis
of the finished (reclaimed) water to ensure the compliance for reclaimed water quality requirements
that are typically regulated at the end of water treatment trains (or at the exit of the water reclamation
plant). However, monitoring water quality at a unit process (e.g. membrane filtration) provides
additional confidence and alerts to non-compliance with the water quality requirements. It also acts as
an early warning to identify any water quality-related issues that may occur between routine samplings
of the finished water.
When a membrane is used for a long period of time, the membrane module may be damaged due to physical
defects or chemical deterioration. This can cause a deterioration in membrane separation performance
but may not be apparent in monitored water quality. Therefore, the performance evaluation based on
the water quality analysis is typically supplemented by other performance evaluation methods that
enable to monitor the membrane integrity during the system operation. These methods include direct
integrity monitoring and indirect integrity monitoring. Direct integrity monitoring is an accurate and
reliable strategy which
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