ISO 23070:2020

INTERNATIONAL ISO
STANDARD 23070
First edition
2020-12
Water Reuse in Urban Areas —
Guidelines for reclaimed water
treatment: Design principles of a
RO treatment system of municipal
wastewater
Reference number
ISO 23070:2020(E)
©
ISO 2020

---------------------- Page: 1 ----------------------
ISO 23070:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
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 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 23070:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 3
5 Application of RO treatment systems for reclaimed water . 3
5.1 Overview . 3
5.2 Design considerations. 4
5.2.1 Safety considerations . 4
5.2.2 Stability considerations . 4
5.2.3 Economy considerations . 4
5.3 RO system components . 4
5.3.1 General. 4
5.3.2 Feed water source . 5
5.3.3 Pre-treatment unit. 5
5.3.4 RO treatment unit . 5
5.3.5 Auxiliary equipment . 5
5.3.6 Post treatment unit . 5
5.3.7 Water quality and performance monitoring system . 5
6 Technical considerations of pre-treatments . 5
6.1 Quality considerations of feed water . 5
6.1.1 General water quality index . 5
6.1.2 Silt density index. 6
6.1.3 Organic index . 6
6.1.4 Biological index . 7
6.1.5 Oxidation-reduction potential. 7
6.2 Selection of mechanical pre-treatments . 7
6.2.1 Clarification . 7
6.2.2 Media/Multimedia filtration . 7
6.2.3 Activated carbon filtration. 7
6.2.4 Microfiltration and ultrafiltration . 8
6.2.5 Cartridge filtration . 8
6.3 Chemical pre-treatments . 8
6.3.1 Antiscalants . 8
6.3.2 Chemical oxidizers for disinfection of the feed . 8
6.3.3 Reductants . 8
6.3.4 Non-oxidizing biocides . 8
7 Technical and structural considerations of RO unit . 8
7.1 Components . 8
7.1.1 RO feed pumps . 8
7.1.2 RO membrane modules . 9
7.1.3 Pressure vessels. 9
7.2 Selection of RO membranes . 9
7.2.1 Membrane materials . 9
7.2.2 Membrane modules . .10
7.3 RO unit configuration .10
8 Operating conditions and maintenance system.11
8.1 Operating conditions .11
8.1.1 Pressure .11
8.1.2 Temperature .11
© ISO 2020 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 23070:2020(E)

8.1.3 Feed water flow and permeate flux .11
8.1.4 Concentrate flow .11
8.1.5 pH .12
8.2 RO performance parameters . .12
8.2.1 Permeate flow rate .12
8.2.2 Salt rejection .13
8.2.3 Pressure drop .13
8.3 Automatic chemical dosing system .13
8.3.1 Dosing point .13
8.3.2 Dosing method .13
8.4 Control and monitor system of RO performance .13
8.4.1 Instrumentation .13
8.4.2 Control system .14
8.4.3 Monitoring system.14
8.5 Cleaning system .14
8.5.1 Physical cleaning .14
8.5.2 Chemical cleaning .14
8.6 Integrity testing of RO systems .15
8.7 System failure .16
9 Post-treatment unit .17
10 RO concentrate management .17
11 Emergency response plan .17
Annex A (informative) Example of an RO treatment system for reclaimed water .19
Annex B (informative) Information of chlorine disinfection for the influent of an RO system .20
Annex C (informative) Maturity level of technologies applied to RO concentrate treatment .21
Bibliography .22
iv © ISO 2020 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 23070:2020(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. 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. 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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO's adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
This document was prepared by Technical Committee ISO/TC 282, Water reuse, Subcommittee SC 2,
Water reuse in urban areas.
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 2020 – All rights reserved v

---------------------- Page: 5 ----------------------
ISO 23070:2020(E)

Introduction
Over the past decade, with an increasing demand of high-quality reclaimed water, reverse osmosis
(RO) has been widely applied as an important option for municipal wastewater reclamation. RO is a
water purification technology that uses a semipermeable membrane to remove ions and dissolved
organic micropollutants from feed water. In reverse osmosis, an applied pressure is used to overcome
osmotic pressure, a colligative property that is driven by chemical potential differences of the solvent,
a thermodynamic parameter. The automatic operation, small footprint and consistent high permeate
quality are the advantages of an RO process, which make it widely recognized. The reclaimed water
produced by an RO system could be used as boiler replenishing water, water for industrial production
and so on.
Compared with seawater and industrial wastewater, municipal wastewater has its distinctive
features. The total dissolved solid (TDS) concentration in seawater is mainly in the range of 30,000
[1]
to 45,000 mg/l , while the TDS concentration in secondary effluent of municipal wastewater ranges
[2]
from 100 to 3,000 mg/l . Thus, the RO system of municipal wastewater could achieve higher recovery
efficiency with much lower operational pressure compared with that of seawater. However, the
dissolved organic matter (DOM) concentration in secondary effluent is in the range of 5 to 20 mg/l as
[2] [1]
dissolve organic carbon (DOC) , which is much higher than that in seawater (<2 mg/l) . Furthermore,
the components of the DOM in secondary effluent are much more complicated than those in seawater.
Long-term operation of the RO system for municipal wastewater reclamation could lead to serious
organic and biological fouling. Therefore, in order to provide the stable operation, the distinctive
features of municipal wastewater should be taken into consideration in the design of the RO unit as
well as the pre-treatment unit. The design experience of the RO system for other water sources (e.g.,
seawater and industrial wastewater) could not be applied directly to municipal wastewater.
This document provides guidelines for the planning and design of an RO treatment system for water
reuse applications in urban areas. This document is applicable to practitioners and regulatory
authorities who intend to implement principles and decisions on water reuse in a safe, reliable and
sustainable manner.
This document addresses an RO treatment system in its entirety (e.g. reclaimed water sources, pre-
treatment process, RO treatment process, post treatment process, performance of RO system, operation
and maintenance and monitoring, usage of reclaimed water).
vi © ISO 2020 – All rights reserved

---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 23070:2020(E)
Water Reuse in Urban Areas — Guidelines for reclaimed
water treatment: Design principles of a RO treatment
system of municipal wastewater
1 Scope
This document provides guidelines for the planning and design of a reverse osmosis (RO) treatment
system of municipal wastewater. This document is applicable to practitioners and authorities who
intend to implement principles and decisions on RO treatment of municipal wastewater in a safe, reliable
and sustainable manner. This document addresses RO treatment systems of municipal wastewater in
their entirety and is applicable to any RO treatment system component.
This document provides:
— standard terms and definitions;
— a description of the system components of an RO treatment system of municipal wastewater;
— design principles of an RO treatment system of municipal wastewater;
— statements on the feed water quality and technical requirements of an RO treatment system;
— guidance for operation and maintenance of an RO treatment system;
— specific aspects for consideration and emergency response.
Design parameters and regulatory values of an RO treatment system of municipal wastewater are out
of the scope of this document.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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 and definitions
For the purpose 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 https:// www .electropedia .org/
3.1
assimilable organic carbon (AOC)
organic carbon which can be used by microorganisms for assimilation
3.2
biodegradable dissolved organic carbon (BDOC)
organic carbon which can be used by microorganisms for assimilation as well as catabolism
© ISO 2020 – All rights reserved 1

---------------------- Page: 7 ----------------------
ISO 23070:2020(E)

3.3
concentrate
rejected stream exiting a membrane module under a cross-flow 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]
[SOURCE: ASTM D6161-19 , modified — Note 1 to entry added.]
3.4
feed
input solution entering the inlet of a membrane module or system
[3]
[SOURCE: ASTM D6161-19 ]
3.5
ion exchange
process by which certain anions or cations in water are replaced by other ions by passage through a
bed of ion-exchange material
[4]
[SOURCE: ISO 6107-1:2004, 46 ]
3.6
membrane rejection rate
relative measure of how much of the target constituent that was initially in the feed water is separated
from the liquid by the membrane
Note 1 to entry: Rejection is generally expressed by 1 - C2/C1, where C1 is feed concentration and C2 is permeate
concentration. To make the guideline simple, the word “membrane” is frequently omitted depending on the
context.
3.7
microfiltration
pressure driven membrane-based separation process designed to remove particles and macromolecules
in the approximate range of 0,05 to 2 μm
[3]
[SOURCE: ASTM D6161-10 ]
3.8
permeate
portion of the feed stream which passes through a membrane
[3]
[SOURCE: ASTM D6161-10 ]
3.9
pressure drop
pressure change of the influent after the treatment by an RO system
3.10
recovery rate
ratio of the permeate volume to the feed volume
3.11
reverse osmosis
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
[3]
[SOURCE: ASTM D6161-10 ]
Note 1 to entry: Reverse Osmosis (RO) removes ions based on electrochemical forces, colloids, and organics down
to 150 molecular weight. May also be called hyperfiltration.
2 © ISO 2020 – All rights reserved

---------------------- Page: 8 ----------------------
ISO 23070:2020(E)

3.12
silt density index (SDI)
index for the fouling capacity of water in reverse osmosis systems, measuring the rate at which a
[5]
0,45-micrometre filter is plugged when subjected to a constant water pressure of 206,8 kPa (30 psi)
[5]
[SOURCE: ASTM D4189-07 (2014) ]
3.13
ultrafiltration
pressure driven process employing semipermeable membrane under hydraulic pressure gradient for
the separation of components in a solution
[3]
[SOURCE: ASTM D6161-10 ]
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.
4 Abbreviated terms
AOC assimilable organic carbon
BDOC biodegradable dissolved organic carbon
BOD biochemical oxygen demand
CA cellulose acetate
COD chemical oxygen demand
DOC dissolved organic carbon
DOM dissolved organic matter
MF microfiltration
NPF normalized permeate flow
ORP oxidation-reduction potential
RO reverse osmosis
SDI silt density index
TOC total organic carbon
TSS total suspended solids
UF ultrafiltration
5 Application of RO treatment systems for reclaimed water
5.1 Overview
Over the past decade, with an increasing demand for high-quality reclaimed water, reverse osmosis (RO)
among other technologies has been widely applied as an important option for municipal wastewater
reclamation. RO technology can achieve high removal efficiency of microbes, colloidal matter, dissolved
solids, organics and inorganics from feed water. The advantages of an RO process are automatic
[6-8]
operation and high stability of RO permeate and this makes the RO process widely accepted .
© ISO 2020 – All rights reserved 3

---------------------- Page: 9 ----------------------
ISO 23070:2020(E)

5.2 Design considerations
Generally, permeate flow rate and permeate quality are used to characterize an RO treatment system
under certain feed water quality, recovery rate and operational pressure. Therefore, the main
objective of designing an RO treatment system is to meet the specific consideration of permeate
flow rate and quality with minimal operational pressure and the considerations about the costs of
system components. Furthermore, the cleaning process and maintenance should also be taken into
consideration to maintain the stable operation of the system.
5.2.1 Safety considerations
In theory, the reverse osmosis process is driven by pressure. In practice, the pressure is provided by
the feed pump of the RO process, and a pressure vessel is used to hold the membrane modules and
the pressurized feed water. Therefore, the design and operation of a nRO system shall meet the safety
consideration for a pressurized system.
5.2.2 Stability considerations
Stability represents the ability of an RO system to provide stable permeate flow rate and water quality
under certain operational conditions. In practice, because of membrane fouling, scaling or other factors
which could increase the resistance, in order to maintain a stable rate of permeate flow, the operational
pressure keeps increasing. When the operational pressure is too high, it is necessary to clean the RO
membranes. As for permeate quality, it might deteriorate because of membrane damage, membrane
degradation and membrane fouling. Therefore, the permeate quality shall be diligently monitored.
In order to enhance the stability of an RO system, provision for equalization of feed water flow prior to
the pre-treatment stage and/or the RO unit may also be considered. The resultant reduced variability
in influent flow rate would also allow for more consistent dosing of chemicals such as antiscalants,
reductants and non-oxidizing biocides.
5.2.3 Economy considerations
As for the infrastructure cost of an RO system, it is necessary to meet the considerations of permeate
flow rate and quality with a minimal cost of system components. As for the operational cost, it is
necessary to maintain the operational stability of the whole system with reasonable operational
pressure, cleaning and maintenance.
5.3 RO system components
5.3.1 General
An RO system generally consists of six essential components (see Figure 1):
— feed water source;
— pre-treatment;
— RO treatment;
— auxiliary equipment;
— post treatment (optional depending of the reclaimed water usage and quality criteria); and
— monitor.
Each part of the system should be characterized and managed with appropriate strategies. See Annex A
for the example of a typical RO treatment system for reclaimed water.
4 © ISO 2020 – All rights reserved

---------------------- Page: 10 ----------------------
ISO 23070:2020(E)

Figure 1 — The essential components of an RO treatment system for reclaimed water
5.3.2 Feed water source
Secondary or tertiary treated municipal wastewater is generally the water source to the RO process
stage of the water reclamation plant.
5.3.3 Pre-treatment unit
The pre-treatment unit may include one or more treatment stages such as physico-chemical treatment,
oxidation (e.g. ozone/AOPs), media filtration, UF/MF membrane filtration, disinfection.
5.3.4 RO treatment unit
The RO treatment unit generally includes a safety filter, a high-pressure pump
...