Water Reuse in Urban Areas — Guidelines for reclaimed water treatment: Design principles of a RO treatment system of municipal wastewater

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.

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Status
Published
Publication Date
08-Dec-2020
Current Stage
6060 - International Standard published
Start Date
09-Dec-2020
Completion Date
09-Dec-2020
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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
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23070
ISO/TC 282/SC 2
Water Reuse in Urban Areas —
Secretariat: SAC
Guidelines for reclaimed water
Voting begins on:
2020­08­28 treatment: Design principles of a
RO treatment system of municipal
Voting terminates on:
2020­10­23
wastewater
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 23070:2020(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 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 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
CH­1214 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/FDIS 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 consideration ......................................................................................................................................................................... 4

5.2.1 Safety consideration ..................................................................................................................................................... 4

5.2.2 Stability consideration ................................................................................................................................................ 4

5.2.3 Economy consideration ............................................................................................................................................. 4

5.3 RO system components ................................................................................................................................................................... 4

5.3.1 General...................................................................................................................................................................................... 4

5.3.2 Feed water source ........................................................................................................................................................... 5

5.3.3 Pre­treatment 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 pre­treatments ........................................................................................................................... 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 pre­treatments ............................................................................................................................................................... 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/FDIS 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 treatment .......................................................................................................................................................................17

11 Emergency response plan ........................................................................................................................................................................17

Annex A (informative) Example of a RO treatment system for reclaimed water .................................................19

Annex B (informative) Information of chlorine disinfection for the influent of a 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/FDIS 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 non­governmental, 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/FDIS 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. Reverse osmosis

(RO) is a water purification technology that uses a semipermeable membrane to remove ions and

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 a RO process, which make it widely recognized. The reclaimed water

produced by a 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 a 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 a 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).
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 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) desalination

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 a RO treatment system of municipal wastewater;

— design principles of a RO treatment system of municipal wastewater;

— statements on the feed water quality and technical requirements of a RO treatment system;

— guidance for operation and maintenance of a RO treatment system;
— specific aspects for consideration and emergency response.

Design parameters and regulatory values of a 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

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ISO/FDIS 23070:2020(E)
3.3
concentrate
rejected stream exiting a membrane module under a cross-flow mode
[3]
[SOURCE: ASTM D6161­10 ]

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.
3.4
feed
input solution entering the inlet of a membrane module or system
[3]
[SOURCE: ASTM D6161­10 ]
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 6107­1:2004, 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 D6161­10 ]
3.8
permeate
portion of the feed stream which passes through a membrane
[3]
[SOURCE: ASTM D6161­10 ]
3.9
pressure drop
pressure change of the influent after the treatment by a 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 that causes selective movement of solvent

against its osmotic pressure difference
[3]
[SOURCE: ASTM D6161­10 ]

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.
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ISO/FDIS 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 D4189­07 (2014) ]
3.13
ultrafiltration

pressure driven process employing semipermeable membrane under hydraulic pressure gradient for

the separation components in a solution
[3]
[SOURCE: ASTM D6161­10 ]

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 of 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 a RO process are automatic operation

[6­8]

and high stability of RO permeate and this makes the RO process widely accepted .

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ISO/FDIS 23070:2020(E)
5.2 Design consideration

Generally, permeate flow rate and permeate quality are used to characterize a RO treatment system

under certain feed water quality, recovery rate and operational pressure. Therefore, the main objective

of designing a 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 consideration

In theory, the reverse osmosis process is driven by pressure. In practice, the pressure is provided by

the feed pump of 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 RO system shall meet the safety

consideration for a pressurized system.
5.2.2 Stability consideration

Stability represents the ability of a 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 permeate flow rate, 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 a RO system, provision for equalization of effluent flow prior to pre-

treatment stage and or 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 consideration

As for the infrastructure cost of a 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
A RO system generally consists of six essential components:
— feed water source;
— pre-treatment;
— RO treatment;
— auxiliary equipment;

— post treatment (optional depending of the reclaimed water usage and quality criteria); and

— monitor (Figure 1).

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.
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ISO/FD
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