Guidelines for performance evaluation of treatment technologies for water reuse systems

This document provides a performance evaluation method of treatment technology using advanced oxidation processes (AOPs) for water reuse treatment. It introduces a system of evaluating water quality to validate AOP performance through typical parameters such as the concentration of hydroxyl radicals.

Lignes directrices pour l’évaluation des performances des techniques de traitement des systèmes de réutilisation de l’eau

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Status
Published
Publication Date
21-Jun-2021
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
08-May-2021
Completion Date
07-May-2021
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INTERNATIONAL ISO
STANDARD 20468-7
First edition
2021-06
Guidelines for performance evaluation
of treatment technologies for water
reuse systems —
Part 7:
Advanced oxidation processes
technology
Lignes directrices pour l’évaluation des performances des techniques
de traitement des systèmes de réutilisation de l’eau —
Partie 7: Technologie des processus d'oxydation avancés
Reference number
ISO 20468-7:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 20468-7:2021(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 20468-7:2021(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 Abbreviated terms ............................................................................................................................................................................... 3

4 System components ........................................................................................................................................................................................... 4

4.1 Chemical source feed unit ............................................................................................................................................................. 4

4.2 UV unit ............................................................................................................................................................................................................ 4

4.3 ∙OH generation/contact unit ....................................................................................................................................................... 4

4.4 ∙OH monitoring point......................................................................................................................................................................... 4

5 Performance requirements and evaluation methods .................................................................................................... 5

5.1 Functional requirements ................................................................................................................................................................ 5

5.1.1 General...................................................................................................................................................................................... 5

5.1.2 Performance evaluation procedures .............................................................................................................. 5

5.1.3 UV transmittance ............................................................................................................................................................. 8

5.1.4 Monitoring procedure ................................................................................................................................................. 8

5.1.5 Safety requirement ........................................................................................................................................................ 8

5.2 Non-functional requirements ..................................................................................................................................................... 8

5.2.1 General...................................................................................................................................................................................... 8

5.2.2 Environmental performance ................................................................................................................................. 9

5.2.3 Economic performance .............................................................................................................................................. 9

5.2.4 Dependability performance ................................................................................................................................10

Annex A (informative) Main treatment technologies and target constituents for water reuse ...........11

Annex B (informative) Classification of AOPs...........................................................................................................................................12

Annex C (informative) Reaction formulas and feature of indicator molecules capable of

measuring ∙OH .....................................................................................................................................................................................................13

Annex D (informative) Representative ∙OH scavengers .................................................................................................................14

Bibliography .............................................................................................................................................................................................................................15

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 20468-7:2021(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.

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 20468-7:2021(E)
Introduction

Global warming and climate change have become worldwide concerns as many countries suffer from

water shortages. There has been global investment to develop alternative water resources and secure

water supplies. One of such efforts is water reclamation/reuse since it is readily available. At the

same time, the implementation of the water reuse technology raises public and regulatory concerns

on potential human health, environmental, and its social impacts. The water reclamation/reuse

technology vendors and technology users have increased needs for defining various aspects of water

reuse projects, for regulation and for international standardization. Without ISO water reuse standards,

many opportunities for sustainable development based on water reuse could be lost.

Standardization of water reuse should include objective specifications, assessments of service level and

water reuse system performance dependencies such as safety, environmental protection, resilience,

and cost-effectiveness. Therefore, appropriate methods are needed to evaluate the performance of the

reuse system.

Varying amounts of persistent organic pollutants (POPs) can be found dependent on the biological

activity of the surrounding watershed and the geochemical circulation. POPs are organic compounds

that are resistant to degradation. POPs typically are halogenated organic compounds which exhibit

high lipid solubility, thus bioaccumulate in fatty tissues. Polyhalogenated organic compounds are of

particular concern because of the stability and lipophilicity which are often correlated to their halogen

content. Since POPs accumulate and are persistent, they can adversely affect human health and the

environment as a result.

The performance of the treatment technology for water reuse should be properly evaluated in order

to select the most appropriate technology to achieve the objectives of the water reuse project. Despite

considerable research and development on therapeutic techniques, such scientific knowledge is largely

depending on the scope of commercial interests. This document establishes a specific performance

evaluation method for advanced oxidation processes (AOPs) for water reuse systems based on

ISO 20468-1 as a generic standard. To address these issues, this document provides the evaluation

of the performance of water reuse systems in many applications by providing methods that most

stakeholders can accommodate.

At the ISO TC282/SC3 meeting, a general standard for performance evaluation based on the discussion

entitled "Guidelines for Performance Evaluation of Processing Technologies for Water Reuse Systems -

Part 1: General" in ISO 20468-1 was discussed. Technology, and combinations, thereof, and descriptions

of representative technologies should be included in the individual standards submitted in accordance

with ISO 20468-1. In this context, this document establishes a specific performance evaluation method

for advanced oxidation processes (AOPs) for water reuse systems based on ISO 20468-1 as a generic

standard.

AOP technologies represent a group of treatment processes (e.g., hydrogen peroxide/ozone, hydrogen

peroxide/UV, ozone/UV, pH elevated ozonation, etc.) that rely on the production of hydroxyl radicals as

a strong oxidant capable of the complete oxidation of most organic compounds.

In water reuse systems, AOP technologies are mainly applied for disinfection and for removing total

organic carbon (TOC) including persistent organic pollutants (POPs) that are barely decomposed by

conventional oxidation processes, as indicated in Table A.1 (Annex A). For instance, direct oxidation

of chlorobenzene by ozone is known to occur very slowly; this reaction’s second-order kinetic rate

-1 -1

constant is less than 1 M s . On the other hand, the oxidation of chlorobenzene by ·OH is extremely

9 -1 -1
rapid (up to 4 X 10 M s ).

AOPs as an advanced level treatment are generally applied to tertiary treated water, as shown in

Figure 1 of ISO 20468-1.
© ISO 2021 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 20468-7:2021(E)
Guidelines for performance evaluation of treatment
technologies for water reuse systems —
Part 7:
Advanced oxidation processes technology
1 Scope

This document provides a performance evaluation method of treatment technology using advanced

oxidation processes (AOPs) for water reuse treatment. It introduces a system of evaluating water

quality to validate AOP performance through typical parameters such as the concentration of hydroxyl

radicals.
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
persistent organic pollutant (POP)

chemical substances that persist in the environment, bio-accumulate through the food web, poses a

risk of causing adverse effects to human health and the environment, and can be subject to long range

transport away from its original source

Note 1 to entry: Substances are classified as POPs according to either The Protocol to the regional UNECE

Convention on Long-Range Transboundary Air Pollution (CLRTAP) on POPs, opened for signatures in June 1998

and entered into force on 23 October 2003 or the global Stockholm Convention on POP, opened for signatures in

May 2001 and entered into force on 17 May 2004.
[1]
[SOURCE: ISO 26367-2:2017, 3.8 ]
3.1.2
advanced oxidation process (AOP)

process that generates hydroxyl radicals in sufficient quantity to remove organics by oxidation

© ISO 2021 – All rights reserved 1
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ISO 20468-7:2021(E)
3.1.2.1
hydrogen Peroxide/Ozone (H O /O )
2 2 3
combination of H O and ozone which is able to generate ·OH
2 2

Note 1 to entry: When ozone is dissolved in water, it causes a complex chain of reactions that result in the

formation of radicals including ∙OH and superoxide radicals. The addition of hydrogen peroxide to ozone also

generates ∙OH radicals. The typical stoichiometry of hydrogen peroxide and ozone based on the mass ratio is

from 0,35 to 0,45 because 0,5 moles of H O are required to every mole of O for the complete reaction of ∙OH

2 2 3
production.
3.1.2.2
hydrogen Peroxide/UV (H O /UV)
2 2

combination of H O and UV light which is able to generate ∙OH through UV photolysis of H O

2 2 2 2

Note 1 to entry: The oxidation of organics can occur by either direct photolysis or reactions with ∙OH in H O /UV

2 2
system.
3.1.2.3
ozone/UV (O /UV)

combination of ozone and UV light which is able to generate ∙OH through UV photolysis of ozone

Note 1 to entry: UV photolysis of ozone where H O is generated as an intermediate, which then decomposes

2 2
–1 –1

to ∙OH. Due to the relatively high molar extinction coefficient of ozone (ε = 3 300 M cm ), ozone/UV

254 nm
radiation can generally produce more ∙OH than H O /UV radiation.
2 2
3.1.2.4
Fenton reaction
reaction between iron(II) and hydrogen peroxide to yield ∙OH

Note 1 to entry: Fenton reaction can occur either in homogeneous systems with dissolved ferrous iron or

in heterogeneous systems in the presence of complexed iron. The by-product, ferric iron, in turn reacts with

peroxide or superoxide radical to reproduce ferrous iron. The reaction cycle of iron between the ferrous and

ferric oxidation states continuous until the H O is fully consumed, producing ∙OH in the process. As in other

2 2

AOPs, the destruction of organics is primarily due to oxidation reactions initiated by the ∙OH. Similar reactions

can occur with copper (II) in place of iron (II).
3.1.2.5
hydroxyl radical scavengers

non-target substances that react to high degree of reactivity of hydroxyl radical

Note 1 to entry: Hydroxyl radical can oxidize a broad range of organic pollutants quickly and non-selectively.

A drawback resulting from such a high degree of reactivity is that the hydroxyl radical also reacts with “non-

target” materials in solution such as chloride, nitrite, bromide, carbonate, bicarbonate, and NOM, all of which are

referred to as radical “scavengers”.
Note 2 to entry: see Annex D
3.1.2.6
UV/TiO

semiconductor photocatalysts that absorb light and involve the generation of oxidants (e.g., ∙OH and O ∙

) for the destruction of organic pollutants

Note 1 to entry: When TiO , a semiconductor photocatalyst, is illuminated by UV light (≤ 400 nm), valence band

electrons are excited to the conduction band, resulting in the production of electron and hole pairs. These

generated electron and hole pairs are capable of initiating a wide range of chemical reactions (e.g., direct

oxidation/reduction, oxidants generation). Among them, ∙OH oxidation is the primary mechanism for the

destruction of POPs. The production of ∙OH can occur via several pathways but, as with many of the other AOPs

analysed, is readily formed from hydrogen peroxide.
2 © ISO 2021 – All rights reserved
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ISO 20468-7:2021(E)
3.1.3
hydroxyl radical (∙OH)
neutral form of hydroxide ion (OH-) which possesses an unpaired electron

Note 1 to entry: The unpaired electron makes it a powerful and non-selective chemical oxidant, which acts very

rapidly with most organic compounds.
3.1.4
redox potential

potential of a reversible oxidation-reduction reaction in a given electrolyte recorded on a standard

hydrogen electrode scale
[2]
[SOURCE: ISO 8044:2020, 6.1.37 ]
3.1.5
∙OH concentration
molar concentration of ∙OH in a unit volume of liquid
3.1.6
∙OH monitor
instrument capable of measuring ∙OH concentration (3.1.5) in samples
3.1.7
electrical energy per order

electrical energy in kWh which required to degrade a contaminant by one order of magnitude in 1m of

contaminated water

Note 1 to entry: Electrical energy per order as a Figure-of-merit for AOPs has been accepted by the International

[3]
Union of Pure and Applied Chemistry (IUPAC) in 2001 .
3.1.8
UV transmittance

the fraction of photons in the UV spectrum transmitted through a material such as water or quartz. It is

preferable that an online UVT sensor be installed and used to verify UVT

Note 1 to entry: The wavelength of the UVT (unit %) should be specified, often using a path-length of 1 cm. The

measurement is calibrated compared to ultra-pure water (ISO 3696 grade 1 or equivalent).

Note 2 to entry: UVT is related to the UV absorbance (A) by the following equation (for a 1- cm path length): %

UVT = 100 × 10-A.
3.2 Abbreviated terms
AOP advanced oxidation process
E electrical energy per order
LCC life cycle cost
NOM natural organic matter
O ∙ superoxide anion radical
∙OH hydroxyl radical
OH hydroxide ion
O&M operation & maintenance
POP persistent organic pollutant
© ISO 2021 – All rights reserved 3
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ISO 20468-7:2021(E)
ROS reactive oxygen species
SCE saturated calomel electrode
TOC total organic carbon
UVT ultraviolet transmittance
4 System components

AOP technologies generally follow tertiary treatment for the purpose of attaining higher quality treated

wastewater for specific water reuse applications. AOPs involve the following two stages of oxidation: 1)

the formation of strong radical oxidants (e.g., ∙OH) and 2) the reaction of these radical oxidants with

the water contaminants. However, the term AOPs refer specifically to processes in which oxidation of

organic contaminants occurs primarily through reactions with ∙OH. The ability of an oxidant to initiate

chemical reactions can be measured in terms of its redox potential and ∙OH is one of the most reactive

oxidants in an aqueous phase with an oxidation potential of 2,8 V (pH 0) vs. NHE (normal hydrogen

electrode). In water treatment applications, AOPs usually refer to a specific subset of processes that

involve O , H O , and/or UV light. All of these processes can produce ∙OH as non-selective oxidant enable

3 2 2

to rapidly destroy a wide range of organic contaminants. Although a number of the processes noted

above may have other mechanisms for destroying organic contaminants, in general, the effectiveness of

AOPs is proportional to its ability to generate ∙OH.
Established AOP systems include two representative cases:

1) one system produces ∙OH based on the combination of chemical sources only (e.g., H O /O , etc.);

2 2 3
and

2) the other system produces ∙OH based on the combination of chemical sources and UV light (O /UV,

H O /UV, etc.)
2 2
4.1 Chemical source feed unit

The chemical source unit supplies the generation/contact unit (e.g., combinations of O , H O , UV, etc.).

3 2 2
4.2 UV unit

A UV unit has simple components including an irradiation vessel and a power control panel. UV units

may be categorized into closed and open systems, based on the configuration of UV units in the

irradiation vessel. The closed system has a UV unit, comprised of a UV lamp and its sleeve, placed in the

flow chamber. Meanwhile, the open system has a UV unit immersed in an open channel or tank.

4.3 ∙OH generation/contact unit

The ∙OH generation/contact unit typically is a unit to produce ∙OH using feeds, and directly applies the

generated ∙OH to the water, due to the high reactivity of ∙OH. The unit normally includes jet injector

for feeds or/and mechanical agitation for an even distribution of ∙OH. The ∙OH generation/contact unit

occasionally includes a UV lamp for systems employing photons (e.g., H O /UV, O /UV).

2 2 3
4.4 ∙OH monitoring point

The ∙OH monitoring unit monitors the concentration of ∙OH at the ∙OH generation/contact unit either by

ex-situ sampling and in-situ detecting.
4 © ISO 2021 – All rights reserved
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ISO 20468-7:2021(E)
5 Performance requirements and evaluation methods

The purpose of performance requirements and evaluation methods for AOP technology is to assess

whether the performance of AOP processes meets specific requirements for attaining reclaimed

water which satisfy the reclaimed water quality standards for the specific purposes of water reuse.

Performance requirements and evaluation methods include specific performance evaluation procedures

(e.g., water quality test, ∙OH quantification test, monitoring protocol), safety requirement, and

[4],[5]

environmental/energy performance as functional and non-functional requirements, respectively

5.1 Functional requirements
5.1.1 General

The design of AOPs is governed by the influent contaminant concentration, target effluent contaminant

concentration, desired flow rate, and background water quality parameters such as pH, bromide

concentration, alkalinity, etc. The key design parameters for AOPs include: chemical dosages and ratios

with other chemicals, reactor contact time, and reactor configuration. The optimum dosages, ratios, and

contact time are water-specific and treatment scenario-specific and are often determined through pilot

studies using the water matrix of interest. As can be expected, higher chemical dosages and contact

times are typically expected to result in higher removal rates; however, increasing dosages results in

higher O&M costs and possible by-product formation (e.g., bromate aldehydes, chlorate, etc.). However,

in some cases, the formation of by-products can be limited by higher chemical ratios. While AOPs have

been found to be effective for a wide variety of organic contaminants, this analysis will focus on the

practical implementation of AOPs in water reclamation, specifically for the treatment of tertiary treated

wastewaters. As previously mentioned, there are many water quality parameters that may impact the

effectiveness of any particular AOP. For example, nearly all dissolved organic compounds present in

the source water can negatively affect the removal efficiency of the target compound by consuming

∙OH. Below is a brief discussion of each of these water quality parameters and the mitigation measures

that can be taken to limit the adverse impact of these parameters on AOPs effectiveness. Regarding the

indirect parameters to judge whether AOP technology fulfills the requirements, ∙OH concentration in

the treatment system can be used.

AOPs can be divided into established and emerging technologies based on the existing literatures.

Emerging technologies are defined here as technologies that have very limited, if any, full-scale

applications for water reuse system.
Established Technologies includes:
1) Hydrogen Peroxide/Ozone (H O /O );
2 2 3
2) Ozone/UV (O /UV); and
3) Hydrogen Peroxide/UV (H O /UV)
2 2
Emerging Technologies includes:
1) Fenton Reaction; and
2) UV/TiO
5.1.2 Performance evaluation procedures

Established AOPs technologies can be divided into two cases: one is based on a coupling between

chemical oxidants and the other is based on a combination of chemical oxidants and UV light (Annex B).

CASE 1: AOPs based on the combination of chemical sources only (H O /O )
2 2 3

When O is added to water, it participates in a complex chain of reactions that result in the formation

of radicals such as the ∙OH and the O ∙ . Unlike ozone, these radical products could effectively destroy

POPs. For instance, direct oxidation of chlorobenzene by ozone is known to occur very slowly; this

© ISO 2021 – All rights reserved 5
---------------------- Page: 10 ----------------------
ISO 20468-7:2021(E)
-1 -1

reaction’s second-order kinetic rate constant is less than 1 M s . On the other hand, the oxidation

9 -1 -1

of chlorobenzene by ∙OH is extremely rapid (up to 4 X 10 M s ). The addition of hydrogen peroxide

enables the initiation of the decomposition of ozone, leading to the formation of ∙OH. . The typical

stoichiometry of hydrogen peroxide and ozone based on the mass ratio is from 0,35 to 0,45 because

0,5 moles of H O are required to every mole of O for the complete reaction of ∙OH production.

2 2 3

Two O and hydrogen peroxide contact configurations are continuously stirred basins and plug flow

reactors.

In an O unit, O is bubbled or injected through the base of the unit and allowed to diffuse through the

3 3

unit until it either escapes through the top or is completely reacted. These units are typically covered

so that excess O can be collected and directed to an off-gas decomposer. H O can be added either as a

3 2 2

single slug dose or at multiple points in the system. Automatic monitoring and control systems are used

to regulate chemical feed rates, pH, and other parameters. In addition, a variety of safety, monitoring,

and control systems are included to facilitate operation. A schematic of an H O /O system is shown in

2 2 3
Figure 1 (upper).

The major components of both a continuously stirred tank reactor and a plug flow reactor include a H O

2 2

storage tank, a H O injection system, an O generator, a liquid oxygen or oxygen from a concentrator,

2 2 3

in-line static mixers and mechanical agitation, O injector, an O contactor, an O decomposer and/or

3 3 3

off-gas recycling device, supply and discharge pumps and piping, monitoring and control systems.

CASE 2: AOPs based on the combination of chemical sources and UV light (O /UV and H O /UV)

3 2 2
A simplified schematic diagram of case 2 system is shown in Figure 1 (bottom).

For O /UV applications, O is introduced into the system at the bottom of each chamber by a stainless

3 3

steel sparger or injector. The O generator employed in the system can electrically generate O from

3 3

either air or liquid oxygen. Any O that is present in the off-gas is put through a decomposer and/or

recycling device such as activated carbon, catalyst media and heat, or combination of heat and catalyst

[6]
media .

The major components of an O /UV system include UV lamps, sleeves, and cleaning system, an O

3 3

generator and injectors, an O contactor, an O off-gas decomposer, an liquid oxygen or oxygen from a

...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 20468-7
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 7:
2021-05-07
Advanced oxidation processes
technology
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 20468-7:2021(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 20468-7:2021(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 20468-7:2021(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 Abbreviated terms ............................................................................................................................................................................... 3

4 System components ........................................................................................................................................................................................... 4

4.1 Chemical source feed unit ............................................................................................................................................................. 4

4.2 UV unit ............................................................................................................................................................................................................ 4

4.3 ∙OH generation/contact unit ....................................................................................................................................................... 4

4.4 ∙OH monitoring point......................................................................................................................................................................... 4

5 Performance requirements and evaluation methods .................................................................................................... 4

5.1 Functional requirements ................................................................................................................................................................ 5

5.1.1 General...................................................................................................................................................................................... 5

5.1.2 Performance evaluation procedures .............................................................................................................. 5

5.1.3 UV transmittance ............................................................................................................................................................. 8

5.1.4 Monitoring procedure ................................................................................................................................................. 8

5.1.5 Safety requirement ........................................................................................................................................................ 8

5.2 Non-functional requirements ..................................................................................................................................................... 8

5.2.1 General...................................................................................................................................................................................... 8

5.2.2 Environmental performance ................................................................................................................................. 9

5.2.3 Economic performance .............................................................................................................................................. 9

5.2.4 Dependability performance ................................................................................................................................10

Annex A (informative) Main treatment technologies and target constituents for water reuse ...........11

Annex B (informative) Classification of AOPs...........................................................................................................................................12

Annex C (informative) Reaction formulas and feature of indicator molecules capable of

measuring ∙OH .....................................................................................................................................................................................................13

Annex D (informative) Representative ∙OH scavengers .................................................................................................................14

Bibliography .............................................................................................................................................................................................................................15

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 20468-7:2021(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.

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.
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ISO/FDIS 20468-7:2021(E)
Introduction

Global warming and climate change have become worldwide concerns as many countries suffer from

water shortages. There has been global investment to develop alternative water resources and secure

water supplies. One of such efforts is water reclamation/reuse since it is readily available. At the

same time, the implementation of the water reuse technology raises public and regulatory concerns

on potential human health, environmental, and its social impacts. The water reclamation/reuse

technology vendors and technology users have increased needs for defining various aspects of water

reuse projects, for regulation and for international standardization. Without ISO water reuse standards,

many opportunities for sustainable development based on water reuse could be lost.

Standardization of water reuse should include objective specifications, assessments of service level and

water reuse system performance dependencies such as safety, environmental protection, resilience,

and cost-effectiveness. Therefore, appropriate methods are needed to evaluate the performance of the

reuse system.

Varying amounts of persistent organic pollutants (POPs) can be found dependent on the biological

activity of the surrounding watershed and the geochemical circulation. POPs are organic compounds

that are resistant to degradation. POPs typically are halogenated organic compounds which exhibit

high lipid solubility, thus bioaccumulate in fatty tissues. Polyhalogenated organic compounds are of

particular concern because of the stability and lipophilicity which are often correlated to their halogen

content. Since POPs accumulate and are persistent, they can adversely affect human health and the

environment as a result.

The performance of the treatment technology for water reuse should be properly evaluated in order

to select the most appropriate technology to achieve the objectives of the water reuse project. Despite

considerable research and development on therapeutic techniques, such scientific knowledge is largely

depending on the scope of commercial interests. This document establishes a specific performance

evaluation method for advanced oxidation processes (AOPs) for water reuse systems based on

ISO 20468-1 as a generic standard. To address these issues, this document provides the evaluation

of the performance of water reuse systems in many applications by providing methods that most

stakeholders can accommodate.

At the ISO TC282/SC3 meeting, a general standard for performance evaluation based on the discussion

entitled "Guidelines for Performance Evaluation of Processing Technologies for Water Reuse Systems -

Part 1: General" in ISO 20468-1 was discussed. Technology, and combinations, thereof, and descriptions

of representative technologies should be included in the individual standards submitted in accordance

with ISO 20468-1. In this context, this document establishes a specific performance evaluation method

for advanced oxidation processes (AOPs) for water reuse systems based on ISO 20468-1 as a generic

standard.

AOP technologies represent a group of treatment processes (e.g., hydrogen peroxide/ozone, hydrogen

peroxide/UV, ozone/UV, pH elevated ozonation, etc.) that rely on the production of hydroxyl radicals as

a strong oxidant capable of the complete oxidation of most organic compounds.

In water reuse systems, AOP technologies are mainly applied for disinfection and for removing total

organic carbon (TOC) including persistent organic pollutants (POPs) that are barely decomposed by

conventional oxidation processes, as indicated in Table A.1 (Annex A). For instance, direct oxidation

of chlorobenzene by ozone is known to occur very slowly; this reaction’s second-order kinetic rate

-1 -1

constant is less than 1 M s . On the other hand, the oxidation of chlorobenzene by OH is extremely

9 -1 -1
rapid (up to 4 X 10 M s ).

AOPs as an advanced level treatment are generally applied to tertiary treated water, as shown in

Figure 1 of ISO 20468-1.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 20468-7:2021(E)
Guidelines for performance evaluation of treatment
technologies for water reuse systems —
Part 7:
Advanced oxidation processes technology
1 Scope

This document provides a performance evaluation method of treatment technology using advanced

oxidation processes (AOPs) for water reuse treatment. It introduces a system of evaluating water

quality to validate AOP performance through typical parameters such as the concentration of hydroxyl

radicals.
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
persistent organic pollutant (POP)

chemical substances that persist in the environment, bio-accumulate through the food web, poses a

risk of causing adverse effects to human health and the environment, and can be subject to long range

transport away from its original source

Note 1 to entry: Substances are classified as POPs according to either The Protocol to the regional UNECE

Convention on Long-Range Transboundary Air Pollution (CLRTAP) on POPs, opened for signatures in June 1998

and entered into force on 23 October 2003 or the global Stockholm Convention on POP, opened for signatures in

May 2001 and entered into force on 17 May 2004.
[1]
[SOURCE: ISO 26367-2:2017, 3.8 ]
3.1.2
advanced oxidation process (AOP)

process that generates hydroxyl radicals in sufficient quantity to remove organics by oxidation

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ISO/FDIS 20468-7:2021(E)
3.1.2.1
hydrogen Peroxide/Ozone (H O /O )
2 2 3
combination of H O and ozone which is able to generate ∙OH radicals
2 2

Note 1 to entry: When ozone is dissolved in water, it causes a complex chain of reactions that result in the

formation of radicals including ∙OH and superoxide radicals. The addition of hydrogen peroxide to ozone also

generates ∙OH radicals. The typical stoichiometry of hydrogen peroxide and ozone based on the mass ratio is

from 0,35 to 0,45 because 0,5 moles of H O are required to every mole of O for the complete reaction of ∙OH

2 2 3
production.
3.1.2.2
hydrogen Peroxide/UV (H O /UV)
2 2

combination of H O and UV light which is able to generate ∙OH through UV photolysis of H O

2 2 2 2

Note 1 to entry: The oxidation of organics can occur by either direct photolysis or reactions with ∙OH in H O /

2 2
UV system.
3.1.2.3
ozone/UV (O /UV)

combination of ozone and UV light which is able to generate ∙OH through UV photolysis of ozone

Note 1 to entry: UV photolysis of ozone where H O is generated as an intermediate, which then decomposes

2 2
–1 –1

to ∙OH. Due to the relatively high molar extinction coefficient of ozone (ε = 3 300 M cm ), ozone/UV

254 nm
radiation can generally produce more ∙OH than H O /UV radiation.
2 2
3.1.2.4
Fenton reaction
reaction between iron(II) and hydrogen peroxide to yield ∙OH

Note 1 to entry: Fenton reaction can occur either in homogeneous systems with dissolved ferrous iron or

in heterogeneous systems in the presence of complexed iron. The by-product, ferric iron, in turn reacts with

peroxide or superoxide radical to reproduce ferrous iron. The reaction cycle of iron between the ferrous and

ferric oxidation states continuous until the H O is fully consumed, producing ∙OH in the process. As in other

2 2

AOPs, the destruction of organics is primarily due to oxidation reactions initiated by the ∙OH. Similar reactions

can occur with copper (II) in place of iron (II).
3.1.2.5
hydroxyl radical scavengers

non-target substances that react to high degree of reactivity of hydroxyl radical

Note 1 to entry: Hydroxyl radical can oxidize a broad range of organic pollutants quickly and non-selectively.

A drawback resulting from such a high degree of reactivity is that the hydroxyl radical also reacts with “non-

target” materials in solution such as chloride, nitrite, bromide, carbonate, bicarbonate, and NOM, all of which are

referred to as radical “scavengers”.
Note 2 to entry: see Annex D
3.1.2.6
UV/TiO

semiconductor photocatalysts that absorb light and involve the generation of oxidants (e.g., ∙OH and O ∙

) for the destruction of organic pollutants

Note 1 to entry: When TiO , a semiconductor photocatalyst, is illuminated by UV light (≤ 400 nm), valence band

electrons are excited to the conduction band, resulting in the production of electron and hole pairs. These

generated electron and hole pairs are capable of initiating a wide range of chemical reactions (e.g., direct

oxidation/reduction, oxidants generation). Among them, ∙OH oxidation is the primary mechanism for the

destruction of POPs. The production of ∙OH can occur via several pathways but, as with many of the other AOPs

analysed, is readily formed from hydrogen peroxide.
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ISO/FDIS 20468-7:2021(E)
3.1.3
hydroxyl radical (∙OH)
neutral form of hydroxide ion (OH-) which possesses an unpaired electron

Note 1 to entry: The unpaired electron makes it a powerful and non-selective chemical oxidant, which acts very

rapidly with most organic compounds.
3.1.4
redox potential

potential of a reversible oxidation-reduction reaction in a given electrolyte recorded on a standard

hydrogen electrode scale
[2]
[SOURCE: ISO 8044:2020, 6.1.37 ]
3.1.5
∙OH concentration
molar concentration of ∙OH in a unit volume of liquid
3.1.6
∙OH monitor
instrument capable of measuring ∙OH concentration (3.1.5) in samples
3.1.7
electrical energy per order

electrical energy in kWh which required to degrade a contaminant C by one order of magnitude in 1m

of contaminated water

Note 1 to entry: Electrical energy per order as a Figure-of-merit for AOPs has been accepted by the International

[3]
Union of Pure and Applied Chemistry (IUPAC) in 2001 .
3.1.8
UV transmittance

the fraction of photons in the UV spectrum transmitted through a material such as water or quartz. It is

preferable that an online UVT sensor be installed and used to verify UVT

Note 1 to entry: The wavelength of the UVT (unit %) should be specified, often using a path-length of 1 cm. The

measurement is calibrated compared to ultra-pure water (ISO 3696 grade 1 or equivalent).

Note 2 to entry: UVT is related to the UV absorbance (A) by the following equation (for a 1- cm path length): %

UVT = 100 × 10-A.
3.2 Abbreviated terms
AOP advanced oxidation process
E electrical energy per order
LCC life cycle cost
NOM natural organic matter
O ∙ superoxide anion radical
∙OH hydroxyl radical
OH hydroxide ion
O&M operation & maintenance
POP persistent organic pollutant
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ISO/FDIS 20468-7:2021(E)
ROS reactive oxygen species
SCE saturated calomel electrode
TOC total organic carbon
UVT ultraviolet transmittance
4 System components

AOP technologies generally follow tertiary treatment for the purpose of attaining higher quality treated

wastewater for specific water reuse applications. AOPs involve the following two stages of oxidation: 1)

the formation of strong radical oxidants (e.g., ∙OH) and 2) the reaction of these radical oxidants with

the water contaminants. However, the term AOPs refer specifically to processes in which oxidation of

organic contaminants occurs primarily through reactions with ∙OH. The ability of an oxidant to initiate

chemical reactions can be measured in terms of its redox potential and ∙OH is one of the most reactive

oxidant in an aqueous phase with an oxidation potential of 2,8 V (pH 0) vs. NHE (normal hydrogen

electrode). In water treatment applications, AOPs usually refer to a specific subset of processes that

involve O , H O , and/or UV light. All of these processes can produce ∙OH as nonselective oxidant enable

3 2 2

to rapidly destroy a wide range of organic contaminants. Although a number of the processes noted

above may have other mechanisms for destroying organic contaminants, in general, the effectiveness of

AOPs is proportional to its ability to generate ∙OH.
Established AOP systems include two representative cases:

1) one system produces ∙OH based on the combination of chemical sources only (e.g., H O /O , etc.); and

2 2 3

2) the other system produces ∙OH based on the combination of chemical sources and UV light (O /UV,

H O /UV, etc.)
2 2
4.1 Chemical source feed unit

The chemical source unit supplies the generation/contact unit (e.g., combinations of O , H O , UV, etc.).

3 2 2
4.2 UV unit

A UV unit has simple components including an irradiation vessel and a power control panel. UV units

may be categorized into closed and open systems, based on the configuration of UV units in the

irradiation vessel. The closed system has a UV unit, comprised of a UV lamp and its sleeve, placed in the

flow chamber. Meanwhile, the open system has a UV unit immersed in an open channel or tank.

4.3 ∙OH generation/contact unit

The ∙OH generation/contact unit typically is a unit to produce ∙OH using feeds, and directly applies the

generated ∙OH to the water, due to the high reactivity of ∙OH. The unit normally includes jet injector

for feeds or/and mechanical agitation for an even distribution of ∙OH. The ∙OH generation/contact unit

occasionally includes a UV lamp for systems employing photons (e.g., H O /UV, O /UV).

2 2 3
4.4 ∙OH monitoring point

The ∙OH monitoring unit monitors the concentration of ∙OH at the ∙OH generation/contact unit either by

ex-situ sampling and in-situ detecting.
5 Performance requirements and evaluation methods

The purpose of performance requirements and evaluation methods for AOP technology is to assess

whether the performance of AOP processes meets specific requirements for attaining reclaimed

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ISO/FDIS 20468-7:2021(E)

water which satisfy the reclaimed water quality standards for the specific purposes of water reuse.

Performance requirements and evaluation methods include specific performance evaluation procedures

(e.g., water quality test, ∙OH radical quantification test, monitoring protocol), safety requirement, and

[4],[5]

environmental/energy performance as functional and non-functional requirements, respectively

5.1 Functional requirements
5.1.1 General

The design of AOPs is governed by the influent contaminant concentration, target effluent contaminant

concentration, desired flow rate, and background water quality parameters such as pH, bromide

concentration, alkalinity, etc. The key design parameters for AOPs include: chemical dosages and ratios

with other chemicals, reactor contact time, and reactor configuration. The optimum dosages, ratios, and

contact time are water-specific and treatment scenario-specific and are often determined through pilot

studies using the water matrix of interest. As can be expected, higher chemical dosages and contact

times are typically expected to result in higher removal rates; however, increasing dosages results in

higher O&M costs and possible by-product formation (e.g., bromate aldehydes, chlorate, etc.). However,

in some cases, the formation of by-products can be limited by higher chemical ratios. While AOPs have

been found to be effective for a wide variety of organic contaminants, this analysis will focus on the

practical implementation of AOPs in water reclamation, specifically for the treatment of tertiary treated

wastewaters. As previously mentioned, there are many water quality parameters that may impact the

effectiveness of any particular AOP. For example, nearly all dissolved organic compounds present in

the source water can negatively affect the removal efficiency of the target compound by consuming

∙OH. Below is a brief discussion of each of these water quality parameters and the mitigation measures

that can be taken to limit the adverse impact of these parameters on AOPs effectiveness. Regarding the

indirect parameters to judge whether AOP technology fulfills the requirements, ∙OH concentration in

the treatment system can be used.

AOPs can be divided into established and emerging technologies based on the existing literatures.

Emerging technologies are defined here as technologies that have very limited, if any, full-scale

applications for water reuse system.
Established Technologies includes:
1) Hydrogen Peroxide/Ozone (H O /O );
2 2 3
2) Ozone/UV (O /UV); and
3) Hydrogen Peroxide/UV (H O /UV)
2 2
Emerging Technologies includes:
1) Fenton Reaction; and
2) UV/TiO
5.1.2 Performance evaluation procedures

Established AOPs technologies can be divided into two cases: one is based on a coupling between

chemical oxidants and the other is based on a combination of chemical oxidants and UV light (Annex B).

CASE 1: AOPs based on the combination of chemical sources only (H O /O )
2 2 3

When O is added to water, it participates in a complex chain of reactions that result in the formation

of radicals such as the ∙OH and the O ∙ . Unlike ozone, these radical products could effectively destroy

POPs. For instance, direct oxidation of chlorobenzene by ozone is known to occur very slowly; this

-1 -1

reaction’s second-order kinetic rate constant is less than 1 M s . On the other hand, the oxidation

9 -1 -1

of chlorobenzene by ∙OH is extremely rapid (up to 4 X 10 M s ). The addition of hydrogen peroxide

enables the initiation of the decomposition of ozone, leading to the formation of ∙OH. . The typical

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ISO/FDIS 20468-7:2021(E)

stoichiometry of hydrogen peroxide and ozone based on the mass ratio is from 0,35 to 0,45 because

0,5 moles of H O are required to every mole of O for the complete reaction of ∙OH production.

2 2 3

Two O and hydrogen peroxide contact configurations are continuously stirred basins and plug flow

reactors.

In an O unit, O is bubbled or injected through the base of the unit and allowed to diffuse through the

3 3

unit until it either escapes through the top or is completely reacted. These units are typically covered

so that excess O can be collected and directed to an off-gas decomposer. H O can be added either as a

3 2 2

single slug dose or at multiple points in the system. Automatic monitoring and control systems are used

to regulate chemical feed rates, pH, and other parameters. In addition, a variety of safety, monitoring,

and control systems are included to facilitate operation. A schematic of an H O /O system is shown in

2 2 3
Figure 1 (upper).

The major components of both a continuously stirred tank reactor and a plug flow reactor include a H O

2 2

storage tank, a H O injection system, an O generator, a liquid oxygen or oxygen from a concentrator,

2 2 3

in-line static mixers and mechanical agitation, O injector, an O contactor, an O decomposer and/or

3 3 3

off-gas recycling device, supply and discharge pumps and piping, monitoring and control systems.

CASE 2: AOPs based on the combination of chemical sources and UV light (O /UV and H O /UV)

3 2 2
A simplified schematic diagram of case 2 system is shown in Figure 1 (bottom).

For O /UV applications, O is introduced into the system at the bottom of each chamber by a stainless

3 3
steel sparger or injector. The O generator employed
...

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