ISO 20468-4:2021

INTERNATIONAL ISO
STANDARD 20468-4
First edition
2021-05
Guidelines for performance evaluation
of treatment technologies for water
reuse systems —
Part 4:
UV Disinfection
Lignes directrices pour l’évaluation des performances des techniques
de traitement des systèmes de réutilisation de l’eau —
Partie 4: Désinfection aux UV
Reference number
ISO 20468-4:2021(E)
©
ISO 2021

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ISO 20468-4:2021(E)

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© ISO 2021
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Published in Switzerland
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ISO 20468-4:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 List of abbreviated terms . 3
4 Purpose and function of UV disinfection . 3
4.1 Purpose . 3
4.2 Function . 3
5 System configuration . 3
5.1 General . 3
5.2 UV unit . 4
5.3 Influent water quality monitoring devices . 4
5.4 Flow meter . 4
5.5 Power control panel . 4
6 Functional requirements . 5
6.1 General . 5
6.2 Evaluation of the UV unit performance . 5
6.3 Method of monitoring UV treatment system performance . 5
6.3.1 Monitoring of influent water flow [M1] . 6
6.3.2 Quality control of influent water [M2] . 6
6.3.3 Monitoring of UV irradiation [M3] . 6
6.3.4 Monitoring of treated water quality [M4] . 7
6.4 Diagnosis of causes for system failure . 8
7 Non-Functional requirements . 8
7.1 Environmental performance . 8
7.1.1 Energy efficiency. 8
7.1.2 Chemical consumption . 8
7.2 Safety . 8
7.3 Cost effectiveness of systems — Economic evaluation by LCC. 9
7.4 Reliability and resilience . 9
Annex A (informative) Main treatment technologies and target constituents for water reuse .10
Annex B (informative) Experimental evaluation method for UV units .11
Annex C (informative) Experimental evaluation method in combination with CFD-I simulations .12
Bibliography .18
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ISO 20468-4:2021(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 282, Water reuse, Subcommittee SC 3,
Risk and performance evaluation of water reuse 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 20468-4:2021(E)

Introduction
The rapidly growing global market for water reuse technologies inevitably demands standards which
are applicable on a world-wide basis. Many regions in the world are facing water shortages, and there
is great interest in the use of technologies that can treat wastewater and make the reclaimed water
available for a wide range of reuse applications that can satisfy non-potable water demands, thereby
conserving precious potable water supplies. Simultaneously, the implementation of water reuse
schemes is raising public and regulatory concerns regarding potential human health, environmental
and societal impacts. This has led to an increasing need to specify various aspects of water reuse
projects and there is a growing need on behalf of regulators, reuse technology suppliers, and users
of those technologies for international standardization. Without ISO water reuse standards, a great
number of opportunities for sustainable development based on water reuse will be lost.
Standardization needs include objective specification and evaluation of levels of service and water
reuse system performance dependability including safety, environmental protection, resilience and
cost-effectiveness considerations. Hence, appropriate methods are needed to evaluate the performance
of treatment technologies for water reuse systems.
The performance of treatment technologies for water reuse, inter alia, should be evaluated properly
in order to select most appropriate technologies in an unbiased way to achieve the objectives of the
water reuse project. Despite considerable research and development on treatment technologies,
such scientific knowledge is largely held within commercial interests. Performance evaluations are
also useful for assessing the efficiency of existing water reuse systems and operations, including the
identification of continuous improvement opportunities. To address these challenges, this document
provides methods and tools, which can be accepted by most stakeholders, to evaluate the performance
of treatment technologies for water reuse systems from multitude of applications.
Based on the discussion in the meetings of ISO/TC 282/SC 3, ISO 20468-1 titled “Guidelines for
performance evaluation of treatment technologies for water reuse systems – Part 1: General” has
been developed to establish the standard of generic aspects for performance evaluation which can be
applied to a variety of wastewater treatment technologies and their combinations, while descriptions
specific to the representative technologies should be included in individual standards being submitted
subsequently to ISO 20468-1. In this context, this document stipulating specific ways of performance
evaluation of UV treatment technology for water reuse systems, based on ISO 20468-1 as the generic
standard is established herein.
In non-potable water reuse systems, UV technology is used mainly for disinfection as indicated in
Table A.1 and works well with secondary or tertiary treated water as shown in ISO 20468-1:2018,
Figure 1.
This guideline is intended as an integrated part of a framework for UV systems, consistent with other
items in the work of TC 282. This framework includes several important aspects such as design,
validation and verification (ISO 9000) and evaluation.
Guidelines focused on UV System Design, Validation and Evaluation are found in ISO 16075-5:2021,
Clause 7.
Guidelines focused on UV system Design, Verification and Evaluation are found in ISO 20468-4.
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INTERNATIONAL STANDARD ISO 20468-4:2021(E)
Guidelines for performance evaluation of treatment
technologies for water reuse systems —
Part 4:
UV Disinfection
1 Scope
This document provides guidelines for performance evaluation methods of UV disinfection for full scale
water reuse systems. It deals with the methods of measurement of typical parameters which indicate
performance of UV disinfection systems.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 20670, 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
biodosimetry
procedure of measuring the UV reduction equivalent dose (3.1.7) of a specific microorganism in a UV unit
and a comparing the results to the known UV dose-response curve of this microorganism determined
by bioassay (typically collimated beam methods)
3.1.2
challenge microorganism
microorganism used for a biodosimetry (3.1.1)
Note 1 to entry: Common challenge microorganisms include Bacteriophages MS2, Qβ and T1UV as well as Bacillus
subtilis spores
3.1.3
computational fluid dynamics-intensity
simulation method to model a UV unit by performing a combination of computational fluid dynamics
(CFD) and optical analysis
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3.1.4
lamp protection component
apparatus for protecting the light source, including a lamp protection sleeve, tube or other component
Note 1 to entry: Lamp protection sleeve – the quartz tube or thimble that surrounds and protects the UV lamp.
The exterior is in direct contact with the water being treated
3.1.5
low pressure lamp
-5
mercury-vapour lamp that operates at an internal pressure of 0,13 Pa to 1,3 Pa (2 × 10 psi to
-4
2 × 10 psi) and electrical input of 0,5 watts per centimetre (W/cm)
Note 1 to entry: This results in essentially monochromatic light output at 253,7 nm.
3.1.6
medium pressure lamp
mercury-vapour lamp that operate at an internal pressure of 13 kPa to 1,300 kPa (2 psi to 200 psi) and
electrical output of 50 W/cm to 300 W/cm
Note 1 to entry: This results in a polychromatic (or broad spectrum) light output at multiple wavelengths,
generally between 200 nm to 400 nm.
3.1.7
reduction equivalent dose
dose of UV in a given device which is determined by biodosimetry (3.1.1)
Note 1 to entry: See “UV dose” and “biodosimetry”.
Note 2 to entry: This UV dose is determined by measuring the inactivation of a challenge microorganism after
exposure to UV light in a UV unit and comparing the results to the known UV dose response curve of the same
challenge organism determined via Bench scale collimated beam testing.
3.1.8
UV dose
UV fluence
2
amount of UV energy given as the time integral of the fluence rate or irradiance (W/m )
2 2
Note 1 to entry: This is given in units of mJ/cm or J/m .
3.1.9
UV irradiance
UV fluence rate
UV intensity
UV output emitted from a given light source and entering a unit area of the irradiated surface. The
2 2
value is typically given in W/m or mW/cm
Note 1 to entry: The terms UV irradiance, fluence rate or intensity are often used to mean the same thing.
Note 2 to entry: For details, refer to Bolton and Linden 2003.
3.1.10
UV intensity sensor
UV irradiance (3.1.9) meter or radiometer instrument to measure UV irradiance (3.1.9)
3.1.11
UV transmittance
fraction of photons in the UV spectrum transmitted through a material such as water or quartz
Note 1 to entry: It is preferable that an online UVT sensor be installed and used to verify UVT.
Note 2 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).
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Note 3 to entry: UVT is related to the UV absorbance (A) by the following equation (for a 1- cm path length):
-A
% UVT = 100 × 10 .
3.2 List of abbreviated terms
AOPs advanced oxidation processes
BOD biochemical oxygen demand
CFD-I computational fluid dynamics-intensity
E. coli Escherichia coli
LCC life cycle cost
PCD pitch circle diameter
POPs persistent organic pollutants
RED reduction equivalent dose
TDS total dissolved solids
TSS total suspended solids
UV ultraviolet
UVT ultraviolet transmittance
4 Purpose and function of UV disinfection
4.1 Purpose
To conduct water reuse, secondary or tertiary treated wastewater requires disinfection and sometimes
further treatment by more advanced processes. The treated and disinfected wastewater is then used
for various applications such as, urban, agricultural, industrial recreational and environmental uses.
4.2 Function
UV light has been proven effective against microorganisms including bacteria, protozoa and viruses
(see Annex A). UV disinfection is achieved mostly by the absorption of photons by the genome of
microorganisms, resulting in the formation of damage such as pyrimidine dimers on DNA or RNA. Such
lesions hinder the self-replication in the microorganisms and thus deprives the infectivity. Accordingly,
UV disinfection does not require chemical addition and results in limited by-product formation.
5 System configuration
5.1 General
A UV disinfection system for water reuse can consist of the following components and systems may
have several of each component based on the disinfection application requirements.
— UV unit;
— influent water quality monitoring devices;
— flow meter;
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— power control panel.
Each component will be explained in 5.2 to 5.5.
5.2 UV unit
A UV unit has simple components including irradiation chamber, a light source, an automatic cleaning
system and a UV intensity sensor. A specific UV unit may need one or more UV intensity sensor and
one or more irradiation chamber and light source, depending on the specifics of the application. UV
units may be categorized into closed and open systems, based on the configuration of UV units in the
irradiation chamber. The closed system has a UV unit, comprised of UV lamps and their sleeves, placed
in the closed vessel flow chamber. Meanwhile, the open system has a UV unit immersed in an open
channel or chamber with gravity flow and water level control device. UV systems can also consist of
non-contact unit designs with UV lamps suspended outside a transparent conduit that carries the
wastewater.
— light source
A light source for UV disinfection should have a germicidal emission at wavelengths appropriate to
the task, often at the wavelength of 253,7 nm or a combination of wavelengths between 200-385 nm.
Options include low-pressure mercury lamps, medium-pressure mercury lamps, excimer lamps,
pulsed-Xenon lamps, and ultraviolet light emitting diodes. The light source should be housed in a lamp
protection component.
— cleaning system
A cleaning system is the device having a wiper driven by electric power supply, hydraulic power supply
or pressurized air, or ultrasonic wave, etc. Options include a mechanical wiper consisting of a brush,
ring or a mechanical chemical wiper consisting of a chamber with rings filled with a washing liquid.
— UV intensity sensor
A UV intensity sensor is installed to measure the UV irradiance in the irradiation chamber so that the
irradiance can be tracked and it can be determined whether the required dose has been provided.
— ballast
A ballast is installed when using a UV lamp as a light source. Ballasts provide the power that the lamp
converts to UV photons (energy).
5.3 Influent water quality monitoring devices
A UV transmittance monitor can be used to feed data to the system controller to adjust the power of
the lamp to assure that the required dose is provided. To check whether or not the water quality of the
influent has changed from the design conditions, water quality monitors including a UV transmittance
monitor, a turbidity meter (optional) etc. are used.
5.4 Flow meter
Generally, each UV unit should have a dedicated flow meter for several reasons, including to confirm
that the unit is operating within the validated flow rate range. The measured flow rate data may be sent
to control panel and may be utilized for light-source controlling, monitoring and operating in order to
achieve system performance. The method of flow rate measurement should be selected according to the
variability in plant flow rate and installation conditions.
5.5 Power control panel
The control panel has the following functions: power receiving, power supplying, controlling,
monitoring and operating, and other functions for the light source and other apparatuses.
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6 Functional requirements
6.1 General
Functional requirements for treatment technologies address the transformation of influent water
quality constituents to produce reclaimed water and include both water quality and water quantity
parameters.
One of the functional requirements of a given UV treatment system is to secure, at all times, enough
UV dose to obtain a target quality of the reclaimed water that is appropriate for application of such
water. The UV dose is the time integral of the fluence rate or irradiance. What is necessary to this end
includes: use of a UV light source with appropriate irradiance; and retaining the reclaimed water in a
UV irradiation chamber for a predetermined time period.
In actual equipment, the irradiation time and UV irradiance in the UV irradiation chamber vary from
one portion to another due to the shape of the chamber, as well as the location and number of the light
sources, and other similar factors. Water quality determined by, for example, suspended matter and
UV absorbing components also reduces UV transmittance, and thereby affects UV dose distribution. By
taking these influences into consideration, a predetermined UV dose, or higher dose that is sufficient
for the water flow passing through the UV irradiation chamber, shall be secured at all times.
Methods for evaluating the performance of the UV unit in the design stage and for subsequently
monitoring the performance of the UV disinfection system in operation are provided below.
6.2 Evaluation of the UV unit performance
Evaluation of the UV unit performance should be done; a number of experimental methods may be used
including those described in Annex B, while the method in Annex C is accepted as a second option.
NOTE The amount of upscaling varies from no upscaling permitted to a specific level of upscaling permitted
depending on country regulations.
Method I: Annex B (Experimental evaluation method)
I-1: Experimental testing using a challenge microorganism
I-1-1: Preliminary testing
I-1-2: Full-scale unit testing
I-2: Determine the RED

Method II: Annex C (Experimental evaluation method in combination with CFD-I simulations)
II-1: Experimental testing using a challenge organism for reference unit
II-2: Intensity measurement test on UV light source
II-3: Development of the CFD-I simulation models
II-4: Determine the RED in the unit of interest
6.3 Method of monitoring UV treatment system performance
The UV treatment system can be run automatically, so that its usual operation is generally simple
compared to other disinfection processes. What is important for routine maintenance includes:
monitoring the amount and the quality of UV treatment target water; and monitoring the UV dose.
Figure 1 shows the water flow through the UV treatment system and the monitoring points situated in
the system.
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Figure 1 — Typical configuration of UV disinfection system and monitoring points in UV
disinfection system
6.3.1 Monitoring of influent water flow [M1]
To check the water flow rate through the UV unit for deviation from the design flow rate, a flow meter
is required as ancillary equipment. To check whether the flow meter is functioning problem-free, it is
recommended to perform calibration within a period specified by the manufacturer.
EXAMPLE Manufacturer's recommendations: once a year.
6.3.2 Quality control of influent water [M2]
Colloidal solids, suspended solids, colour and dissolved solids (particularly dissolved organic
compounds) can absorb UV radiation, reduce UV transmission and decrease UV disinfection. If, in
addition, UV absorbing substances such as iron, manganese, sulphurous acid, nitrous acid, and phenol
exist, they reduce UV transmittance and thereby affect the treatment effect. Furthermore, constituents
such as iron, calcium and magnesium can cause scaling and interfere with UV irradiation and intensity.
Consequently, the presence and potential of these constituents to adversely impact disinfection shall be
addressed during the design stage and appropriate O&M cleaning procedures implemented to reduce
or eliminate their impact on disinfection.
Accordingly, these water quality parameters need to be measured and monitored on a regular basis.
If the water quality of the treatment target water does not satisfy the conditions for UV application, a
possible halt in the treatment shall be taken into consideration.
NOTE Generally, when these water quality parameters are well controlled by pre-treatment, fluctuations
are small but could be significant depending on capacity and performance of the pre-treatment.
6.3.3 Monitoring of UV irradiation [M3]
In the course of the evaluation of the UV unit, the minimum UV irradiance for a maximum flow at a
minimum UVT of the water is defined.
Monitoring UV irradiation cannot be performed by biodosimetry in routine operation and maintenance.
Instead, the UV system is operated in a way that the UV irradiance is kept within the designed range,
which is monitored by one or more online UV intensity sensors mounted on the UV irradiation chamber.
To keep the appropriate UV irradiance, the following items shall be monitored, and maintenance work
shall be conducted if necessary.
— UV light sources
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Check the cumulative use time of the UV light source. Replace the light source according to its service
life (operating time) or performance parameters presented by the manufacturer.
— Lamp protection component
When fouling substances adhere to the surface of the lamp protection component, the amount of UV that
can enter the water decreases. The extent of sleeve fouling can be monitored based on the UV intensity
sensor signal. Most UV systems have low intensity alarms that trigger when too much fouling builds
up on the lamp protection component. However, relying on the UV intensity sensor signal to assess the
extent of fouling is not always sufficient. Visually, check the degree of fouling on the surface regularly.
Make sure the UV light sources are turned off before looking at the sleeves. In addition, cleaning of the
lamp protection component should be conducted. Possible cleaning methods include physical cleaning
using automatic cleaner onlin
...