ISO 24416:2022

INTERNATIONAL ISO
STANDARD 24416
First edition
2022-07
Water reuse in urban areas —
Guidelines for water reuse safety
evaluation — Stability evaluation of
reclaimed water
Recyclage des eaux dans les zones urbaines — Lignes directrices
concernant l'évaluation de la sécurité du recyclage de l'eau —
Évaluation de la stabilité de l'eau réutilisée
Reference number
ISO 24416:2022(E)
© ISO 2022

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ISO 24416:2022(E)
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© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 24416:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Water quality stability .3
5.1 General . 3
5.2 E valuation principles of water quality stability . 6
6 E valuation system of water quality stability . 7
7 E valuation parameters of water quality stability . 8
7.1 General . 8
7.2 Single parameters . 8
7.3 Composite parameters . 11
7.3.1 General . 11
7.3.2 Langelier saturation index (LSI) .12
7.3.3 Ryznar stability index (RSI) . .12
7.3.4 Calcium carbonate precipitation potential (CCPP) .13
7.3.5 Aggressive index (AI) .13
7.3.6 Larson corrosion index (LR) . 13
7.3.7 Riddick corrosion index (RI) . 14
7.4 Selection principles of evaluation parameters . 15
7.5 Case study of evaluation parameters selection . 16
8 E valuation parameters of water quality stability for pipeline networks .17
9 E valuation parameters of water quality stability for equipment.17
Annex A (informative) Information on corrosion types .19
Annex B (informative) Chemical stability guidelines for water quality in urban water
supply systems of some countries .20
Annex C (informative) Guidelines for water conditioning of boiler water in Japan .21
Annex D (informative) Reuse of urban recycling water — Water quality standard for
industrial use in China .22
Annex E (informative) Water quality parameter limits of reclaimed water depending on
specific use .24
Annex F (informative) Modification methods based on the original AOC method.25
Annex G (informative) Biological stability guideline values for AOC .26
Annex H (informative) Comparison of measurement methods for evaluation parameters of
biological stability . .27
Annex I (informative) Chemical stability evaluation conclusions for different composite
parameters .28
Annex J (informative) Guideline values of reclaimed water used in toilet flushing .29
Annex K (informative) Guideline values of reclaimed water used for recreational purposes .30
Bibliography .31
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ISO 24416:2022(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 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.
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ISO 24416:2022(E)
Introduction
With economic development and population growth, the demand for water resources is steadily
increasing. Combined with the exploitation and utilization of water, numerous countries and regions
have faced water shortages to different degrees. Increasing efforts has been made to solve the water
crisis.
Water reuse has been recognized as a low-cost and effective means to alleviate water resource
shortages. Wastewater usually contains a variety of pathogens, chemical pollutants and nutrients.
Traditional water treatment cannot remove all pollutants. During the long-term utilization of reclaimed
water, residual pollutants will affect human health (e.g. potential health risks to the public and workers
handling the reclaimed water), ecological environment (e.g. pollution of receiving water, soil) and
production safety (e.g. harmful effects on equipment operation such as corrosion, scaling and fouling).
Therefore, water quality stability is a prerequisite to ensure water reuse. It is necessary to monitor
and manage the quality of reclaimed water to ensure a safe supply. Chemical stability and biological
stability are crucial aspects of water quality stability. Water quality instability usually leads to frequent
occurrences of corrosion, scaling and fouling, bacterial regrowth, increasing energy consumption and
reduced service life of relevant equipment.
There are limited guidelines or regulations specifically regarding water quality stability for urban
purposes of reclaimed water at a global level. For different types of reclaimed water applications, the
selection of stability evaluation parameters remains controversial. Stability evaluation and management
of water quality are important to ensure safe utilization of reclaimed water. It is necessary to establish
a standard for comprehensively evaluating the stability of reclaimed water.
This document aims to provide guidance on water quality stability of reclaimed water and provide
stability parameters and methods based on different needs and utilization of reclaimed water. This
document includes:
— standard terms and definitions;
— evaluation principles of water quality stability for reclaimed water;
— evaluation parameters of water quality stability for reclaimed water;
— the selection of stability evaluation parameters for pipeline networks and equipment related to
reclaimed water;
— evaluation methods of water quality stability for reclaimed water.
Critical values of evaluation parameters for water quality stability are out of the scope of this document.
The ranges of different evaluation parameters are provided for reference. The water stability control
or management involving the reclamation treatment and/or the distribution system management (e.g.
residual disinfectant) are also out of the scope of this document.
This document provides guidance on storage, transportation and application of reclaimed water. The
beneficial aspects are reduction of energy consumption, expansion of service life of equipment and
reduction of operation costs.
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INTERNATIONAL STANDARD ISO 24416:2022(E)
Water reuse in urban areas — Guidelines for water reuse
safety evaluation — Stability evaluation of reclaimed water
1 Scope
This document provides parameters and methods for water quality stability evaluation of reclaimed
water. This document can be used in various stages of water reclamation projects including storage,
transportation, application and post-assessment.
This document considers the needs and utilization of reclaimed water and is applicable to the evaluation
and management of water quality stability of reclaimed water from municipal wastewater sources,
including chemical stability and biological stability.
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 and definitions
For the purposes of this document, the terms and definitions given in ISO 20670 and the following apply.
ISO and IEC maintain terminology 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
[SOURCE: ISO 23070:2020, 3.1]
3.2
corrosion
physicochemical interaction between a metallic material and its environment that results in changes in
the properties of the metal and that can lead to significant impairment of the function of the metal, the
environment or the technical system, of which these form a part
[SOURCE: ISO 8044:2020, 3.1, modified — Note 1 to entry removed.]
3.3
critical value
boundaries of acceptable values for evaluation parameters when water quality is stable
3.4
fouling
precipitation of suspended solids, including living organisms (biofouling) and chemical substances
(inorganic or organic)
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ISO 24416:2022(E)
3.5
microbiologically influenced corrosion
MIC
corrosion (3.2) influenced by the action of microorganisms
[SOURCE: ISO 8044:2020, 4.37, modified — Note 1 to entry removed.]
3.6
scaling
crystalline scales caused by the oversaturation of chemical substances on metallic or non-metallic
surfaces
4 Abbreviated terms
AI aggressive index
AOC assimilable organic carbon
ATP adenosine triphosphate
BDOC biodegradable dissolved organic carbon
BFR biofilm formation rate
BGP bacterial growth potential
CCPP calcium carbonate precipitation potential
COD chemical oxygen demand (dichromate method)
Cr
DO dissolved oxygen
DBP disinfection by-product
ILR improved Larson corrosion index
LR Larson corrosion index
LSI Langelier saturation index
MAP microbially available phosphorus
MIC microbiologically influenced corrosion
MPN most probable number
RI Riddick corrosion index
RSI Ryznar stability index
TDS total dissolved solids
TN total nitrogen
TP total phosphorus
TSS total suspended solids
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ISO 24416:2022(E)
5 Water quality stability
5.1 General
Water quality stability is the premise of reclaimed water use. The recommended parameters for water
reuse safety in ISO 20761 include routine physical and chemical parameters, aesthetic parameters,
[1]
microbial parameters, stability parameters and toxic and harmful chemicals. Among stability
parameters, chemical stability and biological stability are important aspects.
Chemical stability includes corrosion, scaling and fouling. Corrosion can be classified into many types,
such as electrochemical corrosion, chemical corrosion, localized corrosion, pitting corrosion and layer
corrosion. Detailed information is given in Annex A. Table 1 lists factors influencing the likelihood
of corrosion. The main influencing factors include characteristics of equipment and pipelines,
characteristics of the reclaimed water and operating conditions. Reclaimed water can be used in many
fields for urban areas, such as industrial use, artificial landscape amenity, municipal non-potable
use and groundwater recharge. Related equipment includes boilers and heat exchangers, irrigation
equipment, air conditioning and toilet flushing devices. Related pipelines include steel and galvanized
steel pipelines, concrete and cement pipelines, cement-mortar-lined metal pipelines, plastic pipelines,
cast-iron and ductile-cast-iron pipelines and non-ferrous metal pipelines. Operating conditions include
temperature, flow conditions and pressure conditions. Scaling is mainly dependent on two situations.
One is the decrease in the solubility of ionic components, which lead to crystals precipitation when
thermodynamic conditions change. The other is precipitation formed by reactions between different
ionic components. Fouling is mainly caused by the precipitation of suspended chemicals. The
extent of fouling is affected by hydraulic conditions, the roughness of the contact surfaces and the
concentration, size and type of suspended chemicals.
Table 1 — Factors influencing the likelihood of corrosion
Characteristics of equipment
Characteristics of the water Operating conditions
and pipelines
— Chemical composition — Physico-chemical composition — Temperature
— Surface conditions — Colloidal and particulate matter — Flow conditions, such as flow
velocity, turbulence or laminar
— Design and construction — Living organisms
flow, continuous or intermittent
pattern
— Pressure conditions
Besides chemical stability, considering the possibility of opportunistic bacterial regrowth in reclaimed
water, biological stability is also an important aspect of water quality stability. Biological stability
includes MIC and biofouling. MIC is due to microbial activity involving bacteria, archaea and fungi.
Within bacteria, sulfate-reducing bacteria, sulfur-oxidising bacteria, iron-oxidising or reducing
bacteria, acid-producing bacteria and bacteria that excrete extra-cellular polymeric substances
significantly affect corrosion. Among these, some microbes can coexist and their cooperative
metabolisms can lead to increasing corrosion rates. Microbes can directly cause MIC by producing acids
and they can accelerate the corrosion of pre-existing agents such as O and CO by damaging mineral
2 2
passivation films on metal surfaces. Moreover, the major mechanisms of MIC include fixing anodic sites,
formation of differential aeration or chemical concentration cells and cathodic depolarisation. MIC can
cause corrosion to various materials such as carbon steel, stainless steel, aluminium alloy, magnesium,
[2]
zinc and concrete. Biofouling is caused by the excessive growth of biofilm. Biofilm is the aggregate
of microbial cells formed by microorganisms developing layers of polymer-like materials, called
extra-cellular polymeric substances, and attached at a surface-liquid interface. Microbial adhesion to
surfaces is governed by surface-charge, -free energy and -roughness. Electrostatic, hydrophobic and
chemical forces can cause microbial attachment to surfaces. Due to extra-cellular enzymes in the
biofilm, microorganisms can utilize complex organic substrates, such as humic acids that are not easily
biodegradable by microorganisms in bulk water, which enables the growth of different microorganisms
present in bulk water. Biofilm can also protect microorganisms from disinfectants and toxins in the
surrounding environment. The formation of biofilm is dependent on various environmental conditions,
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ISO 24416:2022(E)
such as salinity, temperature, conductivity, pH, DO level, BDOC and AOC content and hydrodynamic
conditions. In addition, it is not recommended that caustics are used to reduce biofilm formation in
pipeline networks, because some bacteria from biofilm can survive under unfavourable conditions
(higher pH values).
Water quality stability is affected by many factors, including physical, chemical and biological factors.
Examples of related influencing factors on water quality stability are shown in Table 2 and Table 3.
Table 2 — Examples of related influencing factors on chemical stability
Influencing factors Notes of significance
Calcium and magnesium ions determine water hardness.
Calcium and magnesium Low hardness is beneficial for passivation film formation on the inner wall of pipeline
ions networks, which can prevent further corrosion.
High hardness can lead to scale formation.
High concentration of chloride can increase conductivity of water, accelerate migration
Chloride rate of ions and electrons in the water and accelerate corrosion. More specifically, high
concentration of chloride can cause pitting corrosion, especially for stainless steel.
High concentration of sulfate can increase conductivity of water, accelerate migration
rate of ions and electrons in the water and accelerate corrosion.
Sulfate
Sulfate can easily cause scale formation when calcium ions exist.
Nitrate can greatly accelerate the general corrosion of iron in acidic solutions but has
Nitrate
[3]
slight influence on the general corrosion in neutral solutions.
When DO acts on the inner wall of pipeline networks, it can accelerate corrosion.
DO
When DO acts on the surface of formed corrosion products, it can promote passivation
films formation and prevent further corrosion.
Carbon dioxide High contents of carbon dioxide can decrease pH value and corrode metals.
Silicon dioxide Excessive silicon dioxide can form hard scales, especially for heat exchangers.
Iron can form red iron hydroxide precipitation, causing scale formation.
Iron
Water containing iron bicarbonate can also cause corrosion.
The increase of pH within specific limits (pH 7,5 to pH 9,5) can reduce the release of
pH iron. Higher pH can increase the oxidation rate of Fe(II) and formed Fe(III) can inten-
sify the physical structure of tubercles, thus inhibiting the release of internal iron.
TSS are easily disturbed by water flow and can acceleratively scour off corrosion
surface layer, thus aggravating erosion of water flow on the inner wall of pipelines.
TSS
Suspended solids are nuclei of salt crystals. Excessive suspended solids will also
promote the formation of scales.
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ISO 24416:2022(E)
Table 3 — Examples of related influencing factors on biological stability
Influencing factors Notes of significance
AOC can provide carbon and energy for heterotrophic bacteria and is generally con-
AOC
sidered a major limiting factor for the growth of heterotrophic bacteria.
BDOC is considered as the hydrolysable pool of carbon available for bacterial growth
and biofilm formation in the distribution system. The BDOC can be used to evaluate
BDOC
the reduction in chlorine demand or disinfection by-product (DBP) formation potential
through a biological process.
Due to bacterial elemental composition (e.g. molar ratio C:N:P is 100:20:1,7), nitrogen is
also required for heterotrophic growth, though in considerably smaller amounts than
organic carbon. The lack of nitrogen will limit the growth of heterotrophic bacteria.
Ammonia can be oxidized to nitrous acid by ammonia-oxidizing bacteria, which
Nitrogen simultaneously leads to pH decrease. Under low pH value, pipelines of carbon steel,
copper, aluminium and other metals are prone to corrode.
Nitrate-reducing bacteria can utilize nitrate and generate nitrogen gas which is not
corrosive, which prevents corrosion through competition with sulfate reduction by
sulfate-reducing bacteria.
Phosphorus is an important limiting factor for bacterial growth, among which phosphate
can provide nutrient source for bacteria. Compared with carbon content, phosphorus
Phosphorus
content required by bacteria is lower. The content of phosphorus in the effluent water
depends on the removal efficiency of the treatment process.
Sulfur-oxidizing bacteria can oxidize elemental sulfur and sulfide, and produce sulfate
and corrosive sulfuric acid, which can increase acidity, hydrogen penetration and
Inorganic
corrosion rates. The presence of sulfur-oxidizing bacteria can promote the growth
of sulfate-reducing bacteria by producing the products necessary for their growth
nutrients
[4]
(e.g. sulfate).
Sulfur
Sulfate-reducing bacteria can use the oxygen component of sulfate for respiration
and generate hydrogen sulfide in the absence of DO or in biofilm. The sulfide will
come out of solution at various pH ranges and then convert to sulfuric acid by sul-
fur-oxidizing bacteria, which will easily lead to corrosion in concrete sewers. Just
like sulfate-reducing bacteria, thermophilic sulfate-reducing archaea can also cause
corrosion in a similar way.
Iron-oxidizing bacteria can oxidize divalent iron Fe(II) to trivalent ion Fe(III) by using
DO and produce large amounts of iron oxide precipitates, which can alter the acidity
and promote corrosion. In biofilm, aerobic or facultative iron-oxidizing bacteria can
provide an oxygen-free local environment for sulfate-reducing bacteria growth, which
Iron [4]
can lead to more severe corrosion.
Iron-reducing bacteria can promote corrosion by altering minerals adhering to al-
loyed steel, removing passivating layers and increasing the concentration of Fe(II)
[4]
and ferrous sulfide formed by mixed communities.
The absence of DO can provide suitable conditions for anaerobic bacteria growth,
such as sulfate-reducing bacteria and iron-reducing bacteria.
Low DO levels can provide suitable conditions for facultative bacteria growth, such
as nitrate-reducing bacteria and sulfate-reducing bacteria.
High DO levels can provide suitable conditions for aerobic bacteria growth, such as
DO
ammonia-oxidizing bacteria, sulfur-oxidizing bacteria and iron-oxidizing bacteria.
High pressure and low temperature can increase DO solubility in water and prevent
anaerobic conditions in pipelines; high temperature can decrease DO levels.
The metabolism of microorganisms in biofilm can lead to concentration gradients of
DO and affect microbial community compositions.
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ISO 24416:2022(E)
Table 3 (continued)
Influencing factors Notes of significance
AOC can provide carbon and energy for heterotrophic bacteria and is generally con-
AOC
sidered a major limiting factor for the growth of heterotrophic bacteria.
BDOC is considered as the hydrolysable pool of carbon available for bacterial growth
and biofilm formation in the distribution system. The BDOC can be used to evaluate
BDOC
the reduction in chlorine demand or disinfection by-product (DBP) formation potential
through a biological process.
Increasing temperature can promote bacterial growth.
Temperature
Temperature can also affect bacterial community composition by providing compet-
itive advantages to specific bacterial species in specified temperature ranges.
Low flow can lead to low flow velocities and long retention time, providing favourable
Hydraulic
conditions for bacterial growth.
Operating conditions
High flow can lead to increasing biofilm detachment and bacterial dispersal.
conditions
Operating modes of sewers include gravity modes and pressure modes.
Under gravity modes, DO level in sewers is high and dominant microorganisms are
Pressure aerobic and facultative bacteria.
Under pressure modes, sewers are in anaerobic conditions and dominant microor-
ganisms are anaerobic bacteria.
Dissolved nutrients, extra-cellular polymeric substances, organic and inorganic nu-
Disinfectants trients adsorbed on biofilm can react with disinfectants, resulting in c
...