ISO 23056:2020

INTERNATIONAL ISO
STANDARD 23056
First edition
2020-09
Water reuse in urban areas —
Guidelines for decentralized/
onsite water reuse system — Design
principles of a decentralized/onsite
system
Réutilisation de l'eau en milieu urbain — Lignes directrices
concernant les systèmes décentralisés/sur site de réutilisation de l'eau
— Principes de conception d'un système décentralisé/sur site
Reference number
ISO 23056:2020(E)
©
ISO 2020

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ISO 23056:2020(E)

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© ISO 2020
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ISO 23056:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Planning of a decentralized/onsite water reuse system . 2
4.1 General . 2
4.2 Possible models of the system . 3
4.2.1 General. 3
4.2.2 Onsite water reuse system . 4
4.2.3 Cluster water reuse system . 5
4.2.4 Community water reuse system . 6
5 Collection of source water for decentralized/onsite water reuse .8
5.1 Source water . 8
5.2 Collection system . 8
5.3 Greywater collection, treatment and reuse . 8
6 Treatment processes . 9
6.1 General . 9
6.2 Natural treatment process .11
6.3 Aerobic, anaerobic and combined processes .12
6.4 Disinfection .12
6.5 Advanced processes .12
7 Storage and delivery system .12
8 Monitoring .13
9 Risk management and emergency response plan .13
9.1 Risk management .13
9.2 Emergency response plan .13
10 Public engagement and outreach .14
Bibliography .15
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ISO 23056:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (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 23056:2020(E)

Introduction
With economic development, climate change, rapid urbanization and increases in population, water has
become a strategic resource especially in arid and semi-arid regions. Water shortages are considered as
one of the most serious threats to the sustainable development of society. To address these shortages,
reclaimed water is increasingly being used to satisfy water demands that do not require potable water
quality. This strategy has proven useful in increasing the reliability of long-term water supplies in
many water-scarce areas. The applications of reclaimed water depending on the volumes of reclaimed
water available include restricted or unrestricted irrigation, industrial uses, toilet and urinal flushing,
firefighting and fire suppression, street cleaning, environmental and recreational uses (ornamental
water features, water bodies’ replenishment, etc.) and car washing.
While centralized water reuse facilities have been widely implemented under different ownership and
management structures, there is also a need to develop decentralized/onsite water reuse systems in
cost-effective and resource-efficient ways, which can improve flexibility and convenience. Depending on
the size and scope of the system, private and community owned systems can increase the flexibility of
the system to the needs of the owner(s). Decentralized/onsite water reuse systems have the advantage
that they can be installed for a short-term when needed and have a lower cost than centralized systems
due to sewers systems large investments. Moreover, they allow the local reuse of water and therefore
increase water productivity. Compared to centralized systems, decentralized/onsite systems still
involve local wastewater collection and treatment. They are considered to be much smaller with
fewer people connected (single, several or tens or hundreds of households) and less costly, especially
when greywater components have been separated from the blackwater for reuse. If the systems are
properly situated, designed, operated and managed, they can provide substantial environmental and
social benefits (e.g. reduction of freshwater consumption and wastewater generation) as well. The
concentrated blackwater can be treated using several treatments (e.g. septic tanks, cesspools, soil drain
fields, chemicals, bio-digesters, composting toilets and blackwater recycling systems). Decentralized/
onsite water reuse systems can also be integrated into the broader centralized systems in terms of
clustered or contracting schemes for decentralized technology with centralized operation.
The design of a decentralized/onsite water reuse system requires a thorough understanding taking
into account of scale, system components, end use requirements and other issues. This guideline can be
useful for the application of design principles as well as feasible and cost-effective approaches for safe
and reliable fit-for-purpose water reuse.
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INTERNATIONAL STANDARD ISO 23056:2020(E)
Water reuse in urban areas — Guidelines for
decentralized/onsite water reuse system — Design
principles of a decentralized/onsite system
1 Scope
This document provides guidelines for the planning, design principles and considerations of a
decentralized/onsite water reuse system and water reuse applications in urban areas.
This document is applicable to practitioners and authorities who intend to implement principles and
decisions on decentralized water reuse in a safe, reliable and sustainable manner.
This document addresses decentralized/onsite water reuse systems in their entirety and is applicable to
any water reclamation system component (e.g. source water collection, treatment, storage, distribution,
operation and maintenance and monitoring).
This document provides:
— standard terms and definitions;
— description of system components and possible models of a decentralized/onsite water reuse system;
— design principles of a decentralized/onsite water reuse system;
— common assessment criteria and related examples of water quality indicators, all without setting
any target values or thresholds;
— specific aspects for consideration and emergency response.
Design parameters and regulatory values of a decentralized/onsite water reuse system are out of the
scope of this document.
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 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/
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ISO 23056:2020(E)

3.1
cluster system
private system
decentralized water reuse system used to treat and reuse wastewater from a collection of dwellings or
facilities located adjacent to each other with typically a few owners
[SOURCE: Asano et al., 2007; CIDWT, 2009]
3.2
community system
decentralized water reuse system used to treat and reuse wastewater from a community with dwelling
units and/or high-rise buildings
Note 1 to entry: A water-tight collection system is used for transport of pre-treated effluent or raw wastewater.
[SOURCE: Asano et al., 2007; CIDWT, 2009]
3.3
onsite water reuse system
treatment unit that receives, treats and provides reclaimed water at the immediate site of wastewater
generation
[SOURCE: Asano et al., 2007]
4 Planning of a decentralized/onsite water reuse system
4.1 General
Good planning and management of a decentralized/onsite water reuse system are important. The
planning and management of a decentralized/onsite water reuse system should consider the following
aspects:
— internal planning (e.g. planning principles, targets, scope, project timeline and conceptual design);
— site selection and inspection, including population density, land availability and topography;
— wastewater quantity and quality and reuse potentials;
— scale and layout of the system and coordination and involvement in broader land use planning;
— operational and management conditions;
— operation and maintenance of residuals (e.g. sludge, screenings, trash, etc.);
— recognition and addressing of technological, economic, environmental, social and regulatory issues.
The capacity of the owner or operator to manage the system should be factored into the decision-
making process leading to the planning and selection of a system or set of systems appropriate for
the local household or community. An initial screening using criterion for safety, reliability, stability,
operability and economics is a critical element of good planning. The dynamics of the reuse system that
can be taken into consideration include system density, hydraulic and pollutant loadings, proximity to
water bodies, soil and hydrogeological conditions and the potential impacts of water quality/quantity
on groundwater and surface waters. For system reliability, it is important to conduct a risk management
approach that consider the consequences of system failures or malfunctions in terms of public health
and environmental impacts (see Table 1). In cases of high risk or non-conformance due to failures
(e.g. power or treatment processes), procedures or options can be established/built to consider use of
traditional networks, such as constructing holding or surge tanks, constructing connections to other
nearby decentralized systems or other site-specific options.
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Site investigation and assessment are important to ensure that the system is integrated into existing
and proposed urban planning which includes future development, proposed road, water or sewer line
extensions, zoning classifications, etc.
Table 1 — Considerations for risk management of a decentralized/onsite water reuse system
Potential issues Contributing factors Key risks
— Soil; Topography
— Planning (lot size)
— Environmental sensitivity
Release of contaminants due to failure
Treatment and reuse system — Flooding
of the decentralized/onsite water
and disposal area
reuse system
— Operation and maintenance
— Loading rates
— Water extraction (boreholes, wells,
springs)
— Soil type and horizon depth
Inability to renovate effluent and
— Physical characteristics
Surrounding soil prevent contaminants from reaching
— Chemical characteristics groundwater and/or surface water
— Water table depth
— Surface exposure
A considerable health risk due to expo-
— Water resources
Public health sure to contaminants and pathogens
— Aerosols
from water/ surrounding environment
— Pests (e.g. mosquitoes)
— Surface runoff
Release of contaminants into the
receiving environment (ground/
— Groundwater discharge
Environment surface waters) causing environmen-
— Flooding
tal harm (such as eutrophication) and
odour and noise considerations
— Water table
[17]
NOTE  Adapted from Carroll, et al. (2006) .
4.2 Possible models of the system
4.2.1 General
Decentralized/onsite water reuse systems come in a wide variety of options and scales. An important
aspect in considering the use of decentralized/onsite systems is the appropriate scale of implementation
to ensure proper operation and management. Onsite systems generally refer to allotment scale systems,
including onsite family/household-based systems and onsite building scale systems (e.g. urban
communities, industries, or other facilities). Decentralized systems can encompass a wider range of
scales such as a cluster system, a community system, a seasonal operation system, etc.
Traditionally, the main application of a decentralized/onsite water reuse system is for servicing
areas that are difficult to service with centralized water reuse systems due to technical or economic
considerations. There are increasing opportunities to apply decentralized systems beyond the small
town and rural communities by a mixture of different scales. Compared to centralized systems, the
planning of decentralized/onsite water reuse systems require a thorough understanding of temporal
and spatial demand variability for the end use requirements to determine an optimal design scale.
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4.2.2 Onsite water reuse system
Onsite systems typically treat wastewater close to the source, and are generally applied to serve small
to medium scale development. Figures 1 and 2 show typical examples of an onsite family/household-
based water reuse system and a building scale water reuse system respectively. Back flow preventers
should be considered as required by many jurisdictions when potable water and reclaimed water are
supplied to the same equipment (e.g. toilets, washing machines, irrigation, etc.) for safety of individual
and public systems. The maintenance and operational costs of onsite systems can be relatively high
which usually relies on additional motivation, such as limited available supply of water (drought or arid
lands) or high costs for disposal or positive environmental attitudes of individuals and households, etc.
Onsite systems for seasonally operated facilities such as seasonal hotels or campsites should be capable
of adapting to changing conditions and deal with a high variability of organic load.
Figure 1 — Typical example of an onsite family/household-based water reuse system
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NOTE Other collection and distribution systems could be used such as greywater.
Figure 2 — Typical example of an onsite building scale water reuse system
4.2.3 Cluster water reuse system
Cluster systems can be a combination of systems applied either at single onsite or communal scale
systems or both. Cluster systems offer economies and maintainability of scale, as it is more efficient
for a number of households to invest in and utilize a decentralized technology than for each household
to own and operate its own system. Additional advantages are reducing the risk for system failure and
facilitating repair. A typical example of cluster system is given in Figure 3.
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ISO 23056:2020(E)

Figure 3 — Typical example of a cluster water reuse system
4.2.4 Community water reuse system
Community systems can be serviced using alternate collection systems in conjunction with treatment
and reuse facilities. For example, wastewater solids may be retained in an onsite primary treatment
tank and then be concentrated and/or hauled to a central site for treatment. The liquid portion of the
wastewater is discharged to the collection systems and treated downstream near the point of reuse.
Other advantages of community systems compared to onsite water reuse systems are economy of scale,
the use of more sophisticated treatment processes, and the capacity to have dedicated operations and
maintenance personnel. A typical example of community system is given in Figure 4.
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Figure 4 — Typical example of a community water reuse system
Compared to centralized systems, community system ensures lower collection and distribution
cost and can offer flexible solutions to cope with the new demands wherever certain thresholds of
demographic changes are exceeded. Centralized systems can have lower operating costs per volume of
treated wastewater. Community systems can be more resilient because a failure in one system would
only affect a small part of the region. However, the overall collection and treatment is case specific.
In addition, community systems can also be integrated with a centralized system where the management
of several decentralized/onsite systems is undertaken by a single centralized entity. These systems
can reduce demands on centralized infrastructure while enabling opportunities for localized water
reuse. The same operator can manage a number of individual decentralized/onsite systems to increase
convenience for the end user, lower operator costs and may improve operations and effluent quality. A
typical example of this management concept is shown in Figure 5.
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Figure 5 — Typical example of centralized management of several decentralized and/or onsite
water reuse systems
5 Collection of source water for decentralized/onsite water reuse
5.1 Source water
The potential source water for decentralized/onsite water reuse can include wastewater, blackwater,
greywater, rainwater, etc. In most circumstances, it is expected that domestic wastewater will be used
as the source water in a decentralized/onsite water reuse system. Possible backup water resources
should also be considered, such as a potable water tie-in.
The quality of source water should meet the safety considerations for human health and environmental
safety of the reclaimed water, see ISO 20760-1. The quantity of reuse production should meet the
demand requirements. The quality of a particular water source coupled with its end uses can determine
what level of treatment is necessary.
5.2 Collection system
The collection system consists of networks with connections to the source water or septic tank effluent.
Such networks are furnished with the necessary equipment (e.g. gates, weirs, pumps) to achieve the
collection and transport function. Small scale and onsite systems may or may not include a sewer
pipeline within the site, where the collection system may include trenches, pumping stations and the
transport is usually done by carrier, see ISO 24511.
The hydraulic design of the pipe networks and connections should ensure that no backflow, or
cross connections occur. The potable water distribution system should be protected from potential
contamination from the reclaimed water piping as well as sewer, surface and rainwater drainage piping
through the use of prevention devices, labelling, marking, etc.
Pipe material should be carefully selected since leakage from collection systems may result in
groundwater or surface water contamination.
5.3 Greywater collection, treatment and reuse
Greywater excludes used water from toilets and urinals. The quality of greywater varies depending
upon the behaviour of the residents as well as the volume of water and the chemicals used. Generally, it
is less polluted and low in contaminating pathogens, nitrogen, suspended solids and turbidity compared
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ISO 23056:2020(E)

with municipal and industrial wastewaters. Special attention should be paid if wastewater from kitchen
sinks is also included as greywater source because of potential high concentration of organic loads,
fats, oil and grease.
Treatment requirements are reduced for resource recovery when wastewater streams are separated as
early as possible. The separation of greywater provides an alternative way of water reuse. Compared
with domestic wastewater reuse, greywater reuse involves smaller hygienic concerns and requires less
treatment effort. Since greywater systems are usually expensive to retrofit into an existing building,
they should be included, if possible, during planning and construction stages.
Depending on the greywater quantity, quality and the intended uses, different treatment schemes may
be applied such as physical, chemical and/or biological treatment. Common uses for greywater are
toilet flushing and irrigation.
6 Treatment processes
6.1 General
Multiple criteria analysis should be considered for the selection of a treatment scheme (e.g. life cycle
cost, health risks, environmental issues, social aspects, etc.).
Current decentralized/onsite wastewater treatment options vary widely in sophistication from simple
septic tanks to multi-stage biological treatment systems or to advanced treatment technologies. The
systems mainly consist of several or a combination of physical, chemical and biological processes such
as precipitation, adsorption, aeration, filtration, biodegradation and disinfection.
Septic tanks are widely used as onsite wastewater treatment system. Due to limited treatment
performance of septic tanks, additional treatment is usually required for reuse of septic tank effluent.
Alternatively, many enhanced treatment units are able to treat the source water directly for fit-for-
purpose water reuse.
Enhanced treatment units for decentralized/onsite water reuse can include:
a) natural treatment processes;
b) aerobic processes such as suspended growth, attached growth and combined suspended and
attached growth;
c) anaerobic processes such as anaerobic pond and anaerobic upflow filters;
d) combined (aerobic/anaerobic/natural) processes such as anaerobic-aerobic, anaerobic-natural and
anaerobic-aerobic-natural system;
e) additional polishing processes such as filtration (e.g. deep media or mechanical filtration);
f) disinfection (e.g. chlorination, ultraviolet radiation and ozonation);
g) advanced processes such as activated carbon adsorption and ion exchange, membrane filtration
(e.g. microfiltration, ultrafiltration, nanofiltration and reverse osmosis) and advanced oxidation
(e.g. electrochemical oxidation, photochemical catalytic oxidation and radiation).
Sludge handling systems (e.g. storage, thickening, dewatering, aerobic digestion and chemical
stabilization) are also important issues and should be considered.
The selection of enhanced treatment units (e.g. secondary treatment, filtration and disinfection) depend
on the reuse applications, site specific conditions, economic constraints and environmental impacts.
Typical reuse applications include garden irrigation, pond supplementation, car washing
...