ISO 24575:2023
(Main)General principles and guidelines for cost analysis in planning of decentralized wastewater treatment and/or reuse
General principles and guidelines for cost analysis in planning of decentralized wastewater treatment and/or reuse
This document specifies the general principles and provides guidance on the quantitative characterization of the life cycle cost of a complete wastewater management system, including collection, treatment and, optionally, reuse. It enables the consideration of different degrees of distribution, including non-sewered systems for one or more dwellings and associated trucking operations. The methodology provided in this document is applicable to urban or rural areas wherein several decentralized wastewater treatment and reuse systems can provide a lower cost solution than a single centralized plant. Similarly, the same methodology can be applied for industrial reuse systems, where several separate plants on a large industrial site can be considered instead of one treatment system. The scope of this document includes the following: a) Guidance on the determination of the degrees of distribution of decentralized wastewater treatment and reuse systems. b) A definition of the elements and components included in the life cycle cost of the different degrees of distribution in wastewater management systems, including construction, operation and maintenance. c) Guidance on the required steps for calculating life cycle cost indicators, including considerations of term and interest, operation and maintenance, replacement parts, equipment life expectancy, the value of water for reuse and other income from by-products. d) A definition of the metrics for reporting results, including the cost per unit, scope, term and interest. The following secondary costs and other considerations are not within the scope of this document: — cost of eventual disposal of the system; — guidance on wastewater treatment process selection and design; — health and sustainability considerations (although health and sustainability are primary considerations in design and decisions); — social impact factors and/or environmental risks and impacts.
Principes généraux et lignes directrices pour l'analyse des coûts lors de la planification du traitement décentralisé et/ou de la réutilisation des eaux usées
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INTERNATIONAL ISO
STANDARD 24575
First edition
2023-05
General principles and guidelines
for cost analysis in planning of
decentralized wastewater treatment
and/or reuse
Principes généraux et lignes directrices pour l'analyse des coûts lors
de la planification du traitement décentralisé et/ou de la réutilisation
des eaux usées
Reference number
ISO 24575:2023(E)
© ISO 2023
---------------------- Page: 1 ----------------------
ISO 24575:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
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
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ISO 24575:2023(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 2
3.1 Terms and definitions . 2
3.2 Symbols and abbreviated terms . 2
4 Description of different degrees of distribution in planning and design .3
5 Generalized elements of wastewater treatment and reuse systems .4
5.1 General . 4
5.2 Collection . 4
5.3 Conveyance . 4
5.4 Treatment . 5
5.5 Effluent reuse management . 7
6 Cost items to be considered in economic life cycle analysis calculations .7
6.1 General . 7
6.2 Investment cost (C ) or CAPEX items . 7
I
6.2.1 General . 7
6.2.2 Sewer collection piping, C . 8
I,A
6.2.3 Pumping stations, C . 8
I,B
6.2.4 The treatment plant, C . 8
I,C
6.2.5 Effluent distribution piping, C . 9
I,D
6.2.6 Effluent pumping stations, C . 9
I,E
6.2.7 Treated water reservoirs, C . 9
I,F
6.3 Operating cost (C ) OPEX items . 9
O
6.3.1 General . 9
6.3.2 Electricity, C . 10
O,A
6.3.3 Labour, C . 10
O,B
6.3.4 Chemicals, C . 10
O,C
6.3.5 Sludge disposal, C . 11
O,D
6.3.6 Services, C . 11
O,E
6.3.7 Others, C . 11
O,F
6.4 Maintenance cost items (C ) . 11
M
6.5 Income or revenue: negative cost items (C ) .12
N
6.5.1 General .12
6.5.2 Income from selling treated water for reuse, I .12
w
6.5.3 Income from biogas and its products, I .12
G
6.5.4 Income from selling recovered products, I .13
S
6.5.5 Other income, I . 13
O
7 Cost calculations, factoring and results integration .14
7.1 General . 14
7.2 Conversion of all costs to present value . 14
7.3 Normalization of all costs per unit . 15
8 Reporting on results of economic life cycle analysis calculations .15
Annex A (informative) Cost calculation example .17
Annex B (informative) Correlations for CAPEX and OPEX of different process units in
a treatment plant for reuse . .19
Annex C (informative) Summary of treatment process units along with their associated
cost items .20
iii
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ISO 24575:2023(E)
Bibliography .21
iv
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ISO 24575:2023(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, in collaboration with Technical Committee ISO/TC 224 Drinking water,
wastewater and stormwater systems and services.
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.
v
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ISO 24575:2023(E)
Introduction
While energy consumption for water and wastewater treatment is significant, up to 80 % of it is used
for conveyance. This includes pumping of wastewater to the treatment facility and pumping the effluent
to its reuse site. In centralized wastewater treatment and reuse system schemes, the long-distance
conveyance through piping systems and pumping stations is also associated with capital investment,
[1],[2]
which would be hard to bear for those people living in areas of low population densities. Thus, a
network of decentralized wastewater treatment and reuse systems will potentially reduce both the
capital expenses (CAPEX) and operating expenses (OPEX) in some cases, compared with conventional
planning of centralized wastewater treatment and reuse systems. Another benefit of decentralized
[3],[4]
treatment is enabling local reuse, mainly for irrigation.
Distributed design is the concept of providing several decentralized wastewater treatment systems
instead of one central plant, as outlined in other International Standards, such as ISO 23056, which
defines and describes different degrees of decentralization of wastewater treatment plants and
discusses considerations that should be taken in the selection of each alternative. Due to development
in automation and telecommunication, as well as in biological wastewater treatment processes, the
distributed design concept has become a viable option. Potential savings in using distributed design
include:
— lower collection and pumping system construction costs;
— lower collection and pumping system operation and maintenance costs;
— lower energy consumption for pumping;
— local availability for reuse in agriculture or industry or landscape irrigation.
However, potential drawbacks include:
— higher specific cost of each plant compared with a centralized wastewater treatment and reuse
system;
— higher operator attention required for many plants compared with one plant.
This document aims to provide guidelines for life cycle cost assessment for any degree of distribution in
the planning of a network of decentralized wastewater treatment and reuse systems in order to enable
the cost optimization of the design.
vi
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INTERNATIONAL STANDARD ISO 24575:2023(E)
General principles and guidelines for cost analysis in
planning of decentralized wastewater treatment and/or
reuse
1 Scope
This document specifies the general principles and provides guidance on the quantitative
characterization of the life cycle cost of a complete wastewater management system, including collection,
treatment and, optionally, reuse. It enables the consideration of different degrees of distribution,
including non-sewered systems for one or more dwellings and associated trucking operations.
The methodology provided in this document is applicable to urban or rural areas wherein several
decentralized wastewater treatment and reuse systems can provide a lower cost solution than a single
centralized plant. Similarly, the same methodology can be applied for industrial reuse systems, where
several separate plants on a large industrial site can be considered instead of one treatment system.
The scope of this document includes the following:
a) Guidance on the determination of the degrees of distribution of decentralized wastewater
treatment and reuse systems.
b) A definition of the elements and components included in the life cycle cost of the different degrees
of distribution in wastewater management systems, including construction, operation and
maintenance.
c) Guidance on the required steps for calculating life cycle cost indicators, including considerations of
term and interest, operation and maintenance, replacement parts, equipment life expectancy, the
value of water for reuse and other income from by-products.
d) A definition of the metrics for reporting results, including the cost per unit, scope, term and interest.
The following secondary costs and other considerations are not within the scope of this document:
— cost of eventual disposal of the system;
— guidance on wastewater treatment process selection and design;
— health and sustainability considerations (although health and sustainability are primary
considerations in design and decisions);
— social impact factors and/or environmental risks and impacts.
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
1
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ISO 24575:2023(E)
3 Terms, definitions, symbols and abbreviated terms
3.1 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/
3.1.1
distributed system
two or more treatment plants in different geographical locations linked to a central system, either
physically or by management
[6]
Note 1 to entry: See WEF Fact Sheet “Distributed Systems Overview” (ref. WSEC-2019-FS-012).
3.1.2
degree of distribution
number of treatment plants to treat a certain population
Note 1 to entry: A high degree of distribution means many plants to treat the population, while a low degree of
distribution means a number as low as one centralized plant to treat that same population.
3.1.3
non-sewered system
NSS
system that is not connected to a networked sewer and collects, conveys and fully treats the specific
input to allow for safe reuse or disposal of the generated solid output and/or effluent
Note 1 to entry: A non-sewered system is also referred to as an “on-site treatment system”, see ISO 24513:2019,
3.5.16.
[SOURCE: ISO 30500:2018, 3.1.1.1, modified — Note to entry replaced.]
3.1.4
total installed cost
final cost of designing, fabricating and building a capital project or industrial asset
Note 1 to entry: The total installed cost includes the cost of labour and materials.
3.2 Symbols and abbreviated terms
AOP advanced oxidation processes
C investment cost
I
C maintenance cost
M
C negative cost
N
C operating cost
O
CAPEX capital expenses
IFAS integrated fixed-film activated sludge
MABR membrane aerated biofilm reactor
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ISO 24575:2023(E)
MBBR moving bed bio reactor
MBR membrane bio reactor
NPV net present value
OPEX operating expenses
PE population equivalent
PV present value
RO reverse osmosis
SBR sequencing batch reactor
UASB upflow anaerobic sludge blanket
UV ultraviolet (irradiation, in context of disinfection)
WRRF water resource recovery facility
4 Description of different degrees of distribution in planning and design
The difference between decentralized wastewater treatment systems (3.1.1) and distributed
wastewater treatment systems (see ISO 20670) is that distributed systems are located in different
geographical locations but are linked to a central system either physically or by management, whereas
decentralized systems can be located in a different geographical location but are not linked physically
or are not managed under the umbrella of a centralized system.
The degree of distribution (3.1.2), meaning the number of treatment units for a given population, can be
as high as one system for each household (on-site systems) or as low as one single treatment plant for
a city, town or village (centralized system), or many degrees in between, such as one system per street
or one system for every cluster of households or drainage basin. The collection of wastewater can be
via a piped network (a sewer system) or by motorized vehicles, such as vacuum trucks, in non-sewered
systems. Determining the required number of systems can be challenging in the design of a wastewater
treatment and reuse plan. In some cases, the means to meet this challenge can be through an economic
estimation of the long-term cost.
A single large plant may benefit from the economy of scale of its equipment and from lower operation
and maintenance costs compared with a distributed system made up of multiple decentralized systems.
However, distributed systems can offset much of this benefit through lower CAPEX for piping and
pumping as well as lower OPEX for pumping energy, on both wastewater and water for reuse. Therefore,
the overall cost benefit of a distributed design or a centralized design changes from one place to another
and should be calculated in order to make a decision based on costs.
A structured analysis of the total cost per unit of wastewater treatment for reuse was demonstrated
by multiple computerized simulations for different types of terrain and different population densities.
[9]
The results show that for the lowest population density found in rural areas, the highest degree
of distribution is associated with the lowest cost in flat, hilly or mountainous terrains, whereas in
suburban areas it greatly depends upon the terrain. A less distributed design results in a lower cost in
flat terrain, whereas a more distributed design results in a lower cost in mountainous terrain.
[10]
An example of two different degrees of distribution for a specific case is given by van Afferden et al.,
showing a distributed scenario of nine decentralized systems (indicated there by white triangles with
a dark frame) and just one pumping station, all managed by one utility. For comparison, a centralized
scenario with one wastewater treatment plant is shown (indicated there by a single dark triangle),
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ISO 24575:2023(E)
supported by six pumping stations (indicated there by bright rectangles connected to dashed lines) and
several kilometres of a trunk pipe.
NOTE There are cases in small rural communities in which the communal decentralized wastewater
treatment and reuse systems are not equipped to treat sludge. In such cases, the sludge generated in these
facilities is collected and brought to centralized wastewater treatment plants for treatment.
5 Generalized elements of wastewater treatment and reuse systems
5.1 General
In the planning of wastewater management systems for reuse or other purposes, there are many
components and subsystems to be selected and designed, as listed in 5.2 to 5.5. All costs associated
with all these elements of the system should be included in the cost comparison of different degrees of
distribution of the entire plan.
The following subsections provide context, along with a brief explanation of the nature and scope of
each of these elements.
5.2 Collection
The collection system is roughly divided into stages from the source towards its final destination, as
[11]
shown in available publications. For the purposes of this document, the following notation will be
followed in order of flow, from each home in a lateral sewer up to the intercepting sewer or pressure
[12]
main that reaches the wastewater treatment plant (based on EPA notation ): a) lateral sewer;
b) branch sewer; c) trunk sewer (main sewer); d) intercepting sewer; e) pressure main.
Systems may have all or part of these collection system components for different degrees of distribution.
For example, an on-site treatment system will typically only have a lateral sewer collecting from the
dwelling to the treatment system.
Trucking or hauling of wastewater or sludge is sometimes an alternative to collection and conveyance
systems, especially in non-sewered systems or on-site treatment systems. When any part of the
wastewater is disposed of by trucking or hauling, it is accounted for as an operational cost instead of an
investment cost.
5.3 Conveyance
Pumping stations and lift stations are used whenever wastewater conveyance by gravity is not possible,
either as an intermediate or final run of part of the collection system. Different designs are common for
[13], [14]
a sewage pumping or lift station, with the following typical main components:
a) screening to protect the pumps from clogging;
b) a pit or a well to intercept the sewage and provide an operational volume and buffering;
c) pumps, including redundancy;
d) discharge pressure piping;
e) venting and optional means for odour control.
Vacuum collection systems are a recent alternative to gravity collection systems when the latter are
not practicable due to area limitation. The vacuum collection sewers use suction (negative pressure) to
[15], [16]
move the sewage through the following three main stages:
— Vacuum valve pit: sewage collection from individual households or homes by gravity. Once the pit is
full, a valve is opened and atmospheric pressure forces the wastewater to the vacuum branches.
4
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ISO 24575:2023(E)
— Vacuum mains: a network of vacuum piping collecting sewage from the collection chambers of
individual housings and gradually converging towards the vacuum station. The pressure difference
between the valve pit and the vacuum station pulls the wastewater through the vacuum mains.
— Vacuum station: producing the suction for the vacuum piping network connected to it and typically
pumping the sewer to the wastewater treatment plant.
It is reiterated that trucking or hauling of wastewater or sludge is sometimes an alternative to collection
and conveyance systems, especially in non-sewered systems or on-site treatment systems. When any
part of the wastewater is disposed of by trucking or hauling, it is accounted for as an operating cost
instead of an investment cost.
5.4 Treatment
The treatment plant, also referred to as a WRRF, includes all installed water treatment processes used
to achieve compliance with local discharge standards or reuse requirements. These typically include
[17]
the process sub-sections or categories described as follows and summarized in Table C.1.
In cases where different effluent requirements are applicable for different plant sizes, such as between
a decentralized plant and a centralized plant, each plant or plan may be made with the requirements
for its type, as would be the eventual design for regulatory approval. For example, in some places, small
wastewater treatment and reuse systems are not required to perform tertiary treatment for reuse
in irrigation of tree-grown crops, whereas a large plant is required to perform tertiary treatment
regardless. In such cases, the cost of tertiary treatment does not have to be included where it is not
needed.
a) Pre-treatment: physical processes to remove elements that could damage downstream equipment
and also remove easily removable constituents to improve downstream process efficiency. Usually,
pre-treatment units are designed to handle diurnal and seasonal flow variations.
The costing of pre-treatment shall include any aeration, mixing, chemicals, sludge treatment and
disposal, whether constant, periodic or occasional over the costing period. The pre-treatment
process contains some or all of the following main units:
— Screening: removal of large particulate matter and objects that can usually be disposed of as
trash. There are manual or mechanical screens and the screens openings can be coarse or fine.
Screening is often installed in two stages, with a coarse screen followed by a fine screen.
— Grit and grease removal unit: removes sand and gravel as well as fat, oil and grease.
— Equalization tank: equalizes flowrates and organic loads in order to reduce the size and cost of
downstream units and to achieve constant loads on the process units. It should be considered
that smaller sewer systems have a higher ratio of peak flow to average flow than larger systems.
b) Primary treatment: partial removal of suspended solids by gravity in a sedimentation tank or
pond. The quantity of sludge discharged from this operation shall be included in sludge treatment
cost calculations. If chemicals are added to the primary treatment, their cost shall be included in
the plant operating cost.
c) Secondary treatment: a biological treatment process, including separation between solids and
liquids, such as a secondary clarifier or membrane separation. Such processes are typically based
on suspended biomass, such as the activated sludge process, SBR or MBR, a biofilm process or a
combination of both, such as MBBR, IFAS, MABR or trickling filters. The process can be intensive, as
in the examples mentioned, or an extensive process, such as constructe
...
2022-12-11
ISO/FDIS 24575:2022(E)
ISO/TC 282/SC 2/JWG 1
Secretariat: SAC
GuidelinesDate: 2023-02-14
General principles and guidelines for cost analysis in planning of
decentralized wastewater treatment and/or reuse
FDIS stage
© ISO 2023 – All rights reserved
---------------------- Page: 1 ----------------------
ISO/FDIS 24575:2023(E)
© ISO 2022 2023
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
Fax: +41 22 749 09 47
EmailE-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2023 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 24575:2023(E)
Contents
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Symbols and abbreviated terms . 2
4 Description of different degrees of distribution in planning and design . 3
5 Generalized elements of wastewater treatment and reuse systems . 4
5.1 General . 4
5.2 Collection . 4
5.3 Conveyance . 4
5.4 Treatment. 5
5.5 Effluent reuse management . 7
6 Cost items to be considered in economic life cycle analysis calculations . 7
6.1 General . 7
6.2 Investment cost (C ) or CAPEX items . 7
I
6.2.1 General . 7
6.2.2 Sewer collection piping, C . 8
I,A
6.2.3 Pumping stations, C . 8
I,B
6.2.4 The treatment plant, C . 8
I,C
6.2.5 Effluent distribution piping, C . 8
I,D
6.2.6 Effluent pumping stations, C . 9
I,E
6.2.7 Treated water reservoirs, C . 9
I,F
6.3 Operating cost (C ) OPEX items . 9
O
6.3.1 General . 9
6.3.2 Electricity, C . 9
O,A
6.3.3 Labour, C . 10
O,B
6.3.4 Chemicals, C . 10
O,C
6.3.5 Sludge disposal, C . 11
O,D
6.3.6 Services, C . 11
O,E
6.3.7 Others, C . 11
O,F
6.4 Maintenance cost items (C ) . 11
M
6.5 Income or revenue: negative cost items (C ) . 12
N
6.5.1 General . 12
6.5.2 Income from selling treated water for reuse, I . 12
w
6.5.3 Income from biogas and its products, I . 12
G
6.5.4 Income from selling recovered products, I . 13
S
6.5.5 Other income, I . 13
O
7 Cost calculations, factoring and results integration . 14
7.1 General . 14
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ISO/FDIS 24575:2023(E)
7.2 Conversion of all costs to present value . 14
7.3 Normalization of all costs per unit . 15
8 Reporting on results of economic life cycle analysis calculations . 16
Annex A (informative) Cost calculation example . 17
Annex B (informative) Correlations for CAPEX and OPEX of different process units in a treatment plant
for reuse . 20
Annex C (informative) Summary of treatment process units along with their associated cost items . 21
Bibliography . 22
iv © ISO 2023 – All rights reserved
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ISO/FDIS 24575:2023(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, in collaboration with Technical committeeCommittee ISO/TC 224 Drinking
water, wastewater and stormwater systems and services.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2023 – All rights reserved v
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ISO/FDIS 24575:2023(E)
Introduction
While energy consumption for water and wastewater treatment is significant, up to 80 % of it is used for
conveyance. This includes pumping of wastewater to the treatment facility and pumping the effluent to
its reuse site. In centralized wastewater treatment and reuse system schemes, the long-distance
conveyance through piping systems and pumping stations is also associated with capital investment,
[1],[2[1],[2] ]
which would be hard to bear for thethose people living in areas of low population densities. . Thus,
a network of decentralized wastewater treatment and reuse systems will potentially reduce both the
capital expenses (CAPEX) and operating expenses (OPEX) in some cases, compared with conventional
planning of centralized wastewater treatment and reuse systems. Another benefit of decentralized
[3],[4[3],[4] ]
treatment is enabling local reuse, mainly for irrigation. .
Distributed design is the concept of providing several decentralized wastewater treatment systems
[5]
instead of one central plant, as outlined in other International Standards, such as ISO 23056:2020 ,,
which defines and describes different degrees of decentralization of wastewater treatment plants and
discusses considerations that should be taken in the selection of each alternative. Due to development in
automation and telecommunication, as well as in biological wastewater treatment processes, the
distributed design concept has become a viable option. Potential savings in using distributed design
include:
— — lower collection and pumping systemssystem construction costs;
— — lower collection and pumping system operation and maintenance costs;
— — lower energy consumption for pumping;
— — local availability for reuse in agriculture or industry or landscape irrigation.
However, potential drawbacks include:
— — higher specific cost of each plant compared with a centralized wastewater treatment and reuse
system;
— — higher operator attention required for many plants compared with one plant.
This document aims to provide guidelines for life cycle cost assessment for any degree of distribution in
the planning of a network of decentralized wastewater treatment and reuse systems in order to enable
the cost optimization of the design.
vi © ISO 2023 – All rights reserved
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ISO/FDIS 24575:2023(E)
GuidelinesGeneral principles and guidelines for cost analysis in
planning of decentralized wastewater treatment and/or reuse
1 Scope
This document specifies the general principles and provides guidance on the quantitative
characterization of the life cycle cost of a complete wastewater management system, including collection,
treatment and, optionally, reuse. It enableenables the consideration of different degrees of distribution,
including non-sewered systems for one or more dwellings and associated trucking operations.
The methodology provided in this document is applicable to urban or rural areas wherein several
decentralized wastewater treatment and reuse systems maycan provide a lower cost solution than a
single centralized plant. Similarly, the same methodology can be applied for industrial reuse systems,
where several separate plants on a large industrial site can be considered instead of one treatment
system.
The scope of this document includes the following:
a) a) Guidance on the determination of the degrees of distribution of decentralized wastewater
treatment and reuse systems.
b) b) A definition of the elements and components included in the life cycle cost of the different degrees
of distribution in wastewater management systems, including construction, operation, and
maintenance.
c) c) Guidance on the required steps for calculating life cycle cost indicators, including considerations
of term and interest, operation and maintenance, replacement parts, equipment life expectancy, the
value of water for reuse and other income from by-products.
d) d) DefinitionA definition of the metrics for reporting results, including the cost per unit, scope, term
and interest.
The following secondary costs and other considerations are not within the scope of this document:
— — cost of eventual disposal of the system;
— — guidance on wastewater treatment process selection and design;
— — health and sustainability considerations (although health and sustainability are primary
considerations in design and decisions);
— — social impact factors and/or the environmental risks and impacts.
42 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
53 Terms, definitions, symbols and abbreviated terms
5.13.1 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
© ISO 2023 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO/FDIS 24575:2023(E)
— — IEC Electropedia: available at https://www.electropedia.org/
3.1.1
distributed system
distributed systems are two or more treatment plants in different geographical locations, linked to a
central system, either physically, or by management
[6 [6] ]
Note 1 to entry: See WEF Fact Sheet “Distributed Systems Overview” (ref. WSEC-2019-FS-012). ) .
3.1.2
degree of distribution
number of treatment plants to treat a certain population
Note 1 to entry: A high degree of distribution means many plants to treat the population, while a low degree of
distribution means a number as low as one centralized plant to treat that same population.
3.1.3
non-sewered system
NSS
system that is not connected to a networked sewer and collects, conveys and fully treats the specific input
to allow for safe reuse or disposal of the generated solid output and/or effluent
Note 1 to entry: A non-sewered system is also referred to as an “onsiteon-site treatment system”, see
[7]
ISO 24513:2019, 3.5.16. .
[8]
[SOURCE: ISO 30500:2018, 3.1.1.1, modified — Note to entry replaced.] .]
3.1.4
total installed cost
final cost of designing, fabricating and building a capital project or industrial asset
Note 1 to entry: The total installed cost includes the cost of labour and materials.
3.1.5
TNPV
total net present value
3.2 sum of the present value of all operating expense (Symbols and abbreviated terms
OPEX) items and the total investment cost (C )
I
5.5 Abbreviated terms
AOP advanced oxidation processes
CAPEX capital expenses
OPEX operating expenses
C investment cost
I
C operating cost
O
C maintenance cost
M
C negative cost
N
C operating cost
O
CAPEX capital expenses
IFAS integrated fixed-film activated sludge
MABR membrane aerated biofilm reactor
MBBR moving bed bio reactor
2 © ISO 2023 – All rights reserved
---------------------- Page: 8 ----------------------
ISO/FDIS 24575:2023(E)
MBR membrane bio reactor
MABR membrane aerated biofilm reactor
NPV net present value
OPEXPV Present valueoperating expenses
PE population equivalent
PV present value
RO reverse osmosis
SBR sequencing batch reactor
UASB upflow anaerobic sludge blanket
UV ultraviolet (irradiation, in context of disinfection)
WRRF water resource recovery facility
64 Description of different degrees of distribution in planning and design
The difference between decentralized wastewater treatment systems (3.1.1(3.1.1)) and distributed
wastewater treatment systems (see ISO 20670) is that distributed systems are located in different
geographical locations but are linked to a central system either physically or by management, whereas
decentralized systems can be located in a different geographical location but are not linked physically or
are not managed under the umbrella of a centralized system.
The degree of distribution (3.1.2(3.1.2),), meaning the number of treatment units for a given population,
can be as high as one system for each household (onsiteon-site systems) or as low as one single treatment
plant for a city, town or village (centralized system), or many degrees in between, such as one system per
street or one system for every cluster of households or drainage basin. The collection of wastewater can
be via a piped network (a sewer system) or by motorized vehicles, such as vacuum trucks, in non-sewered
systems. Determining the required number of systems can be challenging in the design of a wastewater
treatment and reuse plan. In some cases, the means to meet this challenge can be through an economic
estimation of the long-term cost.
A single large plant may benefit from the economy of scale of its equipment and from lower operation
and maintenance costs compared towith a distributed system made up of multiple decentralized systems.
However, distributed systems can offset much of this benefit through lower CAPEX for piping and
pumping as well as lower OPEX for pumping energy, on both wastewater and water for reuse. Therefore,
the overall cost benefit of a distributed design or a centralized design changes from one place to another
and should be calculated in order to make a decision based on costs.
A structured analysis of the total cost per unit of wastewater treatment for reuse was demonstrated by
[9[9] ]
multiple computerized simulations for different types of terrain and different population densities. .
The results show that for the lowest population density found in rural areas, the highest degree of
distribution is associated with the lowest cost in flat, hilly or mountainous terrains, whereas in suburban
areas it greatly dependeddepends upon the terrain: a. A less distributed design resultedresults in a lower
cost in flat terrain, whereas a more distributed design resulted isresults in a lower cost in mountainous
terrain.
[10
An example of two different degrees of distribution for a specific case is given by van Afferden et al., ,
[10] ]
2015 showing a distributed scenario of nine decentralized systems (indicated there by white triangles
with a dark frame) and just one pumping station, all managed by one utility. For comparison, a centralized
scenario with one wastewater treatment plant is shown (indicated there by a single dark triangle),
supported by six pumping stations (indicated there by bright rectangles connected to dashed lines) and
several kilometres of a trunk pipe.
NOTE There are cases in small rural communities in which the communal decentralized wastewater treatment
and reuse systems are not equipped to treat sludge. In such cases, the sludge generated in these facilities is collected
and brought to centralized wastewater treatment plants for treatment.
© ISO 2023 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO/FDIS 24575:2023(E)
75 Generalized elements of wastewater treatment and reuse systems
7.15.1 General
In the planning of wastewater management systems for reuse or other purposes, there are many
components and subsystems to be selected and designed, as listed in 5.25.2 to 5.55.5. All costs associated
with all these elements of the system should be included in the cost comparison of different degrees of
distribution of the entire plan.
The following subsections provide context, along with a brief explanation of the nature and scope of each
of these elements.
7.25.2 Collection
The collection system is roughly divided into stages from the source towards its final destination, as
[11[11] ]
shown in available publications. . For the purposes of this document, the following notation will be
followed in order of flow -, from each home in a lateral sewer up to the intercepting sewer or pressure
[12[12] ]
main that reaches the wastewater treatment plant (based on EPA notation ): ): a) lateral sewer,;
b) branch sewer,; c) trunk sewer (main sewer),); d) intercepting sewer,; e) pressure main.
Systems may have all or part of these collection system components for different degrees of distribution.
For example,,, an onsiteon-site treatment system will typically only have a lateral sewer collecting from
the dwelling to the treatment system.
Trucking or hauling of wastewater or sludge is sometimes an alternative to collection and conveyance
systems, especially in non-sewered systems or onsiteon-site treatment systems. When any part of the
wastewater is disposed of by trucking or hauling, it is accounted for as an operational cost instead of an
investment cost.
7.35.3 Conveyance
Pumping stations and lift stations are used whenever wastewater conveyance by gravity is not possible,
either as an intermediate or final run of part of the collection system. Different designs are common for a
[13], [14 [13,14]]
sewage pumping or lift station, with the following typical main components: :
a) a) screening to protect the pumps from clogging;
b) b) a pit or a well to intercept the sewage and provide an operational volume and buffering;
c) c) pumps, including redundancy;
d) d) discharge pressure piping;
e) e) venting and optional means for odour control.
Vacuum collection systems are a recent alternative to gravity collection systems when the latter are not
practicable due to area limitation. The vacuum collection sewers use suction (negative pressure) to move
[15], [16 [15,16]]
the sewage through the following three main stages: :
— — Vacuum valve pit: sewage collection from individual households or homes by gravity. Once the
pit is full, a valve is opened and atmospheric pressure forces the wastewater to the vacuum branches.
— — Vacuum mains: a network of vacuum piping collecting sewage from the collection chambers of
individual housings and gradually converging towards the vacuum station. The pressure difference
between the valve pit and the vacuum station pulls the wastewater through the vacuum mains.
— — Vacuum station: producing the suction for the vacuum piping network connected to it and
typically pumping the sewer to the wastewater treatment plant.
It is reiterated that trucking or hauling of wastewater or sludge is sometimes an alternative to collection
and conveyance systems, especially in non-sewered systems or onsiteon-site treatment systems. When
any part of the wastewater is disposed of by trucking or hauling, it is accounted for as an C operating cost
O
instead of an C investment cost.
I
4 © ISO 2023 – All rights reserved
---------------------- Page: 10 ----------------------
ISO/FDIS 24575:2023(E)
7.45.4 Treatment
The treatment plant, also referred to as a WRRF, includes all installed water treatment processes used to
achieve compliance with local discharge standards or reuse requirements. These typically include the
[17[17]]
process sub-sections or categories described as follows and summarized in Table C.1Table C.1.
In cases where different effluent requirements are applicable for different plant sizes, such as between a
decentralized plant and a centralized plant, each plant or plan may be made with the requirements for its
type, as would be the eventual design for regulatory approval. For example, in some places, small
wastewater treatment and reuse systems are not required to perform tertiary treatment for reuse in
irrigation of tree-grown crops, whereas a large plant would beis required to perform tertiary treatment
regardless. In such cases, the cost of tertiary treatment does not have to be included where it is not
needed.
a) a) Pre-treatment: physical processes to remove elements that mightcould damage downstream
equipment and also remove easily removable constituents to improve downstream process
efficiency. Usually, pre-treatment units are designed to handle diurnal and seasonal flow variations.
The costing of pre-treatment shall include any aeration, mixing, chemicals, sludge treatment and
disposal, whether constant, periodic or occasional over the costing period. The pre-treatment
process contains some or all of the following main units:
— — Screening: removal of large particulate matter and objects that can usually be disposed of
as trash. There are manual or mechanical screens and the screens openings can be coarse or
fine. Screening is often installed in two stages, with a coarse screen followed by a fine screen.
— — Grit and grease removal unit: removes sand and gravel as well as fat, oil and grease.
— — Equalization tank: equalizes flowrates and organic loads in order to reduce the size and
cost of downstream units and to achieve constant loads on the process units. It should be
considered that smaller sewer systems have a higher ratio of peak flow to average flow than
larger systems.
b) b) Primary treatment: partial removal of suspended solids by gravity in a sedimentation tank or
pond. The quantity of sludge discharged from this operation shall be included in sludge treatment
cost calculations. If chemicals are added to the primary treatment, their cost shall be included in the
plant operating cost.
c) c) Secondary treatment: a biological treatment process, including separation between solids and
liquidliquids, such as a secondary clarifier or membrane separation. Such processes are typically
based on suspended biomass, such as the activated sludge process, SBR or MBR, a biofilm process or
a combination of both, such as MBBR, IFAS, MABR o
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 24575
ISO/TC 282/SC 2
General principles and guidelines
Secretariat: SAC
for cost analysis in planning of
Voting begins on:
2023-03-01 decentralized wastewater treatment
and/or reuse
Voting terminates on:
2023-04-26
Member bodies are requested to consult relevant national interests in ISO/TC
224 before casting their ballot to the e-Balloting application.
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 24575:2023(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 2023
---------------------- Page: 1 ----------------------
ISO/FDIS 24575:2023(E)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 24575
ISO/TC 282/SC 2
General principles and guidelines
Secretariat: SAC
for cost analysis in planning of
Voting begins on:
decentralized wastewater treatment
and/or reuse
Voting terminates on:
Member bodies are requested to consult relevant national interests in ISO/TC
224 before casting their ballot to the eBalloting application.
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
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.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
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OF ANY RELEVANT PATENT RIGHTS OF WHICH
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IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: copyright@iso.org
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO
ISO/FDIS 24575:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
© ISO 2023 – All rights reserved
NATIONAL REGULATIONS. © ISO 2023
---------------------- Page: 2 ----------------------
ISO/FDIS 24575:2023(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 2
3.1 Terms and definitions . 2
3.2 Symbols and abbreviated terms . 2
4 Description of different degrees of distribution in planning and design .3
5 Generalized elements of wastewater treatment and reuse systems .4
5.1 General . 4
5.2 Collection . 4
5.3 Conveyance . 4
5.4 Treatment . 5
5.5 Effluent reuse management . 7
6 Cost items to be considered in economic life cycle analysis calculations .7
6.1 General . 7
6.2 Investment cost (C ) or CAPEX items . 7
I
6.2.1 General . 7
6.2.2 Sewer collection piping, C . 8
I,A
6.2.3 Pumping stations, C . 8
I,B
6.2.4 The treatment plant, C . 8
I,C
6.2.5 Effluent distribution piping, C . 9
I,D
6.2.6 Effluent pumping stations, C . 9
I,E
6.2.7 Treated water reservoirs, C . 9
I,F
6.3 Operating cost (C ) OPEX items . 9
O
6.3.1 General . 9
6.3.2 Electricity, C . 10
O,A
6.3.3 Labour, C . 10
O,B
6.3.4 Chemicals, C . 10
O,C
6.3.5 Sludge disposal, C . 11
O,D
6.3.6 Services, C . 11
O,E
6.3.7 Others, C . 11
O,F
6.4 Maintenance cost items (C ) . 11
M
6.5 Income or revenue: negative cost items (C ) .12
N
6.5.1 General .12
6.5.2 Income from selling treated water for reuse, I .12
w
6.5.3 Income from biogas and its products, I .12
G
6.5.4 Income from selling recovered products, I .13
S
6.5.5 Other income, I . 13
O
7 Cost calculations, factoring and results integration .14
7.1 General . 14
7.2 Conversion of all costs to present value . 14
7.3 Normalization of all costs per unit . 15
8 Reporting on results of economic life cycle analysis calculations .15
Annex A (informative) Cost calculation example .17
Annex B (informative) Correlations for CAPEX and OPEX of different process units in
a treatment plant for reuse . .19
Annex C (informative) Summary of treatment process units along with their associated
cost items .20
iii
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ISO/FDIS 24575:2023(E)
Bibliography .21
iv
© ISO 2023 – All rights reserved
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ISO/FDIS 24575:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and nongovernmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (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, in collaboration with Technical Committee ISO/TC 224 Drinking water,
wastewater and stormwater systems and services.
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.
v
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ISO/FDIS 24575:2023(E)
Introduction
While energy consumption for water and wastewater treatment is significant, up to 80 % of it is used
for conveyance. This includes pumping of wastewater to the treatment facility and pumping the effluent
to its reuse site. In centralized wastewater treatment and reuse system schemes, the long-distance
conveyance through piping systems and pumping stations is also associated with capital investment,
[1],[2]
which would be hard to bear for those people living in areas of low population densities. Thus, a
network of decentralized wastewater treatment and reuse systems will potentially reduce both the
capital expenses (CAPEX) and operating expenses (OPEX) in some cases, compared with conventional
planning of centralized wastewater treatment and reuse systems. Another benefit of decentralized
[3],[4]
treatment is enabling local reuse, mainly for irrigation.
Distributed design is the concept of providing several decentralized wastewater treatment systems
instead of one central plant, as outlined in other International Standards, such as ISO 23056, which
defines and describes different degrees of decentralization of wastewater treatment plants and
discusses considerations that should be taken in the selection of each alternative. Due to development
in automation and telecommunication, as well as in biological wastewater treatment processes, the
distributed design concept has become a viable option. Potential savings in using distributed design
include:
— lower collection and pumping system construction costs;
— lower collection and pumping system operation and maintenance costs;
— lower energy consumption for pumping;
— local availability for reuse in agriculture or industry or landscape irrigation.
However, potential drawbacks include:
— higher specific cost of each plant compared with a centralized wastewater treatment and reuse
system;
— higher operator attention required for many plants compared with one plant.
This document aims to provide guidelines for life cycle cost assessment for any degree of distribution in
the planning of a network of decentralized wastewater treatment and reuse systems in order to enable
the cost optimization of the design.
vi
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---------------------- Page: 6 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 24575:2023(E)
General principles and guidelines for cost analysis in
planning of decentralized wastewater treatment and/or
reuse
1 Scope
This document specifies the general principles and provides guidance on the quantitative
characterization of the life cycle cost of a complete wastewater management system, including collection,
treatment and, optionally, reuse. It enables the consideration of different degrees of distribution,
including non-sewered systems for one or more dwellings and associated trucking operations.
The methodology provided in this document is applicable to urban or rural areas wherein several
decentralized wastewater treatment and reuse systems can provide a lower cost solution than a single
centralized plant. Similarly, the same methodology can be applied for industrial reuse systems, where
several separate plants on a large industrial site can be considered instead of one treatment system.
The scope of this document includes the following:
a) Guidance on the determination of the degrees of distribution of decentralized wastewater
treatment and reuse systems.
b) A definition of the elements and components included in the life cycle cost of the different degrees
of distribution in wastewater management systems, including construction, operation and
maintenance.
c) Guidance on the required steps for calculating life cycle cost indicators, including considerations of
term and interest, operation and maintenance, replacement parts, equipment life expectancy, the
value of water for reuse and other income from by-products.
d) A definition of the metrics for reporting results, including the cost per unit, scope, term and interest.
The following secondary costs and other considerations are not within the scope of this document:
— cost of eventual disposal of the system;
— guidance on wastewater treatment process selection and design;
— health and sustainability considerations (although health and sustainability are primary
considerations in design and decisions);
— social impact factors and/or environmental risks and impacts.
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
1
© ISO 2023 – All rights reserved
---------------------- Page: 7 ----------------------
ISO/FDIS 24575:2023(E)
3 Terms, definitions, symbols and abbreviated terms
3.1 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/
3.1.1
distributed system
two or more treatment plants in different geographical locations linked to a central system, either
physically or by management
[6]
Note 1 to entry: See WEF Fact Sheet “Distributed Systems Overview” (ref. WSEC-2019-FS-012).
3.1.2
degree of distribution
number of treatment plants to treat a certain population
Note 1 to entry: A high degree of distribution means many plants to treat the population, while a low degree of
distribution means a number as low as one centralized plant to treat that same population.
3.1.3
non-sewered system
NSS
system that is not connected to a networked sewer and collects, conveys and fully treats the specific
input to allow for safe reuse or disposal of the generated solid output and/or effluent
Note 1 to entry: A non-sewered system is also referred to as an “on-site treatment system”, see ISO 24513:2019,
3.5.16.
[SOURCE: ISO 30500:2018, 3.1.1.1, modified — Note to entry replaced.]
3.1.4
total installed cost
final cost of designing, fabricating and building a capital project or industrial asset
Note 1 to entry: The total installed cost includes the cost of labour and materials.
3.2 Symbols and abbreviated terms
AOP advanced oxidation processes
C investment cost
I
C maintenance cost
M
C negative cost
N
C operating cost
O
CAPEX capital expenses
IFAS integrated fixed-film activated sludge
MABR membrane aerated biofilm reactor
2
© ISO 2023 – All rights reserved
---------------------- Page: 8 ----------------------
ISO/FDIS 24575:2023(E)
MBBR moving bed bio reactor
MBR membrane bio reactor
NPV net present value
OPEX operating expenses
PE population equivalent
PV present value
RO reverse osmosis
SBR sequencing batch reactor
UASB upflow anaerobic sludge blanket
UV ultraviolet (irradiation, in context of disinfection)
WRRF water resource recovery facility
4 Description of different degrees of distribution in planning and design
The difference between decentralized wastewater treatment systems (3.1.1) and distributed
wastewater treatment systems (see ISO 20670) is that distributed systems are located in different
geographical locations but are linked to a central system either physically or by management, whereas
decentralized systems can be located in a different geographical location but are not linked physically
or are not managed under the umbrella of a centralized system.
The degree of distribution (3.1.2), meaning the number of treatment units for a given population, can be
as high as one system for each household (on-site systems) or as low as one single treatment plant for
a city, town or village (centralized system), or many degrees in between, such as one system per street
or one system for every cluster of households or drainage basin. The collection of wastewater can be
via a piped network (a sewer system) or by motorized vehicles, such as vacuum trucks, in non-sewered
systems. Determining the required number of systems can be challenging in the design of a wastewater
treatment and reuse plan. In some cases, the means to meet this challenge can be through an economic
estimation of the longterm cost.
A single large plant may benefit from the economy of scale of its equipment and from lower operation
and maintenance costs compared with a distributed system made up of multiple decentralized systems.
However, distributed systems can offset much of this benefit through lower CAPEX for piping and
pumping as well as lower OPEX for pumping energy, on both wastewater and water for reuse. Therefore,
the overall cost benefit of a distributed design or a centralized design changes from one place to another
and should be calculated in order to make a decision based on costs.
A structured analysis of the total cost per unit of wastewater treatment for reuse was demonstrated
by multiple computerized simulations for different types of terrain and different population densities.
[9]
The results show that for the lowest population density found in rural areas, the highest degree
of distribution is associated with the lowest cost in flat, hilly or mountainous terrains, whereas in
suburban areas it greatly depends upon the terrain. A less distributed design results in a lower cost in
flat terrain, whereas a more distributed design results in a lower cost in mountainous terrain.
[10]
An example of two different degrees of distribution for a specific case is given by van Afferden et al.,
showing a distributed scenario of nine decentralized systems (indicated there by white triangles with
a dark frame) and just one pumping station, all managed by one utility. For comparison, a centralized
scenario with one wastewater treatment plant is shown (indicated there by a single dark triangle),
3
© ISO 2023 – All rights reserved
---------------------- Page: 9 ----------------------
ISO/FDIS 24575:2023(E)
supported by six pumping stations (indicated there by bright rectangles connected to dashed lines) and
several kilometres of a trunk pipe.
NOTE There are cases in small rural communities in which the communal decentralized wastewater
treatment and reuse systems are not equipped to treat sludge. In such cases, the sludge generated in these
facilities is collected and brought to centralized wastewater treatment plants for treatment.
5 Generalized elements of wastewater treatment and reuse systems
5.1 General
In the planning of wastewater management systems for reuse or other purposes, there are many
components and subsystems to be selected and designed, as listed in 5.2 to 5.5. All costs associated
with all these elements of the system should be included in the cost comparison of different degrees of
distribution of the entire plan.
The following subsections provide context, along with a brief explanation of the nature and scope of
each of these elements.
5.2 Collection
The collection system is roughly divided into stages from the source towards its final destination, as
[11]
shown in available publications. For the purposes of this document, the following notation will be
followed in order of flow, from each home in a lateral sewer up to the intercepting sewer or pressure
[12]
main that reaches the wastewater treatment plant (based on EPA notation ): a) lateral sewer;
b) branch sewer; c) trunk sewer (main sewer); d) intercepting sewer; e) pressure main.
Systems may have all or part of these collection system components for different degrees of distribution.
For example, an on-site treatment system will typically only have a lateral sewer collecting from the
dwelling to the treatment system.
Trucking or hauling of wastewater or sludge is sometimes an alternative to collection and conveyance
systems, especially in non-sewered systems or on-site treatment systems. When any part of the
wastewater is disposed of by trucking or hauling, it is accounted for as an operational cost instead of an
investment cost.
5.3 Conveyance
Pumping stations and lift stations are used whenever wastewater conveyance by gravity is not possible,
either as an intermediate or final run of part of the collection system. Different designs are common for
[13], [14]
a sewage pumping or lift station, with the following typical main components:
a) screening to protect the pumps from clogging;
b) a pit or a well to intercept the sewage and provide an operational volume and buffering;
c) pumps, including redundancy;
d) discharge pressure piping;
e) venting and optional means for odour control.
Vacuum collection systems are a recent alternative to gravity collection systems when the latter are
not practicable due to area limitation. The vacuum collection sewers use suction (negative pressure) to
[15], [16]
move the sewage through the following three main stages:
— Vacuum valve pit: sewage collection from individual households or homes by gravity. Once the pit is
full, a valve is opened and atmospheric pressure forces the wastewater to the vacuum branches.
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ISO/FDIS 24575:2023(E)
— Vacuum mains: a network of vacuum piping collecting sewage from the collection chambers of
individual housings and gradually converging towards the vacuum station. The pressure difference
between the valve pit and the vacuum station pulls the wastewater through the vacuum mains.
— Vacuum station: producing the suction for the vacuum piping network connected to it and typically
pumping the sewer to the wastewater treatment plant.
It is reiterated that trucking or hauling of wastewater or sludge is sometimes an alternative to collection
and conveyance systems, especially in non-sewered systems or on-site treatment systems. When any
part of the wastewater is disposed of by trucking or hauling, it is accounted for as an operating cost
instead of an investment cost.
5.4 Treatment
The treatment plant, also referred to as a WRRF, includes all installed water treatment processes used
to achieve compliance with local discharge standards or reuse requirements. These typically include
[17]
the process subsections or categories described as follows and summarized in Table C.1.
In cases where different effluent requirements are applicable for different plant sizes, such as between
a decentralized plant and a centralized plant, each plant or plan may be made with the requirements
for its type, as would be the eventual design for regulatory approval. For example, in some places, small
wastewater treatment and reuse systems are not required to perform tertiary treatment for reuse
in irrigation of tree-grown crops, whereas a large plant is required to perform tertiary treatment
regardless. In such cases, the cost of tertiary treatment does not have to be included where it is not
needed.
a) Pre-treatment: physical processes to remove elements that could damage downstream equipment
and also remove easily removable constituents to improve downstream process efficiency. Usually,
pre-treatment units are designed to handle diurnal and seasonal flow variations.
The costing of pre-treatment shall include any aeration, mixing, chemicals, sludge treatment and
disposal, whether constant, periodic or occasional over the
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