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
General Information
Standards Content (Sample)
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 2023
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Published in Switzerland
ii
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
Bibliography .21
iv
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
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on the ISO list of patent declarations received (see www.iso.org/patents).
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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
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
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
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
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),
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.
— 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 constructed wetlands, including tidal,
aeration ponds or a lagoon system. OPEX items of secondary treatment include:
— electricity for aeration with blowers or aerators or other means;
— electricity for pumping, in circulation of sludge or tank content or other;
— electricity consumption for mixing, agitation, raking and any other similar electromechanical
drives;
— chemicals added to the process for coagulation or other purposes;
— replacement parts, such as UV lamps, membranes, pumps and other items which have a shorter
life expectancy (shorter period of amortization) than the period taken for life cycle cost
calculation;
— labour for operation, maintenance, analysis and other;
— any other directly related specific cost item.
d) In some cases, following secondary treatment, filtration and/or disinfection is performed, mainly
to reduce suspended solids, turbidity, phosphorus and microorganisms or pathogens.
The filtration could require any of the following, according to equipment selection as part of the
design: pumping through the filters, backwashing, chemical dosing for coagulation or cleaning, air
scouring. The corresponding OPEX items will be the power consumption of the pumps and blowers
and the cost of the chemicals used for either coagulation or cleaning.
Chemical disinfection is typically performed by chlorine or chlorine derivatives, ozone or hydrogen
peroxide. The associate OPEX items are the cost of the chemicals or the electricity cost of production
of the oxidant. For example, disinfection with ozone could use an ozone generator from oxygen
produced by a pressure swing adsorption system, in which case the electricity consumption of
both units shall be included in the disinfection cost.
Alternatively, UV irradiation is selected as part of the design, in which case the power consumption
is the main OPEX item.
e) Advanced treatment (sometimes referred to as quaternary treatment) is all downstream treatment
processes following tertiary treatment and typically involves RO and/or AOP.
RO is originally a membrane filtration process to separate dissolved salts, but also removes viruses,
bacteria and micropollutants. Its main OPEX items are the electricity for high-pressure pumping,
constant dosing and periodical cleaning chemicals, membranes and other replacement parts.
AOP is currently based on enhancement of an oxidation process, such as ozonation combined with
UV. OPEX items for AOP processes depend on the processes selected in design, and can be chemicals
and/or power consumption, as well as replacement parts.
f) Sludge management, including sludge treatment and disposal, refers to all processes and activities
carried out to handle and dispose of generated primary and/or secondary sludge. It can include
stabilization and dewatering or just hauling off-site for treatment elsewhere, according to design.
Sludge processing is typically associated with a cost and is targeted at reducing the volume of
remaining sludge to be disposed of at a higher cost. For example, a sludge management plan could
comprise accumulation and occasional disposal by hauling off-site at a high cost or it could comprise
thickening, stabilization and dewatering to a smaller volume with little additional processing
requirements.
Sludge treatment is usually a multistage process, generally including thickening, stabilization and
dewatering:
— Thickening can be by gravity or by mechanical thickeners.
— Stabilization can be by aerobic, anaerobic or chemical processes. Aerobic sludge digestion has a
major OPEX item in power consumption for aeration, whereas anaerobic digestion typically has
a higher OPEX item in labour and maintenance (replacement parts). Anaerobic digestion can
have a negative OPEX item through sales of biogas or electricity or steam.
Chemical stabilization uses mixing of thickened sludge with a chemical such as lime, usually
with another inert powder, both of which are usually OPEX items.
— Dewatering is carried out using different types of suitable electromechanical equipment, such
as a centrifuge, a belt press or a multi-disc screw. Dewatering usually requires a combination of
electrolytes and polymers for coagulation and flocculation. Thus, the OPEX items of dewatering
shall include power consumption and chemicals. In addition, there are typically high operator
costs and high maintenance costs for replacement parts that contribute to the OPEX.
Typically, a centrate stream, which is the filtrate from sludge dewatering, is generated from
dewatering. All costs for treatment of the centrate stream (sidestream) shall be included in
the cost of dewatering, for example chemical dosing for phosphorous or struvite removal or a
biological treatment process such as anammox.
— Dewatered stabilized sludge is disposed of or treated to comply with higher requirements
by means such as heating, composting or other processes. As a result, the disposal costs will
possibly be lower or even negative (an income). The cost of energy and chemicals to obtain this
higher sludge quality (known in some places as “class A” sludge) shall be included in the OPEX.
In addition, the projected cost of disposal or the income from selling the sludge shall be included
in accordance with Clause 6.
NOTE 1 The replacement of UV lamps, membranes and pump components is covered in Clause 6.
NOTE 2 All components of the system have maintenance costs associated with them.
For a summary of treatment process units along with their associated cost items, see Annex C and
Table C.1.
5.5 Effluent reuse management
Reuse can involve any aspect of the transportation and storage of treated water, including an
operational volume, pumping stations, effluent piping (“purple” pipes) and water reservoirs, such as
seasonal reservoirs.
All elements of the water reuse systems within the scope of the plan will be considered for their cost,
including energy consumption for pumping, chemical dosing and/or aeration in the reservoir.
6 Cost items to be considered in economic life cycle analysis calculations
6.1 General
Each of the components of the water network should account for both their OPEX and CAPEX.
6.2 Investment cost (C ) or CAPEX items
I
6.2.1 General
Primarily, the basis for estimation of the investment cost of each item should be the same for every
degree of distribution. For example, prices of certain items (such as pipes) are taken from price tables
for all plans being compared. Alternatively, the same pricing key, such as a price per unit, is applied in
all plans for a certain item. For example, in pipes it could be price per unit length and per unit diameter
($/m/mm).
The total investment cost is the sum of the costs of the components or items included in the plan for
each degree of distribution, as defined in Formula (1).
CC= (1)
II∑ ,i
i
where
C is the total investment cost;
I
C is the cost of item i;
I,i
I A, B, C, D, E or F, corresponding to 6.2.2 to 6.2.7.
6.2.2 Sewer collection piping, C
I,A
A complete and real cost of a plan should include all levels of the collection piping, starting with lateral
sewers from the sources or households, gradually converging into larger and fewer collectors that
eventually direct the sewage to treatment plants.
For the purpose of comparison between two or more plans, the common part of the sewer system
may be eliminated. For example, if the two alternatives described in Clause 4 are compared, the cost
comparison may include only piping starting from the locations of the decentralized plants of the
distributed design, up to which both systems are identical, i.e. the piping cost for comparison may
exclude the common sections of the two plans.
The total installed cost of the collection piping should be taken for C . If no piping is installed, such
I,A
as in the case of non-sewered systems or an on-site treatment system, the total installed cost of the
collection piping will be zero.
6.2.3 Pumping stations, C
I,B
The cost of pumping stations shall include all related civil and infrastructure, such as concrete
construction works, fence and electricity connection (installed cost). The cost may be obtained through
specific pricing or through published correlations or even proprietary correlations. However, the same
methodology should be applied to all plans being compared. For the sake of clarity, if there are no
pumping stations, such as in the case of decentralized or on-site treatment system, the cost of pumping
stations shall be zero.
6.2.4 The treatment plant, C
I,C
The cost of the complete treatment plant requires some level of process design in order to define the
type of process and its main units. For the purpose of cost comparisons, the costs of different plant
sizes may be estimated in any of the following methodologies (as long as all degrees of distribution
follow the same methodology):
— offers or price lists from contractors or suppliers (usually will require some level of equipment
sizing);
[18]
— scale-up rules based on known prices for a similar scope, such as capacity-ratio exponents;
— published or proprietary correlations, such as shown in Annex B, for which more detail can be found
at the referenced source; however, the use of any published or proprietary correlations should be
exercised at the discretion of a professional with understanding of their applicability to the case.
The effluent quality requirements and the intended reuse application can be different for small local
plants and large centralized plants. These conditions may be considered in the design of the treatment
systems for each case, so a different process and technology may be chosen for different degrees of
distribution.
In some cases, landscaping or other development work is required from a local small plant located close
to the source. The cost of this mandatory requirement, which may be different between small, local
systems and larger, remote systems, should be included as part of C .
I,C
6.2.5 Effluent distribution piping, C
I,D
Treated water distribution can be different for different degrees of distribution. The plans should
specify the reuse destinations and quantify the water distribution or discharge piping.
The distribution piping pricing, C , shall be for the installed cost and should follow the same principals
I,D
for the different degrees of distribution being compared, preferably based on the same sources.
If the treated water distribution is not part of the plan due to ownership or scope by others, it may be
excluded from pricing.
6.2.6 Effluent pumping stations, C
I,E
The cost of pumping stations shall include all related civil and infrastructure works, such as concrete
construction, fence and electricity connection (installed cost).
The cost may be obtained through detailed itemized pricing or through published or proprietary
correlations. In any case, the same pricing methodology should be applied to all degrees of distribution
being compared.
If effluent pumping is not within the scope of the plan, it may be excluded from pricing.
6.2.7 Treated water reservoirs, C
I,F
If treated water reservoirs are within the scope of the plan, their cost shall be included as part of the
total CAPEX. Sizing of the reservoirs should match the reuse purpose and destination, which does not
have to be the same for different degrees of distribution. Land cost consideration may be taken into
account, preferably representing a real expense and not the potential value.
The basis for pricing may be according to detailed itemized costs or based on published or proprietary
correlations.
6.3 Operating cost (C ) OPEX items
O
6.3.1 General
Operating cost correlations could be available (see Table B.1) and generally include all of the cost
items in this subclause in one formula. Such correlations may be used as long as they are applied to all
compared plans of different degrees of distribution. These correlations calculate C directly.
O
If a correlation for C is not applicable or available, each of the cost items, C , should be accounted for
O O,i
in accordance with this subclause. The total operating cost is obtained using Formula (2):
CC= (2)
OO∑ ,i
i
where
C is the total operating cost;
O
C is the operating cost of item i;
I,i
i A, B, C, D, E or F, corresponding to 6.3.2 to 6.3.7.
NOTE The operating costs (C ) are expressed and directly related to unit treated (such as $/m ) and the
O
expenses are distributed over time, as opposed to the investment costs, which are a singular event expressed per
unit capacity [e.g. $/(m /d)]. Guidelines for amortization of distributed expenses to present value for expression
in the same terms of a singular expense, and vice versa, are provided in Clause 7.
6.3.2 Electricity, C
O,A
Power consumption for sewage pumping is typically estimated according to distance and elevation
(head or discharge pressure) for each branch of pressure sewer.
[19]
Wastewater treatment plant energy consumption may be estimated according to published or
proprietary values for each type of process, in terms of kWh/m . The processes selected may vary
between different plans but the methodology to attribute an energy consumption and the cost per unit
energy should be the same for all plans being compared.
Distribution of water for reuse, if within the scope of the plans being compared, may be estimated
according to distance and elevation (head or discharge pressure) for each branch of effluent distribution.
Calculation of the annual energy cost should typically follow these steps:
— the total power consumption of a plan should be obtained in units of power, such as kW;
— a price for electricity should be assigned in terms of currency per unit energy, such as $/kWh;
— the power consumption should be multiplied by the price to obtain cost per unit time (like cash
flow), such as $/h;
— the cash flow should be converted to the time scale of the amortization, such as $ per year, by
multiplying the cost per time (e.g. $/h) by time per year (e.g. 8 700 h/year).
6.3.3 Labour, C
O,B
The cost of labour shall be included in the operating cost. Typically, labour is required for sampling,
analysis, measurements, data collection and documentation, reporting, changing process conditions
and housekeeping. The operation of pumping stations is included in the labour cost of the plan.
NOTE Different degre
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