ISO 21939-1:2019

INTERNATIONAL ISO
STANDARD 21939-1
First edition
2019-05
A method to calculate and express
energy consumption of industrial
wastewater treatment for the purpose
of water reuse —
Part 1:
Biological processes
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions, symbols and abbreviated terms . 2
3.1 Terms and definitions . 2
3.2 Symbols and abbreviated terms. 2
4 Expression and normalization of energy consumption . 2
4.1 Energy consumption indicator . . 2
4.2 Calculation . 4
5 Components contribution to the energy consumption . 4
5.1 General . 4
5.1.1 Steady state conditions . 4
5.1.2 Consideration of flow rate . 5
5.1.3 Calculation of variable consumptions . 5
5.1.4 Accounting for addition of oxidizing chemicals . 5
5.1.5 Physico-chemical separation pre-treatment processes . 5
5.2 List of system components . 6
5.2.1 General. 6
5.2.2 Aeration and combined mixing and aeration equipment . 6
5.2.3 Mixing . 6
5.2.4 Solid-liquid separation . 6
5.2.5 Internal circulation pumping . 6
5.2.6 Circulation of settled sludge . 6
5.2.7 Other pumping. 6
5.2.8 Air driven pumping and/or mixing . 6
6 Factoring of different process conditions . 7
6.1 General . 7
6.2 Temperature adjustments . 7
6.3 Barometric pressure adjustment . 7
6.4 Type of wastewater . 7
Annex A (informative) References to formulae and calculations . 8
Annex B (informative) Example calculations. 9
Bibliography .12
Foreword
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electrotechnical standardization.
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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
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This document was prepared by Technical Committee ISO/TC 282, Water reuse, Subcommittee SC 4,
Industrial water reuse.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv © ISO 2019 – All rights reserved

Introduction
Biological wastewater treatment is a major process step in many cases of industrial wastewater
treatment for reuse.
In the field of biological wastewater treatment, the energy consumption of the process is commonly
normalized in order to account for difference in flow and concentration when comparing different
treatment options. For example, energy consumption is reported per unit volume of wastewater treated
(e.g. kWh/m ) or per unit of pollutant removed BOD (e.g. kWh/kg BOD ), TN (e.g. kWh/kg TN).
5 5
The disadvantages and limitations of these indicators include:
— Neither of the existing indicators are agreed to and accepted as a standard in the industry;
— They do not provide means to compare nitrifying processes to non-nitrifying processes;
— There is no differentiation between design values and measured values, and there are no standard
methods to obtain the indicator for each case.
Another approach is to report on the results from standard tests in water as oxygen transfer capacity
per unit energy consumed (e.g. kg O /kWh).
The disadvantages and limitations of this type of indicator include:
— It is less convenient for the market to apply to its cases, (for example because not all removal is by
oxidation, some is by metabolic consumption);
— It only considers oxygen transfer equipment or processes able to dissolve oxygen in water, which
does not apply to all biological treatment processes (such as rotating biological contactor (RBC) and
trickling filter (TF)).
These issues are discussed in the literature, which compares results expressed in different ways and
correspondingly provides contradicting indications (see References [4], [5] and [10]).
Therefore this document aims to create a quantitative measure for universal characterization of the
energy consumption for aerobic biological wastewater treatment systems. Such standardization will
benefit engineers in specification of systems and comparison of systems. The need arises especially in
consideration of life cycle cost of a wastewater treatment system.
NOTE 1 Normalized energy consumption of wastewater treatment systems typically decreases with
increasing size of the system, mainly due to higher efficiency of larger electromechanical equipment such as
pumps and blowers. Thus, large wastewater treatment plants will have lower normalized energy consumption
than small wastewater treatment systems. In order to neutralize the influence of plant size in comparison of
energy consumption, a correlation such as published by Silva, C., et al. (see Reference [11]) can be used, regardless
of this document.
NOTE 2 Higher effluent quality requirements are generally associated with higher normalized energy
consumption. Typically, normalized energy consumption will be compared for similarly performing systems.
However, it is possible, for example, to present the normalized energy consumption for different treatment
qualities as such.
NOTE 3 This document quantifies the energy consumption, regardless of treatment efficiency that can vary
for different types of wastewater. Treatment efficiency might typically be characterized by retention time and/or
volumetric loading rate and/or volumetric removal rate or other indicators which are not part of this document.
INTERNATIONAL STANDARD ISO 21939-1:2019(E)
A method to calculate and express energy consumption
of industrial wastewater treatment for the purpose of
water reuse —
Part 1:
Biological processes
1 Scope
This document sets out the general principles for, and provides guidance on, the quantitative
characterization of the energy consumed by industrial biological wastewater treatment systems. It
does not aim to characterize the treatment pollutants removal performance or process reliability or
any other consideration in the selection of a wastewater treatment system.
This document includes the following sub-systems of biological treatment system:
— Biological reactors, which might be suspended growth or fixed film processes or a combination
thereof, and can include anaerobic, anoxic and/or aerobic tanks and/or zones.
— Solid-liquid separation processes such as sedimentation, flotation, or membrane filtration, used for
clarification of the water before discharge to downstream processes, which can also involve the
return of a the separated solids as sludge back to the biological reactor.
— Any pumps, blowers and mixers for water circulation, mixing and air supply in and between the
sub-systems listed herein.
— Heating or cooling of the water for treatment.
This document does not include the following subsystems of the biological treatment system:
— Wastewater feed pumps.
— Pre-treatment systems, which for the purposes of this document also include preliminary and
primary treatment processes, such as but not limited to, screening, sedimentation, dissolved air
flotation, chemical oxidation, oil separation.
— Post-treatment processes, such as but not limited to, disinfection, desalination, ion exchange, sludge
treatment and handling systems.
— Site lighting or any energy consumpt
...