A method to calculate and express energy consumption of industrial wastewater treatment for the purpose of water reuse

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 consumption involved in office operation. — Energy recovery from processes such as anaerobic reactors producing biogas. Filtration processes, which are sometimes part of the biological treatment process and at other times part of the post treatment, are referred to separately within this document.

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Status
Published
Publication Date
23-May-2019
Current Stage
6060 - International Standard published
Start Date
18-Apr-2019
Completion Date
24-May-2019
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ISO 21939-1:2019 - A method to calculate and express energy consumption of industrial wastewater treatment for the purpose of water reuse
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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 21939-1:2019(E)
ISO 2019
---------------------- Page: 1 ----------------------
ISO 21939-1:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

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

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below or ISO’s member body in the country of the requester.
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Published in Switzerland
ii © ISO 2019 – All rights reserved
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ISO 21939-1:2019(E)
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

© ISO 2019 – All rights reserved iii
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ISO 21939-1:2019(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 4,

Industrial water reuse.

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.
iv © ISO 2019 – All rights reserved
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ISO 21939-1:2019(E)
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.

© ISO 2019 – All rights reserved v
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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 consumption involved in office operation.
— Energy recovery from processes such as anaerobic reactors producing biogas.

Filtration processes, which are sometimes part of the biological treatment process and at other times

part of the post treatment, are referred to separately within this document.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 20670, Water reuse — Vocabulary
© ISO 2019 – All rights reserved 1
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ISO 21939-1:2019(E)
3 Terms and 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 terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.2 Symbols and abbreviated terms
A O anaerobic-anoxic-oxic wastewater treatment process

Bardenpho a process for biological nutrient removal developed by James Barnard of South Africa

in the 1970’s

BOD bio-chemical oxygen demand (5 days) concentration or load, mg/l or kg/d, respectively

COD chemical oxygen demand concentration or load, mg/l or kg/d, respectively
DAF dissolved air flotation
DO dissolved oxygen
DGF dissolved gas flotation
MBR membrane bio-reactor
MLE modified Ludzack Ettinger process of wastewater treatment
NEC normalized energy consumption, kWh/kg
NO -N net oxidizable mass removed
TN total nitrogen concentration or load, mg/l or kg/d, respectively
UCT University of Cape Town process of wastewater treatment
VIP Virginia Initiative Plant process of wastewater treatment
VFD variable frequency drive
RBC rotating biological contactor
TF trickling filter
TKN total Kjeldahl nitrogen concentration or load, mg/l or kg/d, respectively
VSS volatile suspended solids
4 Expression and normalization of energy consumption
4.1 Energy consumption indicator

Following are details and explanations of values needed for later calculations in 4.2.

2 © ISO 2019 – All rights reserved
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ISO 21939-1:2019(E)

4.1.1 Normalized energy consumption shall be expressed in terms of energy per net oxidizable mass

removed.
4.1.2 The net oxidizable mass removed (NOR) shall comprise of
— COD removed,
— TKN removed,
— Nitrate created (or subtraction of nitrate removed).

4.1.3 Constituents included in the indicator shall be factored for their oxygen demand value. Specifically

the following factoring principles shall be applied, based on the references indicated in Annex A and in

References [1], [2] and [5].
— COD removed shall be multiplied by +1,0.

— In design, COD concentration in the sludge shall be calculated on the basis of VSS concentration

multiplied by 1,42 (References [8], [12], Annex A); the VSS concentration in the sludge, taken for

calculations in this document, shall be the same as the value for VSS concentration in the sludge

taken in process design. Process design values for sludge composition can be calculated according

to conventional design procedures (Reference [8], Annex A).

— TKN removed shall be multiplied by +1,71 (corresponding to oxidation to nitrogen gas regardless of

the chemical pathway).

NOTE The fraction of TKN which was not reduced to zero-valence nitrogen is accounted for as nitrate

and nitrite, with the multipliers as specified below.

— In design, TKN concentration in the sludge shall be calculated as 12 % of the VSS, on the basis

described above for COD calculation
...

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