ISO 24261-2:2021

INTERNATIONAL ISO
STANDARD 24261-2
First edition
Fine bubble technology — Elimination
method for sample characterization —
Part 2:
Fine bubble elimination techniques
PROOF/ÉPREUVE
Reference number
ISO 24261-2:2021(E)
©
ISO 2021

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ISO 24261-2:2021(E)

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ISO 24261-2:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 2
4.1 Sample . 2
4.2 Measuring instruments . 2
5 Environment . 2
6 Elimination technique . 3
6.1 General . 3
6.2 Ultrasonication method . 3
6.2.1 General. 3
6.2.2 System configuration . 3
6.2.3 Key experimental variables for the ultrasound elimination technique . 4
6.2.4 Conditions and parameters to be tuned or optimized . 5
6.2.5 Procedure for parameter optimization . 5
6.3 Ultracentrifugation method . 5
6.3.1 General. 5
6.3.2 System configuration . 6
6.3.3 Specifications, conditions and parameters to be selected and predetermined . 6
6.3.4 Conditions and parameters to be tuned or optimized . 7
6.3.5 Procedure of parameter optimization . 7
6.4 Freeze and thaw . 7
6.5 Boiling and cooling . 8
Annex A (informative) Example of results for the ultrasonication method .9
Annex B (informative) Example of results for the ultracentrifugation method .10
Annex C (informative) Example of results for freezing (PTA method) .11
Bibliography .12
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ISO 24261-2:2021(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 281 Fine bubble technology.
A list of all parts in the ISO 20480 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO 24261-2:2021(E)

Introduction
Fine bubble technology has recently seen growth in its application to markets such as cleaning, water
treatment, agriculture and aquaculture and biomedical fields. Now methods are needed to evaluate the
efficacy and efficiency of generation systems. The characteristics of most importance are the number
concentration and size indices of the fine bubbles produced by such systems.
Furthermore, fine bubble dispersions in water can contain other solid and liquid particles. Contaminants
such as these particles make accurate characterization of fine bubbles extremely difficult. Therefore,
distinction of fine bubbles from contaminants is an urgent issue. This is also why the term index is used
as it can never be 100 % established that a particle is a bubble and not a contaminant.
Currently, there are several measurement methods widely used to evaluate the number concentration
index and the size index of particles. However, there are few methods to distinguish bubbles in fine
bubble dispersions from other particles.
If the bubbles can be totally eliminated (with no residual bubbles) by mechanisms such as dissolution
or flotation, this issue can be solved. If a method that eliminates fine bubbles in a specific size range
is used, it is potentially possible to distinguish fine bubbles from other solid and liquid particles. The
concentration of material after potential elimination can be compared in particle concentration index
to the liquid used prior to generation. If elimination has been successful, they should be the same, and
by this comparison, elimination techniques can be developed and optimized.
This document is intended to specify the most effective techniques for eliminating fine bubbles from
fine bubble dispersions in water and their optimization.
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INTERNATIONAL STANDARD ISO 24261-2:2021(E)
Fine bubble technology — Elimination method for sample
characterization —
Part 2:
Fine bubble elimination techniques
1 Scope
This document specifies the elimination techniques for removing fine bubbles from fine bubble
dispersion in water and how to optimize the elimination procedures to obtain better efficiency.
This document is applicable to fine uncoated bubbles (without shells).
It does not apply to fine coated bubbles (with shells).
NOTE Fine bubbles dispersed in liquid are classified into “fine bubble with shells” and “fine bubble without
shells”. Fine bubble with shells means the fine bubble whose surface/interface is covered almost completely by
an object or a collection of objects.
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 20480-1, Fine bubble technology — General principles for usage and measurement of fine bubbles —
Part 1: Terminology
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20480-1 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/
3.1
fine bubble dispersion
FBD
liquid which contains fine bubbles
[SOURCE: ISO 20298-1:2018, 3.1]
3.2
frequency
number of cycles per second
Note 1 to entry: Expressed in Hertz (Hz).
[SOURCE: ISO 5577:2017, 3.1.1]
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ISO 24261-2:2021(E)

3.3
ultrasonic wave
any acoustic wave having a frequency (3.2) higher than the audible range of the human ear, generally
taken as higher than 20 kHz
4 Requirements
4.1 Sample
Fine bubble dispersions in water that are going to be used to test fine bubble elimination techniques
shall be generated using cleaned fine bubble generating systems with clean water and clean gas such as
air, nitrogen or oxygen.
The purity level of water and gas depends on the sample. The size and concentration indices of fine
bubbles in the sample should be evaluated because fine bubble elimination is one of the evaluating
processes for specified samples. Therefore, the purity level cannot be generally determined as a
measurement condition for evaluations of the elimination efficiency.
The fine bubble dispersion shall not contain stabilizing agents such as surfactants.
If the measurement accuracy of size and concentration indices is very important (for example, in the
case of application to the accreditation of fine bubble business), a water purity level of ISO Grade 1 (see
ISO 3696) is recommended for the water used for generating FBD.
4.2 Measuring instruments
When the measuring instruments are selected for evaluating the potential for fine bubble elimination,
the following requirements for the concentration and the size range shall be considered. These
requirements depend on the characteristics of sample to be evaluated.
1) The total number concentration and total volume concentration of the entire sample including fine
bubbles and contaminants (solid and liquid particles) shall be measured. Water diluent can be used
for diluting the FBD when the concentration is too high for the measurement technique in question.
2) The size range of the entire sample including fine bubbles, contaminants and aggregates of
contaminants shall be measured. Different measuring instruments may be used to confirm the
larger aggregates.
NOTE For example, the particle tracking analysis method can be used for evaluation of number concentration,
and the laser diffraction method can be used for the evaluation of volume concentration. ISO/TR 23015 can be
referred to for details of measurement techniques which can be used for FBD in water.
5 Environment
The air cleanliness should be considered for the measurement to prevent the introduction of impurities.
Ambient temperature and atmospheric pressure should be stable to maintain the stability of ultrafine
bubbles.
Air cleanliness, ambient temperature and atmospheric pressure depend on the local environment and
can vary. However, as they are important settings and can influence the elimination process they should
be recorded prior to any elimination occurring.
If the measurement accuracy of size and concentration indices is very important, (for example, in the
case of application to the accreditation of
...