ISO 24261-1:2026

International
Standard
ISO 24261-1
Second edition
Fine bubble technology —
2026-11
Elimination method for sample
characterization —
Part 1:
Evaluation procedure
Technologie des fines bulles — Méthode d'élimination pour la
caractérisation de l'échantillon —
Partie 1: Mode opératoire d'évaluation
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 1
4.1 Sample .1
4.2 Measuring instruments .2
5 Environment . 2
6 Evaluation of fine bubble elimination efficiency . 2
6.1 General .2
6.2 Reduction rate .2
6.3 Confirmation of contaminants aggregation .3
6.4 Evaluation procedure of fine bubble elimination .3
7 Test report . 4
7.1 Report of the testing results.4
7.2 Report of the testing conditions .4
Annex A (informative) Simulations of fine bubble elimination process . 5
Annex B (informative) Decrease of concentration caused by fine bubble elimination and
aggregation . 7
Bibliography . 9

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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This document was prepared by Technical Committee ISO/TC 281 Fine bubble technology.
This second edition cancels and replaces the first edition (ISO 24261-1:2020), of which it constitutes a minor
revision.
The changes are as follows:
— in 7.1, the following list item was added "f)  Number of this document";
— in Figure A.1 and Figure A.2, the unit "million/ml" was revised to "×10⁶ particles/ml".
A list of all parts in the ISO 24261 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.

iv
Introduction
Fine bubble technology has recently seen growth in its application to markets in cleaning, water treatment,
agriculture, and aquaculture as well as biomedical fields. Now, methods are required to evaluate the
generation systems. Characteristics like number concentration index and the size index of fine bubbles are
especially indispensable for those evaluations.
Furthermore, fine bubble dispersion water may contain other solid and liquid particles. Due to this concern,
it may be impossible to evaluate the characteristics of fine bubbles. Therefore, a method to address the
presence of other particles is urgently needed.
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.
This issue can be resolved, using the phenomenon by which the bubbles can be eliminated without any
residues after dissolution and flotation. If a method that eliminates fine bubbles in specific size range is
known, it is possible to distinguish fine bubbles from other solid and liquid particles. The eliminated particles
can be fine bubbles. A solution in which fine bubbles are not present or have been almost completely removed
can be used as a blank solution for background measurements. Standardizing elimination techniques and
evaluation methods are required as fine bubble elimination techniques will continue to develop further.
This document is intended to specify the evaluation method for elimination efficiency of fine bubbles from
fine bubble dispersions in water.
A standard method to evaluate fine bubble elimination efficiency enables easy and clear comparison among
several techniques and presents optimal conditions for respective elimination techniques.

v
International Standard ISO 24261-1:2026(en)
Fine bubble technology — Elimination method for sample
characterization —
Part 1:
Evaluation procedure
1 Scope
This document specifies the evaluation procedure of fine bubble elimination for fine bubble dispersion in
water. This document is applicable only to fine bubbles without shell.
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 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
elimination of fine bubbles
process for the decrease of concentration index of fine bubbles
3.2
fine bubble dispersion
FBD
liquid which contains fine bubbles
[SOURCE: ISO 20298-1:2018, 3.1]
4 Requirements
4.1 Sample
The fine bubble dispersion to be evaluated shall be generated by cleaned fine bubble generating systems
using pure water and pure gas such as air, nitrogen and oxygen.
The purity level of water and gas depends on the sample whose size and concentration indices of fine
bubbles should be evaluated because fine bubble elimination is one of the evaluating process for specified

samples. So, the purity level cannot be generally determined as measurement condition for evaluations of
the elimination efficiency.
The fine bubble dispersion shall not contain stabilizing agents.
If the measurement accuracy of size and concentration indices is very important (e.g. for accreditation
purposes), a water purity level of Grade 1 according to ISO 3696 is recommended for the water used for
generation of FBD.
4.2 Measuring instruments
When the measuring instruments are selected for evaluating fine bubble elimination for FBD in water
the following parameters about concentration and size range shall be confirmed, which depends on the
characteristics of the sample to be evaluated:
a) Total number concentration and/or total volume concentration including fine bubbles and contaminants
such as solid particles and liquid particles can be measured. Water diluent can be used for diluting the
FBD in water when the concentration is over the measuring range.
b) Total size range including fine bubb
...