ISO/TS 4240-1:2023

Fine bubble technology - Environmental applications - Part 1: Inspection method using online particle counter in dissolved air flotation (DAF) plant

This document specifies the bubble volume concentration and bubble bed depth measurement methods by online particle counter for checking DAF process performance in plant. The test method of bubble volume concentration is made by measuring bubble size distribution in contact zone of DAF tank and calculating using formula. And bubble bed depth is evaluated by measuring the number of bubbles and particles according to the depth at five points in separation zone of DAF tank. This document provides the advantages and limitations of using online particle counter in plant.

Titre manque — Partie 1: Titre manque

General Information

• Status: Published
• Publication Date: 30-Mar-2023
• ICS: 07.030 - Physics. Chemistry
• Technical Committee: ISO/TC 281 - Fine bubble technology
• Drafting Committee: ISO/TC 281/WG 3 - Applications of fine bubble technology
• Current Stage: 6060 - International Standard published
• Start Date: 31-Mar-2023
• Due Date: 21-Dec-2023
• Completion Date: 31-Mar-2023

Overview

ISO/TS 4240-1:2023 - "Fine bubble technology - Environmental applications - Part 1: Inspection method using online particle counter in dissolved air flotation (DAF) plant" specifies indirect, on-site inspection methods to evaluate bubble performance in DAF systems. The Technical Specification defines how to measure bubble volume concentration (BVC) and bubble bed depth using an online particle counter and describes the method principle, test equipment, procedures, and practical advantages and limitations for plant-scale monitoring.

Key topics and requirements

• Objective: Provide plant-level methods to monitor BVC and bubble bed depth in full-scale DAF plants where direct observation or displacement tests are impractical.
• Measurement principle: Use a particle counting method (PCM) to obtain bubble size distribution (typical detection range ~10 µm to 100 µm) and calculate BVC from measured counts and median bubble volumes using the specified formula.
• BVC procedure:
  • Portable online particle counter (10–100 µm) and metering pump (≈100–200 L/min).
  • Sampling from the contact zone (mid-depth, ~1 m from sidewall) for ~5 ± 1 minutes.
  • Draw bubble size distribution, compute BVC from counts and sampled volume.
• Bubble bed depth procedure:
  • Sample at five horizontal points across the separation zone (inlet, outlet and three evenly spaced points).
  • Use a scaled pole and sampling hose to take depth-profile measurements at consistent intervals.
  • Identify the bubble-bed interface where counts change abruptly; report depth per point and take the minimum as plant bubble bed depth.
• Equipment and sampling considerations: portable particle counter, stable metering pump (100 L/min for depth profiling), sufficient tubing length (Annex G covers sampling-tube effects).
• Documentation: Annexes provide PCM details, visual comparison tests, full-scale examples, operating-condition effects and particle/bubble contribution analysis.

Applications and who uses it

• Primary application: On-site performance inspection and real-time monitoring of dissolved air flotation (DAF) units in water and wastewater treatment.
• Users:
  • Plant operators and process engineers seeking routine verification of microbubble performance.
  • Commissioning engineers and consultants performing troubleshooting or optimization of DAF performance.
  • Researchers and pilot-plant teams comparing laboratory results with full-scale operation.
• Value: Enables portable, rapid trend monitoring of BVC and bubble-interface depth where direct measurement is not practical; supports operational decisions on recycle ratio, pressure and generator performance.

Advantages & limitations (summary)

• Advantages: Portable, online monitoring; effective for trend detection and full-scale inspection; short measurement times and straightforward equipment.
• Limitations: Indirect method (not as absolute as water-displacement BVC); accuracy depends on particle counter range, sampling tube length and stable operating conditions (detailed in Annexes).

Related standards

• ISO 20480-4 - Fine bubble technology: terminology related to microbubble beds.
• Other parts of the ISO 4240 series (see ISO website for the complete list).

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 4240-1
First edition
2023-03
Fine bubble technology —
Environmental applications —
Part 1:
Inspection method using online
particle counter in dissolved air
flotation (DAF) plant
Reference number
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 BVC measurement technique . 2
5.1 Test equipment . 2
5.2 Procedure . 3
6 Bubble bed depth measurement technique . 4
6.1 Test equipment . 4
6.2 Procedure . 5
7 Advantages and limitations . 6
7.1 Advantages . . 6
7.2 Limitations . 7
Annex A (informative) Measurement of bubble size and size distribution by PCM .8
Annex B (informative) Height from the water surface to the bubble bed depth .9
Annex C (informative) Comparison of the results of bubble bed depth obtained by using the
naked eye and by using a particle counting method .10
Annex D (informative) Measuring bubble bed depth of DAF process in full scale .12
Annex E (informative) Change of bubble bed depth at different operating conditions .14
Annex F (informative) Contribution of particles and bubbles in particle count
measurements .15
Annex G (informative) Effect of sampling tube length .17
Bibliography .18
iii
Foreword
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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 4240 series can be found on the ISO website.
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iv
Introduction
The dissolved air flotation process is widely used for water treatment plant. This process used micro
bubbles to remove particles by floating them on the surface. There are various factors to check the
operation of the DAF plant. Many of these factors can be measured in field scale DAF plant. However,
some factors are very difficult to measure in the field.
One of these factors is bubble volume concentration (BVC). BVC is usually used as index of the number
of bubbles. Generally, BVC is evaluated by the water displacement method. This method measures the
volume of bubbles as the volume of water displaced. The water displacement method is a direct way
to give accurate BVC of bubble water. However, this method needs large equipment depending on the
capacity of the bubble generator. So, it is almost impossible to measure BVC directly from the DAF plant.
Lab and pilot test with the same nozzle of DAF plant and predictions based on the test results are most
widely used.
Bubble bed depth is also difficult to measure in DAF plant. It is easy to observe the creation of a bubble
bed interface in the middle part of the reactor by the naked eye in a lab and pilot scale DAF reactor
manufactured with a transparent wall. Although it is not possible to present the interface by a single
straight line, a bubble interface zone exists in which above the interface there are clouds of bubbles and
below the interface almost no bubbles are observed. The centre of the bubble interface zone is defined
as the bubble bed interface. Bubble bed depth is defined by the height from the water surface to the
bubble bed interface as presented in Figure A.1. However, in a full-scale DAF plant, it is not easy to
locate the bubble bed interface. The difficulty is that observation by the naked eye is not possible due to
structural constraints.
Therefore, this document specifies indirect measurement methods of BVC and bubble bed depth. This
approach can be useful for on-site inspection of DAF plant.
v
TECHNICAL SPECIFICATION ISO/TS 4240-1:2023(E)
Fine bubble technology — Environmental applications —
Part 1:
Inspection method using online particle counter in
dissolved air flotation (DAF) plant
1 Scope
This document specifies the bubble volume concentration and bubble bed depth measurement methods
by online particle counter for checking DAF process performance in plant.
The test method of bubble volume concentration is made by measuring bubble size distribution
in contact zone of DAF tank and calculating using formula. And bubble bed depth is evaluated by
measuring the number of bubbles and particles according to the depth at five points in separation zone
of DAF tank.
This document provides the advantages and limitations of using online particle counter in plant.
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 20480-4, Fine bubble technology — General principles for usage and measurement of fine bubbles —
Part 4: Terminology related to microbubble beds
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20480-4 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
bubble volume concentration
BVC
index of the volume of bubbles contained in the unit volume of water
Note 1 to entry: It is calculated by the ratio of the total bubble volume to the volume of generated bubble water
during any given time, expressed in %.
[SOURCE: ISO 20480-4:2021, 3.16, modified — "index" has been removed from the term.]
3.2
particle counting method
indirect method to count the number of bubbles and its size distribution in a measurement
Note 1 to entry: Particle counting method (PCM) can trace the variation tendency of the BVC index.
Note 2 to entry: Effective range of particle counter to measure bubble size is from 1 μm to 100 μm.
Note 3 to entry: The sampling flowrate is normally adjusted, and the numbers of bubble are counted in the
applied volume of sample.
3.3
bubble and particle size distribution
range (minimum to maximum) of bubble and particle size in a measurement
4 Principle
A particle counter is an instrument which is widely used for the determination of bubble size
[1]-[4]
distribution (see Annex A) . Based on this characteristic, it can be used to evaluate BVC in DAF
plant. Even though the result of this method is not accurate, it can be used to show the tendency of BVC
according to time by real-time monitoring in DAF plant.
5 BVC measurement technique
5.1 Test equipment
This document aimed to evaluate BVC in DAF plant. Therefore, test equipment should be easy to move.
Figure 1 shows the example of equipment for BVC evaluation. The list of equipment is shown below.
a) Online particle counter:
— detecting range: approximately 10 μm to 100 μm;
— support online-mode;
— portable.
b) Metering pump which can be operated at flowrate approximately 100 l/min to 200 l/min.
c) Tube of sufficient length (the effect of sampling tube length is shown in Annex G).
Key
1 online particle counter
2 pump
3 tube
4 flocculation basin
5 contact zone
6 separation zone
Figure 1 — Schematic diagram of equipment for BVC evaluation
5.2 Procedure
a) To minimize errors caused by particles entering the DAF tank, the inflow valve is locked in the DAF
tank to prevent entry of untreated water. In this state, the bubble generator is operated to remove
residual particles in the DAF tank and to make a stable state.
b) The test equipment should be installed near the contact zone for evaluating BVC. The sample is
taken in the middle of the point at the contact zone of the inlet and the outlet. Sampling depth is
at half the depth of the contact zone. Tube for sampling is installed 1 m away from the sidewall to
prevent from interruption of sidewall. Metering pump flowrate shall be approximately 100 l/min to
200 l/min to minimize the influence on the DAF bubble bed.
c) The bubble size distribution is measured using online particle counter. The measurement time
shall be 5 ± 1 min to obtain stable data.
d) Based on the measurement results, the bubble size distribution graph shall be drawn. The
horizontal axis represents the bubble size range, and the vertical axis represents the number of
bubbles. The example is shown in Figure A.1.
e) Calculate BVC using Formula (1).
*
∑×ni
*
i
BVC= ×100 (1)
Q
where
BVC
is the bubble volume concentration in %;
*
is the volume of median size bubble of a certain range in ml;
i
*
n
* is the number of bubbles of a certain range whose median size bubble volume is i ;
i
Q
is the volume of sampled water from the contact zone in ml.
6 Bubble bed depth measurement technique
In the case of laboratory and pilot test, bubble bed depth can be measured with the naked eye by
making DAF tank of transparent wall. However, it is impossible in DAF plant. This document provides
the measurement method of bubble bed depth based on particle counting method. The accuracy of
particle counting method was verified in Annex C through the experiments in pilot plant.
6.1 Test equipment
This document aimed to measure bubble bed depth in plant. Therefore, test equipment should be easy
to move. Figure 2 shows the typical example of equipment for bubble bed depth measurement. The list
of equipment is shown below.
a) Online particle counter:
— detecting range: approximately 10 μm to 100 μm;
— support online-mode;
— portable.
b) Metering pump which can be operated at flowrate 100 l/min stably.
c) Tube of sufficient length from the bottom of DAF tank to online particle counter.
d) Scaled pole with sufficient length for marking the position of the hose.
Key
1 online particle counter
2 pump
3 tube
4 flocculation basin
5 contact zone
6 separation zone
7 scaled pole
Figure 2 — Schematic diagram of equipment for bubble bed depth measurement
6.2 Procedure
a) In order to determine the horizontal profile, five points are selected as investigating point. They
are inflow and outflow points of separate zone and three more points with equal interval between
them.
b) At each point, bubble and particle size distribution is investigated using
...