Introduction to Ultra Fine Bubble TechnologyFine bubble technologies offer performance enhancement in a number of processes and applications suc...
Published on by Heindre Rademan, Managing Partner at ClaasECO
Fine bubble technologies offer performance enhancement in a number of processes and applications such as cleaning, aquaculture and agriculture.
Characterization of ultrafine bubbles is critical to the further development of industrial applications. A number of characteristics such as bubble size, bubble number stability, bubble number concentration as well as other physical and chemical characteristics are important in such applications. In order to provide a verifiable characterization platform for these applications, a set of sampling and sample preparation procedures has been developed. This approach results in the most reliable correlation between the characteristics of the fine bubbles in dispersion and their application effectiveness.
It is commonly accepted that the sample preparation technique will depend on the characterization technique used. For this reason it is recommended that the "ISO 20298-1:2018(en)
Fine bubble technology — Sampling and sample preparation for measurement — Part 1: Ultrafine bubble dispersion in water" be consulted. This document is applicable to relatively stable dispersions where the size and number of bubbles are relatively constant for the duration of the sampling, sample preparation and measurement. It must be noted that this document is not applicable to less stable fine bubble dispersions or microbubble dispersions.
Applications of fine bubble technologies can be found in cleaning, environmental improvement, the food and drink sector, aeration systems, medicine, water and waste water treatment, as well as agriculture and aquaculture. Developing appropriate terminology for such diverse technologies is therefore critical to business trade or product acceptance by consumers.
Fine bubbles can be present in both liquids and solids. Fine bubbles can contain air or another gas. The bubble can be held in place by surface tension or be surrounded with a coating, e.g. a lipid. Fine bubbles generated for various applications can vary in size, gas content or bubble coating. The generation techniques used are also different.
It should be noted that the motion of bubbles in a medium can be determined by buoyancy forces or randomly and thermally activated processes leading to Brownian motion. For this reason, larger bubbles can display buoyant behaviour (rise upwards) and smaller bubbles remain in the liquid medium displaying random motion. The document "ISO 20480-1:2017(en)
Fine bubble technology — General principles for usage and measurement of fine bubbles — Part 1: Terminology" focuses on the definitions of such entities. This document specifies terminology and definitions used in the area of fine bubble technology. Terminology in this document covers general principles, measurements, and individual applications of fine bubble technology.
Below some of the VERY IMPORTANT TERMS AND CONDITIONS the users of the technology should take note of.
Figure 1 - Scale diagram showing bubble sizes
bubble - gas in a medium enclosed by an interface
fine bubble - bubble with a volume equivalent diameter of less than 100 μm
Note 1 to entry: 100 μm is also represented as 1 × 10−4 m.
Note 2 to entry: Annex A provides further information on the use of terms “fine bubble” or “ultrafine bubble”, instead of “nanobubble”.
ultrafine bubble - fine bubble with a volume equivalent diameter of less than 1 μm
Note 1 to entry: Measured examples of ultrafine bubbles in water by particle characterization methods, in practical application fields, mostly range between 100 nm and 200 nm. The measured results can include contaminants, as well as ultrafine bubbles.
microbubble - fine bubble with a volume equivalent diameter in the range from equal or greater than 1 μm to less than 100 μm
Note 1 to entry: Figure 1 shows the size range of bubbles, fine bubbles, ultrafine bubbles, and microbubbles.
Key
1 bubble
2 fine bubble
3 ultrafine bubble
4 microbubble
solid medium - material in solid phase in which bubbles are dispersed
Note 1 to entry: A solid medium can be a congealed or chemically immobilized (solidified) liquid which contains bubbles. As a result, bubbles are immobilized or have a restricted degree of mobility.
liquid medium - material in liquid phase in which the bubbles are dispersed
bubble number concentration - number of bubbles per unit volume of medium
Note 1 to entry: The medium can be solid medium or liquid medium.
volume equivalent diameter - deq
diameter of the spherical bubble of equivalent volume
bubble volume - spherical (or otherwise) volume of a bubble
Note 1 to entry: In case of a bubble covered by its bubble shell (3.10), the volume of the bubble shell should be included.
bubble shell - object or a collection of objects that cover the bubble surface almost completely
bubble temperature - temperature at which an infinitesimal amount of vapour is in equilibrium with a bulk liquid for a specified pressure [SOURCE: ISO 20765‑2:2015, 3.2, modified — Note 1 to entry and Note 2 to entry have been deleted.]
bubble-point pressure - pressure under which gas bubbles form in a liquid at a particular operating temperature which gas bubbles form [SOURCE: ISO 15156‑2:2015, 3.2]
coalescence - action by which bubbles in suspension unite to form larger bubbles [SOURCE: ISO 29464:2011, 3.1.24, modified — “liquid particle” has been changed to “bubbles”.]
bubble stability - duration for total volume of bubbles in dispersion to increase twofold or reduce by half under a given temperature and pressure conditions
bubble size stability - duration for a volume equivalent diameter of a bubble to increase twofold or reduce by half under given temperature and pressure conditions
bubble number stability - duration for the number of bubbles to increase twofold or reduce by half under a given temperature and pressure conditions
bubble generating system - system for creating bubbles in a liquid medium
fine bubble generating system - system for creating fine bubbles in a liquid medium
ultrafine bubble generating system - system for creating ultrafine bubbles in a liquid medium
number concentration index - quantity representing the concentration of objects in a fine bubble dispersion measured by an industrially available and agreed method
Note 1 to entry: Fine bubble dispersion in reality often contains not only fine bubbles but also other components with application-specific functions.
size index - quantity representing an object size in a fine bubble dispersion measured by an industrially available and agreed method
Note 1 to entry: Fine bubble dispersion in reality often contains not only fine bubbles but also other components with application-specific functions.
In recent years, readily available measurement techniques of bubbles have made it possible to characterize microbubbles and ultrafine bubbles. Such techniques have shown that ultrafine bubbles can almost remain as they are for a number of months.
Fine bubble technologies are very new, and their applications are useful in a number of fields today. Developing appropriate terminology for such a diverse area of technology is therefore critical to business trade or product acceptance, in view of the wide range of users of fine bubbles.
For better communication among the users of fine bubbles, the document "ISO 20480-2:2018(en) Fine bubble technology — General principles for usage and measurement of fine bubbles — Part 2: Categorization of the attributes of fine bubbles" introduces the quality criteria of a medium such as water, as well as two indices, one for size and the other for number concentration. This document also provides an explanation for classifying fine bubbles by dimensional characteristics and by rise velocity.
It should be noted that the motion of bubbles in a medium can be determined by buoyancy forces or randomly and thermally activated processes leading to Brownian motion. For this reason, larger bubbles can display buoyant behaviour (rise upwards) and smaller bubbles remain in the liquid medium displaying random motion. The ISO 20480-2:2018 establishes the general principles and descriptors to allow users to describe the quality of the liquid media and the size and concentration of fine bubbles. It is also intended to allow users to classify fine bubbles by rise velocity.
Fine bubble technology applications have grown steadily in recent years. They now embrace a diverse range of industrial activities from enhancing the growth rates of plants in agriculture to the separation peel-off of solar panel silicon wafers in semiconductor manufacturing process.
Improved advanced cleaning purification of waste water and enhanced high throughput removal of lubricant oil on machined works and of salt stains from a surface of traffic infrastructures, have also been demonstrated.
Most of these applications are currently limited to the site where the generating system of fine bubble water is installed close to the application objects and operated simultaneously to the application. Expansion for applications where the site of bubble application is different from that of generation is being implemented by some innovative industries, but there are currently no concrete guidelines for storage and transportation of fine bubble water, as typical ultrafine bubbles (UFB) are known to have high stability once generated. The purpose of the document "ISO 21255:2018(en) Fine bubble technology — Storage and transportation of ultrafine bubble dispersion in water" , is to expand the scope of application of initial measurements of fine bubble quality downstream in the supply chain. This document specifies the requirements related to the planning, equipment and operation process necessary to store and transport ultrafine bubble dispersions without significant deterioration in terms of number concentration index. This document is intended to help assessing the acceptable conditions and periods for storage and transportation that guarantee integrity of ultrafine bubble quality. It also describes the procedures and equipment for storage and transportation of ultrafine bubble dispersions in water and specifies the related requirements in order to maintain such bubble characteristics as size and number concentration.
Salt and materials derived from other pollution sources are known to coat surfaces of exterior of steel structures over time. Highway bridges and other steel structures are particularly vulnerable to anti icing salts or ocean spray. It is necessary that this contamination be removed in order to prevent growth of corrosion and to preserve the life time of the structure. Maintenance is conducted at times of inspection, possibly via the erection of suitable scaffolding and platforms and therefore a rapid efficient cleaning mechanism is essential.
High-pressure water sprays are commonly used for the cleaning method due to their hydrodynamic power. The method requires the operator long term engagement to dangerous operation in inhospitable environment.
It has been shown recently that cleaning process is much more effective and quicker once the water used for the high-pressure spray is augmented with the addition of ultrafine bubbles (UFB) and that markets of ultrafine bubble water or its generating systems are growing rapidly.
The document "ISO/TS 21256-1:2020(en)Fine bubble technology — Cleaning applications — Part 1: Test method for cleaning salt (NaCl)-stained surfaces" intend to provide users of such products and systems with objective information on the cleaning performance of ultrafine bubble water and to facilitate the improvement of ultrafine bubble waters and their generating systems.
The test procedure correlates the ultrafine bubble enhanced performance with the presence of ultrafine bubbles under standardized conditions based on the most commonly used criteria such as hydrodynamic characteristics of high-pressure water spray, quality of raw water before mixing with ultrafine bubbles, quality of salt stain, quality and dimension of coating and substrate of test steel material and testing environmental conditions. In this document, the presence of ultrafine bubbles is evaluated by measuring their sizes and number concentrations. The performance of the method is assessed by measuring the change in removal of salt from the test sample surface due to application of the ultrafine bubble water relative to that of plain water as control. Example application of the test procedure will demonstrates the test results on various steel bridges long exposed to environments of express ways.
Mineral oil is used in manufacturing processes of industrial products, for applications such as cutting, lubrication and cooling. Oil remaining on the surface of products has to be cleaned during operation and at the end of the process. The main cleaning solvent fluids used in these industries are solvent based (e.g. hydrocarbon detergent liquids, bromine-containing detergents, and alkali detergents), despite it being well known that such detergents can cause environmental pollution such as ozone layer depletion, water pollution, etc.
As an ecological alternative, fine bubble technology, which does not use detergents, is becoming popular. Use of fine bubble technology improves resource sustainability, energy saving and safety, as it uses less water and no chemical substances.
The document "ISO 21256-2:2020(en) Fine bubble technology — Cleaning applications — Part 2: Test method for cleaning machine-oil stained surfaces of machined metal parts", provide a procedure that can help demonstrating the cleaning performance of such technology, so that different methodologies can be compared.
Recent development in the fine bubble technology expands its market, such as cleaning, water treatment, agriculture and aquaculture as well as biomedical. Above all, the application of microbubble technology accelerates the market penetration.
Many measurement technologies have been historically developed to assess the characteristics of microbubbles and are now used in various application fields. However, the dynamic nature of microbubbles makes it hard for the users to report their measurement results with confidence. The low stability of microbubbles that includes shrinking, deformation, coalescence and dissolution of individual microbubble can require a specific sampling procedure and short measurement time.
The document "ISO 21910-1:2020(en) Fine bubble technology — Characterization of microbubbles — Part 1: Off-line evaluation of size index" specify an evaluation method for size index of microbubbles in water to be used in a measurement laboratory. The application of the document to measurement system will yield comparable results over an application field, as far as the specified types of measuring instruments are equipped and the specified sampling procedures are met. Since the comparability relevance depends on the sampling procedures and the measurement environments, each measurement can require relevant descriptions. It must be noted that the evaluation method is only applicable to microbubbles with or without shell in water within the range from 1 μm to 100 μm. It describes the sampling methods from the point generating or dispersing microbubbles in the retention container to the detecting point of the measuring instruments.
The recent progress in the application of fine bubble technology exhibits successes in the various technical fields such as environmental technology in water and washing and cleaning technology for mechanical engineering. The applications for agro- and aqua- farming and food industrial field also draw high interests of markets in view of fine bubble enabled performance in enhancing growth of agro- and aqua- products, improving their quality, saving resources for farming and ensuring safety of the food products. Various industries engaged in such products are introducing the fine bubbles to their farming field by applying fine bubble generating systems, eventually creating new market for the generating systems.
However, since technology transfer from fine bubble technology to technology fields of agro- and aqua-farming and food industries is not well supported by common understanding of the fine bubbles or their generating technology, results of evaluation on fine bubble enhanced performance cannot be accepted commonly by both generating system suppliers and its users at the transaction scene. Furthermore, a variety of agro- and aqua- farming products makes it difficult to adopt a systematic approach for selection and application of generating systems. (Agro farming is the advance form of traditional Agriculture,basically it is a skill of cultivating plants and livestock.)
The performance evaluation based on objective evidence resulting from standardized procedures is intended to bridge the two technologies and facilitate diverse fields of applications for fine bubble technology in the global market. In order to accelerate sound global market formation, development of test procedures is urgently demanded by both technology stakeholders.
The document "ISO/TS 23016-1:2019(en) Fine bubble technology — Agricultural applications — Part 1: Test method for evaluating the growth promotion of hydroponically grown lettuce" intends to meet these needs by specifying the test procedure to be applied to the generating system for agro- and aqua- farming and food industries uses. The evaluation is made by applying fine bubble water generated by the object system to lettuce and by measuring its growth. The product, lettuce, is globally accepted and the yielded test data represents the performance of the tested system over other products in such major product family as, for example, leaf vegetable. The growth process of lettuce is much simpler than other vegetables making the measuring process much easier in the test procedure. The specified test conditions, namely the environment for growth, are also easy to be controlled allowing many testing plants globally available. The parameter measured is the change in the harvested mass of lettuces with application of fine bubbles compared to that without application in a specified period of growth. This document specifies a test method for evaluating the effect of fine bubble water on the growth promotion of hydroponically grown lettuce by estimating the incremental gain in mass of the stems and leaves over a specified growth period.
Considering the increasing use of fine bubble technology in agriculture, the document "ISO 23016-2:2019(en) Fine bubble technology — Agricultural applications — Part 2: Test method for evaluating the promotion of the germination of barley seeds" has been developed to establish standards in this area, with particular focus on promoting the germination and growth of barley seeds.
The use of fine bubble technology in agriculture has been confirmed to benefit various types of agricultural products and has attracted the interest of various countries. Application of the technology to leafy vegetables in agriculture is already well-established, and this is being expanded to seed germination and growth as well. Worldwide as well, standardization of fine bubble technology in the field of agriculture is not only being spotlighted but is being conducted in practice at a rapid pace. The technology is expected to blossom rapidly.
Fine bubble technology has been applied successfully not only in agriculture but also in the fields of environmental science, food, marine products, medicine, etc. Wide-ranging progress in standardizing the technology is being made in these fields. The achievement of standardization in various fields is expected to result in increased worldwide recognition of fine bubble technology in the future. The ISO 23016-2:2019 specifies a method to test the promotion of the germination of barley seeds, using ultrafine bubble (UFB) water produced from an ultrafine bubble water generating system. The performance of the method is assessed by measuring the ratio of barley seed germination.