Nanobubbles (NBs) or ultrafine bubbles are sub-micron (~50nm to ~700nm) gas-containing cavities in aqueous solution with unique physical characteristics that differ from other types of bubbles and have the ability to change the normal characteristics of water. The electrolysis of aqueous solutions produces solutions that are supersaturated in oxygen and hydrogen gas. This results in the formation of gas bubbles, including nanobubbles ∼100 nm in size that are stable for ∼24 h. Their use drastically improves the efficiency of gas to liquid systems and processes. Over the last few years NBs have been scaled up for applications at an industrial level.
Properties
Properties of NBs include:
- Longevity.
- Negative surface charge.
- Low buoyancy.
- High gas solubility.
- Capability to generate free radicals.
- Sterilization capability through bactericidal action.
- Removal of contamination without the need for cleaning agents.
- Bio-activation in cells.
- Growth promotion for fish, crustacea and plants.
- Cell protection.
- Heat transfer capabilities to raise or lower the temperature of a liquid rapidly and effectively.
- Vaporization promotion capability for water-cooled cooling towers and evaporation-based desalination systems.
- Can halt concrete and metal decay.
Applications
Their use is transformative for environmental, food and wastewater treatment industries and they also find application in:
- Water purification/sterilization (various industries).
- Cooling tower de-scaling.
- Environmental purification and remediation.
- Medical cleaning applications (sanitization and bacteria control).
- Drug delivery.
- Animal farming-drinking water enrichment (reduces bacterial growth).
- Agriculture and food production (reduction in use of chemicals).
- Aquaculture-oxygenation of fish and aquaculture dams.
- Mining-acid water treatment.
- Oil and gas Industry – oil spill clean-up and storage tanks.
NBs have been increasingly used in environmental markets over the last decade in:
- mineral froth flotation
- membrane defouling
- water disinfection
- sediment remediation.
The use of NBs can significantly improve the efficiency of contaminant removal, downsizing treatment facilities, and reducing operation times and costs in environmental engineering.
Definition
Microbubbles sit in the range of fine bubbles, and nanobubbles are part of the range of ultra-fine bubbles. Ultra-fine bubbles (UFB’s), on the other hand, are defined by the International Organization for Standardization, under ISO/TC 281 as:
- Microbubbles: Greater than 1 and Less than 100 μm
- Fine bubble: Less than 100 μm
- Ultrafine (nano) bubbles: Less than 1 μm, normally between 100 and 200 nm
Other definitions include NBs as ultrafine bubbles with a diameter ranging from 1 to 1000 nm, whereas micro- and macro bubbles have respective diameters of 10–50 μm or above.
Nanobubbles can exist on surfaces (surface or interfacial NBs) and as dispersed in a liquid phase (bulk NBs). They have been characterized by various techniques, such as AFM, spectroscopic methods, rapid cryofixation/freeze fracture, quartz crystal microbalance, neutron reflectometry, and X-ray reflectivity.
Various methods have been established for the preparation of nanobubbles including solvent-exchange, temperature gradient, microwave, pressure reduction, and electrochemical methods. The most widely-used method to produce surface nanobubbles. A hydrophobic substrate is first contacted with water which is then replaced by ethanol. At this stage, no nanobubbles can be observed. After the ethanol is replaced by water, nanoscale bubbles covering the substrate surface can be found. Other organic solvents, such as methanol and 2-propanol,can also be used and Other exchange processes such as exchanging cold water against warm water and ethanol solution against salt solution have been deployed. Solvent exchange process can also be applied to produce interfacial nanodroplets.
Nanobubble equipment manufacturers
There are numerous commercial NB generators on the market for both laboratory and pilot-scales. The main commercial market for NBs is in Japan, where manufacturers collaborate with large corporations and research institutes.
acniti LLC
Japan
www.acniti.com
The company is a manufacturer of nanobubble equipment and industrial oxygen concentrators. They produce the Turbiti ozone land-based nanobubble mixer.
Figure 1: Acniti nanobubble mixer.
Anzai Kantetsu Co. Ltd.
Japan
http://anzaimcs.com/
The company has developed oxygenated nanobubble technology based on patented carbon ceramic nanopore technology. With this method a vapor phase is formed via venting through nano-level ultrafine pores, and then a liquid flow over the ultrafine pores boundary that precisely ends the vapor phase. This then results in the generation of ultrafine bubbles. The company has registered patents in Japan, the US (no 8,919,747 B2) and Europe for his carbon ceramic technology and is regarded as the technology market leader in Japan.
AquaB Nanobubble Innovations Ltd.
Ireland
http://www.aqua-bubble.com/
The company is a spin-out from the University College Dublin to commercialise a new energy-efficient method to generate and release substantial volumes of metastable, nano-scale gas bubbles in water. This method is based on research carried out by Professor Niall English and Dr Mohammad Reza Ghaani at UCD’s School of Chemical and Bioprocess Engineering, who are the co-founders of AquaB.
EnH Co., Ltd.
Korea
http://www.enh-nano.com/
The company is a spin-out from Dankook University and has developed a Nano Bubble production technology based on a proprietary self-arrangement technology with improved gas solubility and dispersion. The company uses a Fluid-mobile Pressurized dissolution method to generate NBs.
Fawoo Engineering
Korea
www.fawooeng.com
Fawoo Engineering develops and supplies the Fawoo Nanobubble Generator, based on patented technology. Fawoo Nanotech has patented technologies related to mixers and tubes, which are key technologies that generate nanobubbles. Nanobubble generating devices were developed by using patented technology and are used to purify water quality in agriculture and sewage.
GreenTech California (GTC)
USA
https://greentechcalifornia.us/
Start-up developing nanobubble technology based on research from at the University of California, Irvine (UCI). The company has a partnership with BDP EnviroTech. The company has a global utility patent for its nanobubble technology.
GTC applies nanobubbles to water treatment plants using fine filters and RO (Reverse Osmosis). The Nanobubble Generator, attaches to part of a water purification system, like a pipe, and utilizes the movement of water to produce enough nanobubbles for filtration. Membrane fouling by scale forming salts (primarily carbonates, bicarbonates and sulfates of calcium and magnesium) are significantly reduced and RO operated without adding antiscalant chemicals.
Moleaer, Inc.
USA
https://www.moleaer.com/nanobubbles/
Moleaer™ develops industrial scale nanobubble systems. The company has deployed nanobubble generators at more than 450 customer sites worldwide since 2016.
NAC Co., Ltd.
Japan
http://www.foamest.shop/
The company manufactures and sells micro/nano bubble generators and is also involved in parts processing, welding processing, cutting processing, assembly, jigs and tools, industrial machine design, development and manufacturing of machine tool and spacecraft related parts. The company’s micro-nano bubble generators are developed using a polymer film processing technology-original polymer film is processed physically and nano porous structures are made in the film.
Figure 2. Foamest column series.
Further information
Nanobubbles (Ultrafine bubbles): Applications, markets and companies
Published Novermber 2020, available at https://www.futuremarketsinc.com/nanobubbles-ultrafine-bubbles-applications-markets-and-companies/
