A DV E RT I S E M E N T F E AT U R E

A DV E RT I S E M E N T F E AT U R E

The buoyancy of bubbles also
depends on their size. Visible
bubbles of gas with diameters
greater than 100 micrometresrise rapidly to the surface of aliquid, while microbubbles rise
more slowly. In contrast, ultrafine
bubbles have a low buoyancy
and can remain suspended inwater for months.
These properties can beused in many applications —for example, in wastewater
processing, the much slower
rise of fine bubbles through‘activated sludge’ means oxygen
transfers to wastewater more
slowly, speeding up sludge
aeration while reducing energyuse; likewise, the slow rise of finebubbles in aquaculture settingsgives more reaction time, and it
has been shown to improve thelevels of dissolved oxygen in awell-stocked indoor shrimp farm.
Scientists and engineers
generate ultrafine bubbles using
hydraulic and electrochemicalsystems to cause liquids tooscillate. Because they areinvisible to the naked eye, it has
been challenging to measureand study ultrafine bubbles,
but new laser diffraction andscattering methods have recently
allowed them to be studied withmore precision.

LESS TOIL AND TROUBLE
WITH TINY BUBBLESULTRAFINE BUBBLES induce new properties that can change how we can use water.

The use of fine bubbles inwastewater treatment could speed
up aeration of sludge and reduceenergy use.

invisible to the naked eye. And
this size difference is reflected in
how they behave.
“Ultrafine bubbles have very
different properties from larger
bubbles,” says Takashi Hata,
a professor at Kochi National
College of Technology in Shikoku,
Japan. In particular, they areneutrally buoyant, can hold alarge electric charge, and can beheld in place by surface tension.
Far from being scientificcuriosities, ultrafine bubbles
have potential for practicalapplications, such as industrial
cleaning, offering manyadvantages. “Using watercontaining ultrafine bubbles
for cleaning could reduce theamount of water needed andalso decrease, or even eliminate,

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detergents and chemicals,”
explains Masateru Hirae,
senior managing director atScience-Co Ltd, an Osaka-based
manufacturer of water purifiers
and ultrafine-bubble products.

FAR FROM BEINGSCIENTIFICCURIOSITIES,ULTRAFINE
BUBBLES HAVEPOTENTIAL
FOR PRACTICALAPPLICATIONSThis has a flow-on effect,
Hirae says, reducing both theenergy used to treat waterand the environmental impactof chemicals. He notes thatultrafine-bubble technology

can contribute to at least
four of the 17 United Nations’Sustainable Development Goals(SDGs), namely SDG 6 (cleanwater and sanitation), SDG 12(responsible consumption andproduction) and SDGs 14 and15 (life below water and life onland, respectively).
THE SCIENCE OF BUBBLESPart of the power of ultrafine
bubbles lies in their highsurface area. “For the same
total bubble volume, ultrafine
bubbles will have a muchgreater total surface area thanlarger bubbles,” explains Hata.
“This greatly increases theirchemical reactivity, physicaladsorption and mass transport
at gas–liquid interfaces.”

Abstract Aerial Art/DigitalVision/Getty

Tiny bubbles of gas — less thana micrometre in size — could
spawn a multi-billion-dollar
industry, by transforming thenormal characteristics of waterand other liquids, making thempotentially useful in diverse
fields, including agriculture,cleaning, hydroponics andwater treatment.
Fine bubbles are classified
into microbubbles (1–100micrometres in diameter) andultrafine bubbles (smaller than
1 micrometre in diameter). Unlike
the bubbles in soda drinks andchampagne, ultrafine bubbles are

AN EXPANDING INDUSTRY
The potential of ultrafine bubbles
for industrial applications isjust beginning to be tapped.
A 2022 report by Research andMarkets, a market researchcompany, predicts that themanufacture and supply ofultrafine bubbles will expand toa multi-billion dollar industry
over the coming decade, withapplications across agriculture,aquaculture, hydroponics andwater treatment.
One area that stands tobenefit significantly fromultrafine bubbles is agriculture.
A hydroponics nutrient solution
containing them accelerated theShower heads that generate fine bubbles could reduce the amount of detergents needed, benefiting theenvironment and consumers.

growth of lettuce seedlings over
two weeks by a factor of 1.41,
while cabbage plants, fish andmice showed improved growth
rates after consuming water
infused with ultrafine bubbles2.
The mechanism has yet to beclarified, but the researchers
speculate that plants and animals
may have more energy available
for growth due to increased
metabolism and less breathing
under hyperoxia conditions.
And including ultrafine bubbles
in water applied to soybean
seedlings suffering stress fromnutrient deficiency improved
their growth3.
Water containing ultrafine
bubbles of ozone is also being
used to clean and sterilize
equipment used for artificial
kidney dialysis4. It has beenshown to have the same
bactericidal effects as thedetergents sodium hypochlorite
and peracetic acid, which are
typically used to clean anddisinfect organic matter. But theozone-containing water does
not suffer from corrosiveness,strong odour and potential
for skin irritation associatedwith those detergents.

Further applications could
emerge following the discovery
that ultrafine bubbles caninhibit the cell growth of certain
bacteria, adding to the utility ofusing ultrafine bubbles of oxygenin wastewater treatment, which
can kill unwanted bacteria at thesame time as improving aeration.
Fine bubbles of ozone can also
be used to kill a pathogenic
fish bacteria in a freshwateraquaculture system5.
And fine bubbles arepromising for domestic uses aswell. Science-Co Ltd has beendeveloping and manufacturingfine-bubble products for
consumers, including bathtubs,
shower heads and taps since2007. “Fine bubbles in waterused for washing can adhere todirt and grime attached to theskin, similar to soap, allowing
users to reduce or eliminate
detergents and disinfectants
that can both irritate skin, andalso add to water pollution,” says
Hirae. Microbubbles in waterused for bathing have also beenshown to remove dead skin.
Taps that generate ultrafine
bubbles may also improvedomestic fabric laundering,

Hirae says, with researchshowing that fine bubbles inwater can enhance the effect ofsurfactants, reducing the amountneeded for washing clothes andpotentially reducing waste waterfrom household laundry.
Ultrafine bubbles not only
have the potential to improve
life on Earth. Scientists at theUniversity of Maine are now
exploring the use of fine bubbles
to enhance life-support functions
on spaceships, such as water
treatment and algae growth.
REFERENCES
1. Park, J.-S. & Kurata, K. Am. Soc.
Hort. Sci. 19, 212–215 (2009).
2. Ebina, K., Shi, K. et al. PLoS One 8,e65339 (2013).
3. Iijima, M., Yamashita, K. et al. Plant
Prod. Sci. 23, 366–373 (2020).
4. Nakahara, Y., Miyazaki, K. et al.
MATEC Web of Conf. 192, 03034(2018).
5. Jhunkeawa, C., Khongcharoen,
N. et al. Aquacult. 534, 736286(2021).

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