Watched this on NHK some time last week. Bubbles contained in a liquid are visible to the eyes when the bubble sizes are large enough to see, as we can see bubbles in carbonated drinks or those coming from the air diffuser in a water tank. Bubbles with the size of a few millimeters in diameter show visible surfacing action in a liquid, and the presence of fine bubbles of dozens of microns in diameter can be confirmed with white turbidity in a liquid, because these bubbles are scattering substances.
Bubbles in diameter smaller than the wavelength of light are called ultrafine bubbles, and they are too small to see. Ultrafine bubbles measure just one-billionth of a meter in diameter and have many other remarkable features that ordinary bubbles do not possess. For example, these bubbles can stay in a liquid for a long time, and are electrically charged, and are extra highly pressured as well. These special features of ultrafine bubbles have attracted attention from many industries such as food, cosmetics, chemical, medical, semi-conductor, and agriculture. They have the ability to extend the freshness of raw fish, and promote crop growth. In the medical field, research is being held on their ability to destroy bacteria and viruses.
http://www.nite.go.jp/data/000079898.jpg
[SIZE=3]Water with ultrafine bubbles (left) and pure water (right)[/SIZE]
[SIZE=3]Ultrafine bubbles are visible with the aid of laser light scattering[/SIZE]
[SIZE=5]Applications[/SIZE]
[SIZE=5]Water and wastewater treatment:[/SIZE]
[ul]
[li]Biological process enhancement[/li][li]Reduction of waste sludge[/li][li]Odour removal[/li][li]Floatation of pollutants[/li][/ul]
[SIZE=5]Surface water cleaning:[/SIZE]
Enhanced aeration/oxygenation of water
Algae removal, Nitrogen and Phosphorus reduction
Floatation of pollutants, suspended and settled solids
[SIZE=5]Agriculture:[/SIZE]
[ul]
[li] Crop growth promotion[/li][/ul]
[SIZE=5]Aquaculture:[/SIZE]
[ul]
[li]Oxygen supply in fish farms.[/li]
[li]Fish/Seafood growth promotion[/li][li]Floatation of suspended solids[/li][/ul]
[SIZE=5]Semi-conductor industry:[/SIZE]
[ul]
[li]Separation of solar cell wafer[/li][/ul]
https://www.youtube.com/watch?v=r4rJKypLijA
https://www.standards.govt.nz/touchstone/health/2014/nov/a-bubbling-potential-for-nz/
https://www3.nhk.or.jp/nhkworld/en/tv/scienceview/201702140600/