Lincoln Memorial Reflecting Pool turns to nanobubbles to clear algal bloom
As Washington DC prepares for the U.S. 250th birthday, officials are using microscopic ozone-filled bubbles to fight a green algal bloom that fouled the Lincoln Memorial's freshly renovated Reflecting Pool.
Washington DC's iconic Lincoln Memorial Reflecting Pool has fallen victim to an algal bloom—a slimy green discoloration that emerged soon after renovations were completed ahead of July 4th celebrations marking the United States' 250th birthday. To address the problem, officials have deployed an unusual solution: ozone nanobubble technology to clean the water.
What nanobubbles are
Nanobubbles, also known as ultrafine bubbles, are gas-filled bubbles with diameters of roughly 100 nanometres—about one-thousandth the thickness of a human hair, according to reporting from The Conversation. When specialised equipment injects gases like air, ozone, or oxygen into water, nanobubbles form in staggering numbers: typically around 10 billion nanobubbles per teaspoon of water.
Despite their enormous numbers, solutions containing nanobubbles look and feel indistinguishable from ordinary water. A glass of nanobubble-treated water appears perfectly normal to the naked eye.
Why they work
Nanobubbles possess unusual stability that makes them valuable for water treatment. A fundamental principle of bubble physics is that pressure inside a bubble always exceeds that of its surroundings—and the smaller the bubble, the greater the internal pressure. A typical nanobubble can maintain internal pressure as high as 15 atmospheres, equivalent to the pressure experienced by a diver at 150 metres depth.
This high internal pressure dramatically increases how much gas can dissolve into the surrounding liquid. According to standard physics, nanobubbles should dissolve almost instantly—in less than a second. Yet research has shown they can persist for hours, days, or even weeks. The exact mechanism behind this surprising longevity remains a subject of active research.
Nanobubbles can be produced, stored and used before they disappear—making them practical for real-world applications.
Their tiny size also gives nanobubbles minimal buoyancy, allowing them to stay suspended in solution far longer than larger bubbles. Conventional bubbles rise quickly to the surface and burst within seconds, as anyone who has watched foam dissolve on a beach can observe. Nanobubbles, by contrast, maintain their position in the water column.
Because they are so small, nanobubbles possess a very large surface area relative to their volume. This combination of extended residence time, high internal pressure, and vast surface area makes them effective in applications ranging from mineral processing to wastewater treatment—and, now, algal bloom remediation at one of America's most visited monuments.