Nanobubbles cleaned up the Lincoln Reflecting Pool: Here’s how to use them in dying seas and lakes
The Lincoln Memorial Reflecting Basin in Washington, D.C. has become more than just a landmark. It’s now a veritable proving ground for nanobubbles, microscopic gas bubbles that can clean water, control algae, and may ultimately help restore oxygen-starved lakes and seas.Ahead of celebrations for the 250th anniversary of the US Declaration of Independence, authorities turned to the technology after the famous reflecting pool developed bright green algae, despite undergoing a major clean-up just months ago.To address this issue, a US$1.7 million (£1.27 million) ozone nanobubble system was installed. The equipment injects microscopic ozone bubbles into the water, which helps break down algae and organic matter while keeping your pool clean.Although the system has proven effective in a controlled environment, scientists say its greatest promise could lie beyond ornamental ponds, in some of the world’s most polluted lakes, reservoirs and coastal waters.
What are nanobubbles?
Nanobubbles are very small gas bubbles, usually filled with oxygen, air or ozone. Unlike regular bubbles that quickly rise to the surface and burst, nanobubbles can remain suspended in water for a longer time.
When using ozone, the bubbles act as a powerful oxidant, attacking algae and organic matter blocking the water.That made it a perfect fit for the Lincoln Memorial Reflecting Pool, which is shallow, has a solid artificial base and relies on clear water to maintain its appearance.A swimming pool is also much easier to manage than a natural lake because the water can be circulated continuously and treatment can be carefully controlled.
A bigger challenge is beneath the surface
Cleaning an ornamental pond is only part of the story.Scientists are now investigating whether nanobubbles can tackle a much more difficult environmental problem, restoring oxygen to lakes and seas where aquatic life is disappearing from the bottom up.Many lakes and coastal waters suffer from eutrophication, a condition caused by excess amounts of nutrients such as phosphorus and nitrogen entering the water through sewage, fertilizers and agricultural runoff.Additional nutrients encourage rapid algae growth. While blooms are easy to spot on the surface, they are only one sign of a much larger problem.When algae dies, it sinks to the bottom where bacteria begin to break it down. This process consumes large amounts of oxygen, leaving deep waters anoxic, that is, oxygen-poor, or even anoxic, where there is almost no oxygen at all.Once oxygen levels collapse, the lake or seafloor begins to release more phosphorus trapped in the sediments.
These nutrients then fuel more algae blooms, creating a cycle that is increasingly difficult to break.Fish die, biodiversity declines, and large areas of water can become so depleted of oxygen that they turn into so-called “dead zones.”
Delivering oxygen where it’s needed most
For many years, engineers have searched for ways to increase oxygen levels in damaged bodies of water.The challenge is not just adding oxygen to the water. It delivers oxygen to the thin layer where water meets sediment at the bottom.
This is where phosphorus is released, methane is produced, and many chemical processes that damage ecosystems occur.Researchers are exploring two different ways to use nanobubbles.The first involves huge nanobubbles. The machines pump nanobubbles filled with oxygen or ozone throughout the water. This method works really well in fish farms, sewage treatment plants, swimming pools, tanks and small bodies of water where circulation can be maintained.Using the same approach in large lakes or seas is more complex.The equipment must operate continuously and rely on pumps, pipes, cables and electricity to distribute oxygen. Covering large areas would require extensive infrastructure, while offering no guarantee that sufficient oxygen will reach the bottom sediments.
A different approach using sinking particles
Scientists are also studying another technology that could reduce these challenges.Instead of dispersing bubbles throughout the water, oxygen nanobubbles can attach to the surfaces and small pores of solid materials such as modified clay or other naturally porous particles.These oxygen-laden molecules sink under their own weight and transport the oxygen directly to the sediment layer where it is needed most.This approach could reduce energy use while avoiding some of the environmental disruption caused by large-scale artificial mixing of lakes and seas.If enough oxygen reaches the sediment surface, it can reduce phosphorus release, prevent methane production, and create healthy conditions for aquatic life living near the bottom.Unlike traditional oxygen projects, the goal is not to oxygenate the entire lake or sea but to target the area where many environmental problems begin.Scientists warn that this technology is not the complete solution.
If untreated sewage or fertilizer runoff continues to enter rivers, lakes and coastal waters, oxygen alone cannot stop eutrophication.Instead, the restoration process relies on removing excess algae and nutrients from the water, trapping nutrients in the bottom sediment, and maintaining oxygen at the sediment surface to reduce future release of nutrients.
Lessons from Baltic Sea
The importance of targeted oxygen delivery is evident in the Baltic Sea, one of the world’s most notorious oxygen-depleted marine environments.The sea is naturally vulnerable because it exchanges relatively little water with the ocean through the narrow waterways connected to it. It also has distinct surface and deep water layers that rarely mix, allowing deep-water oxygen levels to fall while nutrients continue to seep from the seafloor.One of the most ambitious attempts to address the problem began in 2009 with the Deepwater Oxygen Project.
The plan relied on about 100 wind-powered marine pumps to transport oxygen-rich water from depths of about 50 meters to oxygen-starved water about 125 meters below the surface.While increasing levels of oxygen are being pumped out, the project has also highlighted the scale of the challenge. Such systems require significant infrastructure, ongoing maintenance, and significant energy, while also raising questions about long-term costs and potential impacts on natural water circulation and marine ecosystems.The researchers believe that materials made from clay nanobubbles that carry oxygen could provide an alternative by allowing oxygen to sink naturally to the seafloor, which could reduce energy use and environmental disturbances.
