Lincoln: Lincoln Memorial Reflecting Pool becomes real-life test case for nanobubbles, tiny air bubbles that can purify water, fight algae and potentially help restore polluted lakes and oceans
zThe Lincoln Memorial Reflecting Pool in Washington, D.C. is more than just a landmark. It’s now a real-world testing ground for nanobubbles, tiny air bubbles that can purify water, control algae and ultimately may help restore oxygen-starved lakes and oceans.Authorities turned to the technology ahead of celebrations marking the 250th anniversary of the United States’ Declaration of Independence after a bright green algae bloom appeared in the famous Reflecting Pool, despite a major cleanup just months earlier.To solve the problem, a $1.7 million (£1.27 million) ozone nanobubble system was installed. The device injects tiny ozone bubbles into the water to help break down algae and organic matter while keeping the pool clear.While the system has proven effective in controlled environments, scientists say its greatest promise may extend far beyond ornamental pools and into some of the world’s most polluted lakes, reservoirs and coastal waters.
What are nanobubbles?
Nanobubbles are extremely small air bubbles, usually filled with oxygen, air or ozone. Unlike regular bubbles, which quickly rise to the surface and burst, nanobubbles can remain suspended in water for longer periods of time.When ozone is used, the bubbles act as a powerful oxidizing treatment, attacking algae and organic matter that cloud the water.This makes them ideal for the Lincoln Memorial Reflecting Pool, which is shallow, has a hard artificial base and relies on clear water to maintain its appearance.The pool is also easier to manage than a natural lake because the water can be continuously circulated and treatment can be carefully controlled.
Bigger challenges beneath the surface
Cleaning your ornamental pool is only part of the story.Scientists are now investigating whether nanobubbles could solve a more difficult environmental problem, restoring oxygen to lakes and oceans where aquatic life is disappearing from the bottom up.Many lakes and coastal waters suffer from eutrophication, which is caused by excess nutrients such as phosphorus and nitrogen entering the water through sewage, fertilizers and agricultural runoff.The extra nutrients promote rapid algae growth. While these blooms are easy to spot on the surface, they are just one sign of a larger problem.When algae die, they sink to the bottom and bacteria begin to break them down. This process consumes large amounts of oxygen, rendering deeper waters anoxic, which is a lack of oxygen, or even anoxic, which is an almost complete absence of oxygen.Once oxygen levels collapse, the lake or ocean floor begins to release more phosphorus that was deposited in the sediment. These nutrients then feed more algal blooms, creating a cycle that becomes increasingly difficult to break.Fish die, biodiversity declines, and large areas of water become depleted of oxygen and become so-called “dead zones.”
Deliver oxygen to where it’s needed most
For years, engineers have been looking for ways to increase oxygen levels in damaged bodies of water.The challenge isn’t just adding oxygen to the water. It’s delivering oxygen into the thin layer where the water meets the bottom sediment. This is where phosphorus release, methane production, and many chemical processes that damage ecosystems occur.Researchers are exploring two different ways of using nanobubbles.The first involves bulk nanobubbles. The machine pumps oxygen-filled or ozone-filled nanobubbles into the water. This method already works in fish farms, wastewater treatment plants, swimming pools, tanks and smaller bodies of water where circulation can be maintained.Using the same method in a large lake or ocean is much more complicated.The equipment must operate continuously and relies on pumps, pipes, cables and electricity to distribute oxygen. Covering large areas requires extensive infrastructure while still not guaranteeing that enough oxygen will reach the bottom sediments.
Different ways to use sinking particles
Scientists are also working on another technique that could reduce these challenges.Oxygen nanobubbles can attach to the surfaces and tiny pores of solid materials, such as modified clays or other naturally porous particles, rather than dispersing the bubbles throughout the water.These oxygen-carrying particles sink under their own weight and deliver oxygen directly to the deposit layer where it is needed most.The approach could reduce energy use while avoiding some of the ecological damage caused by large-scale artificial lake and ocean mixing.If enough oxygen reaches the sediment surface, it could reduce the release of phosphorus, suppress methane production, and create healthier conditions for aquatic life living near the bottom.Unlike traditional oxygenation projects, the goal is not to oxygenate an entire lake or ocean, but rather to target the area where many environmental problems begin.Scientists warn that the technology is not a complete solution. Oxygenation alone will not stop eutrophication if untreated sewage or fertilizer runoff continues to enter rivers, lakes and coastal waters.Instead, recovery depends on removing excess algae and nutrients from the water, locking nutrients into the bottom sediment, and maintaining oxygen at the sediment surface to reduce future nutrient release.
Lessons learned Baltic Sea
The Baltic Sea is one of the world’s most famous anoxic marine environments, illustrating the importance of targeted oxygen supply.The ocean is naturally fragile because it exchanges relatively little water with the ocean through narrow connecting waterways. It also has unique surface and deep water layers that rarely mix, allowing oxygen levels in the deeper water to drop while nutrients continue to leak from the seafloor.One of the most ambitious attempts to address this problem began in 2009 with the Deepwater Oxygenation Project.The scheme relies on about 100 offshore wind pumps to move oxygen-rich water from a depth of about 50 meters to oxygen-depleted water about 125 meters below the surface.While increasing oxygen levels, the project also highlights the scale of the challenge. Such systems require large infrastructure, ongoing maintenance and large amounts of energy, while also raising questions about long-term costs and possible impacts on natural water cycles and marine ecosystems.The researchers believe that oxygen-carrying nanobubble clay materials could provide an alternative to allowing oxygen to naturally sink to the seafloor, potentially reducing energy consumption and ecological disruption.
