How do nanobubbles keep algae at bay?
Green algae, such as the type found in the Lincoln Memorial Reflecting Pool, thrive in still or slow-flowing water with abundant sunlight.
In water treatment, nanobubbles are used primarily to oxygenate water. This promotes the growth of aerobic bacteria which consume organic nutrients, outcompeting the algae and promoting a healthy aquatic environment.
Nanobubbles can also be used to deliver ozone gas, which is a highly reactive, toxic gas composed of three oxygen atoms. Ozone plays an essential role in the stratosphere in shielding Earth from ultraviolet rays, but it plays a very different role in water treatment.
Ozone reacts with organic materials in water and will therefore break down and kill the algae and nutrients. However, ozone nanobubbles also attack and kill the favourable aerobic bacteria.
The strong action of ozone nanobubble treatment is highly suitable for the treatment of heavily contaminated water – for example, if it contains animal waste.
In the case of the Lincoln Memorial, ozone nanobubbles can quickly resolve an algal bloom, but that comes at the cost of removing aerobic bacteria which could naturally keep the algae in check.
This would then make the pool susceptible to later algal blooms if measures are not taken to prevent a reoccurrence, such as preventing the build-up of nutrients the algae depend on.
The Reflecting Pool at the heart of Washington, DC is now set to be drained again to remedy the rapidly peeling new coating and the algae bloom. It remains to be seen what colour the water will end up being in time for July 4, and whether authorities will switch to oxygen nanobubbles to promote a healthier ecosystem in the water.
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