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Biofiltration: How plants make swimming pools more “natural”


Water disinfection in swimming pools usually relies on chorine and chemicals. In recent years, however, cities and architects have become increasingly interested in the self-purification capabilities of aquatic environments to dispense with disinfectants and create “natural” swimming pools. While the first such capabilities were developed in countries with strong environmental sensitivities, such as Austria and particularly Germany, the first natural swimming pool opens this month right in the heart of London.

Situated in the King’s Cross urban regeneration zone, the 400 m2 artificial “Of Soil and Water: King’s Cross Pond” adheres to the principles of natural pools: no chlorine for water treatment and no heating system for swimmer comfort. The water is kept clean and clear by the filtrating action of carefully selected underwater plants. Even so, the balance of this ecosystem is fragile, which is why no more than 163 visitors are admitted per day.

Above and beyond the project’s environmental virtues—no chlorinated water released and no fossil fuels used to run the filtration pump—”Of Soil and Water” also has a ground-breaking artistic and educational purpose. The pond designers, a Dutch architectural firm (Ooze) and a Slovenian artist (Marjetica Potr), wanted to make it a laboratory and facility where people can understand how an ecosystem works, become aware of their relationship and interaction with nature, to make us all contributors to protecting nature.

The purification capability of aquatic environments is being increasingly leveraged to treat wastewater in both domestic and industrial systems. This is the case, for example, in Zone Libellule© (Biofreedom and the Fight against Emergent pollutants), an artificial wetland created by SUEZ environnement downstream of the St-Just-St Nazaire (France) purification plant, which hosts a wide variety of aquatic plants with cleansing power.

In that particular case, as in London, the environmental benefit is boosted by an educational benefit, as this wetland is now a place to visit and to learn, for the region’s students and residents.