The new technology is being applied to a Dutch river to help stop plastic pollution reaching sea.
Five years ago, Claar-els van Delft began to suspect that plastic waste on the beach at Katwijk in the Netherlands did not come from visitors, or the sea, but from the mouth of the nearby Oude Rijn river. With further research, he proved his hunch to be correct.
Fast forward to July 2022, and Katwijk is the site for the world’s first river “bubble barrier” – an experimental concept where a 120-metre stream of rising bubbles, plus the water current, pushes plastic waste to one side in order to be collected.
“We place a perforated tube on the bottom of the waterway, at an angle, and then pump through compressed air: the rising air bubbles create an upward current that will lift plastic from the water column to the surface, and then at the surface – together with the flow of the river – it is all pushed to one side,” explains Philip Ehrhorn, the chief technology officer at the Dutch startup The Great Bubble Barrier. “Here, we get the flow from the pumping station, or the wind can also push trash into the catchment system.”
After a successful pilot scheme in a canal in Amsterdam (pictured above), 12 municipalities and the Holland Rijnland and Zuid-Holland regions have agreed to invest €470,000 to build their river bubble barrier across the Oude Rijn river.
Bas Knapp, an executive board member at the Rijnland water board, is investing €42,000 a year to run it. “We did a test which showed that in the pumping station, only one in 233 pieces of plastic larger than 1mm is removed from the water [by its filter],” he says. “But with the bubble barrier, we expect between 86 percent and 90 percent of the plastic pollution to be removed. A trial was incredibly promising. This is one of our largest river mouths, and a really good place to put a promising pilot to work to try to reduce plastic going to the sea.”
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