‘Incredibly promising’: the bubble barrier that extracts plastic from a Dutch river | Plastic

Five years ago, Claar-els van Delft began to suspect that the plastic waste on Katwijk beach in the Netherlands did not come from visitors, or from the sea, but from the mouth of a nearby river.

“We started collecting the waste and we noticed, near the river entrance, pieces that came from fresh water, all kinds of plastic,” he says. “Absorbent sleeves, brush bristles, but also packets of chips, packets of sodas, everything.”

Sure enough, when the volunteers sifted through an oil can full of water from the Oude Rijn River, they saw tiny particles of plastic among the duckweed. “We saw so much pollution that we were shocked,” says van Delft, co-founder of the local charity Coast Busters.

How the bubble barrier works

Fast forward to July 2022 and Katwijk is the site for the world’s first river “bubble barrier”, an experimental concept in which a 120-meter flow of rising bubbles, plus the current of water, pushes plastic waste. on the one hand to be collected.

“We place a perforated tube at the bottom of the watercourse, at an angle, and then pump through the compressed air: the rising air bubbles create an upward current that will lift the plastic from the water column to the surface. , and then to the surface – along with the flow of the river, everything is pushed to one side, “explains Philip Ehrhorn, Chief Technology Officer at the Dutch startup The Great Bubble Barrier.” Here, we get the flow from the pumping station, or the wind it can also push waste into the collection system. “

The company, run by a team of passionate sailors, surfers and water enthusiasts, won an international Postcode Lottery Green Challenge in 2018 and started its first permanent pilot in a canal in Amsterdam the following year. Such is the promise of this process that convinced the Rijnland Water Board, 12 municipalities and the Holland Rijnland and Zuid-Holland regions – along with Coast Busters and local fundraisers – to invest € 470,000 to build the river bubble barrier.

Plastic removed from waterways is sorted as part of the barrier bubble study.
Plastic removed from waterways is sorted as part of the barrier bubble study. Photography: Cynthia van Elk / The Great Bubble Barrier

Jacco Knape, deputy mayor of Katwijk municipality, said he saw the local plastic problem with his own eyes when he was asked to clean the beach. “Plastic pollution is a growing problem around the world, affecting communities and the environment, [and] Katwijk sadly is no exception, “he says.” We noticed plastic pollution from beach visitors, leaving wraps and other plastic behind, but we are also the last stop before all the plastic collected along the Oude Rijn flows into the sea. With this bubble barrier we can stop that plastic “.

Bas Knapp, executive council member of the Rijnland water council, believes the bubble reef will not prevent fish migration and is investing € 42,000 per year to manage it. “We carried out 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% and 90% of plastic pollution to be removed. A process was incredibly promising. This is one of our largest river mouths and it really is. a good place to put a promising pilot to work to try to reduce the plastic that goes into the sea ”.

Anne Marieke Eveleens, co-founder of The Great Bubble Barrier, is working to augment the technique, discussing a potential barrier in an estuary in Portugal and another project in Southeast Asia. “One of the requests we sometimes receive is for a large international port like Rotterdam: it is 20 meters deep there but it is [currently] out of reach, “he admits.” It’s also difficult if there are many ships and they are dredged several times a year. “

But many believe the technique still holds real promise for specific scenarios. Dr Frans Buschman, researcher in environmental hydrodynamics at the independent Deltares institute, tested the reef in Amsterdam, using around 1,000 tagged mandarins. “We released them in several places and counted how many were captured,” he says. “From the user system side, it has reached 90%; sometimes on the other hand we noticed that it was substantially lower, probably because there is a point where the intensity of the bubble is not that high and some mandarins were passing there. “

He adds that objects that floated fully could be blown over the bubble barrier by the wind, making it less effective, but he believes it is still a “promising technique.” [with] Great potential “.

The Great Bubble Barrier concept in operation in Amsterdam.
The Great Bubble Barrier concept in operation in Amsterdam. Photography: the great bubble barrier

Some researchers, however, point out that plastic from rivers doesn’t necessarily end up in the oceans, although they can still damage human ecosystems and livelihoods. Tim van Emmerik, assistant professor at the University of Wageningen’s group of hydrology and quantitative water management, says river systems are also different. “When you think of rivers globally, imagine how much they can vary, from the narrow canals of Amsterdam and Leiden to large deltas like the Mekong,” he points out. “Most technology solutions, such as Bubble Barrier, only cover one range, emphasizing that a portfolio of solutions will always be needed. Obviously, consuming and polluting less plastic will help, no matter where you go, and could in fact have the greatest impact ”.

In Katwijk, there are plans to build a visitor and education center near the bubble barrier to do just that, and hopes are high. Under the summer sun, a trickle of bubbles breaks the surface of the river, a bit like a hot tub. “We couldn’t wait,” says van Delft, seriously enough, “to come to the opening in a bathing suit!”

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