Meet Mr Trash Wheel – and the other new devices that eat river plastic

Good News Notes:

The Great Bubble Barrier is just that – a wall of bubbles. It gurgles across the water in a diagonal screen, pushing plastic to one side while allowing fish and other wildlife to pass unharmed.

The technology, created by a Dutch firm and already being used in Amsterdam, is being trialled in the Douro River in Porto, Portugal, as part of the EU-supported Maelstrom (marine litter sustainable removal and management) project.

It is the latest in a series of new technologies designed to find sustainable ways to remove and treat river debris before it reaches the sea.

Plastic can be spread by natural disasters, such as a tsunami, which can push invasive species and debris halfway across the world. But rivers carry a much more regular supply of plastic to the oceans. Research in 2017 found that 10 river systems transport 90% of all the plastic that ends up in the world’s oceans (two in Africa – the Nile and Niger – with the other eight in Asia: the Ganges, Indus, Yellow, Yangtze, Haihe, Pearl, Mekong and Amur).

Molly Morse, a scientist at UC Santa Barbara’s Benioff Ocean Initiative and lead on its global Clean Currents Coalition, says: “In some cases, communities don’t have access to proper waste pickup services and must turn to what might seem to be the only alternative: dump the trash directly in the river to be carried away.

“In other cases, plastic litter on land is moved by rain or wind into a river, where […] the plastic may make its way to the ocean.”

An estimated 0.8m to 2.7m tonnes of plastic are carried by rivers to the ocean each year. That is the equivalent of 66,000 to 225,000 doubledecker buses.

Without barriers, river currents carry plastic directly to the sea, where it becomes far trickier to tackle: plastic often floats for vast distances, can host invasive species and becomes part of the wider plastisphere, such as the concentration of seaborne waste in the Great Pacific garbage patch.

That is why some scientists are calling for greater efforts to stop plastic going into rivers in the first place. A 2020 study found that a “significant reduction” of plastic in the ocean could be achieved only by stopping it reaching the sea, or through a combination of river barriers and other clean-up devices.

Cue inventors, who have developed an array of river barriers and collection devices to catch and remove riverine plastic – from simple nets and booms to conveyor belts and robots.

Mr Trash Wheel, known officially as the Inner Harbor Water Wheel, is a conveyor-belt system powered by currents and solar energy, launched in 2014 in the US city of Baltimore. Long booms with submerged skirts funnel waste into a central hub, where autonomous rakes scoop it on to a conveyor belt that deposits it on a barge, with more than 17 tonnes collected in a day.

Once full, the barge takes the rubbish to be incinerated in a power plant, though it is hoped that eventually the collected waste can be sorted and recycled. There is now a whole family of Trash Wheels in Baltimore, the latest addition being Gwynnda, the Good Wheel of the West.

Or there’s the Interceptor, a floating, solar-powered device developed by the non-profit organisation The Ocean Cleanup, billed as the “world’s first scalable solution” to rid the oceans of plastic. Similar but larger than the trash wheel, it has barriers that guide rubbish on to a conveyor belt, where a shuttle distributes it among five onboard waste bins.

Another design, the Azure barrier, developed by the UK-based startup Ichthion to operate in any river, can remove up to 80 tonnes of plastic a day using durable, tide-sensitive booms that direct plastic to extraction points along the bank. The plastic is processed into flakes for recycling.

Other more hi-tech inventions include the WasteShark, an electronically controlled “aquadrone” that preys on plastic – up to 350kg at a time. Using algorithms from the German Research Center for Artificial Intelligence, the WasteShark moves around and back to its docking station autonomously, where up to five of the catamaran-shaped vessels can deposit the collected plastic and recharge. The design, developed by a Dutch startup, RanMarine, is due to be showcased at CES 2022 in Las Vegas this month….”

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