Rid the rivers of rubbish

The Great Pacific Garbage Patch (GPGP) is an area of floating waste plastic in the northern Pacific Ocean three times the size of France.

Containing 1.8  trillion pieces of plastic and weighing in at 80,000 tonnes, the GPGP is the visible symbol of the world’s waste plastic problem: 1.15 to 2.41 million tonnes of plastic enter the ocean each year, contributing to a grand estimated total of more than 150 million tonnes, or 5 trillion pieces of plastic floating in our oceans. Much of this consists of microplastics which enter the bodies of marine wildlife causing the deaths of an estimated 100 million marine animals a year.

The good news is that something is finally being done about it. A Dutch company, Ocean Cleanup, has begun clearing the GPGP using vast floating skirts that trap surface plastic, and is developing a scaled-up system after a year of trials. The bad news – it is not tackling the source of the problem.

That source is rivers – more than two-thirds of plastic in the oceans come from waterways, an estimated 80 per cent of which originates from just 1,000 rivers.

Fortunately several projects are starting to tackle this source, effectively looking to turn off the tap of waste plastic.

The Interceptor

Ocean Cleanup itself has developed one possible solution – the Interceptor (pictured above) – with the ambitious goal of halting 80 per cent of plastics entering the oceans from rivers by 2025. Two have already been deployed, in the Cengkareng drain in Jakarta, Indonesia, and the Klang river in Malaysia.

“The Interceptor is a barrier and conveyor-​belt system that concentrates and extracts plastic from rivers,” says Niels Broekhof of Ocean Cleanup. “The flow path is uninterrupted due to the catamaran design, which allows plastic to flow freely into the device and water to continue with the current.” Floating waste in the river is guided by two floating barriers positioned on either side so that waste is diverted towards the Interceptor while allowing boats and wildlife to pass through.

Once inside the opening of the Interceptor, a conveyor belt extracts it from the water, transferring it to a shuttle that drops the waste into one of six dumpsters, using sensor data to fill the containers equally. When the dumpsters are almost full the Interceptor automatically sends a message to local waste operators who remove the floating barge containing the dumpsters, pull it to the side of the river, empty it and return it to the system.

What happens to the waste after it is collected? What stops it ending up in landfill or, even worse, back in rivers? “The aim is to try to sort it and dispose of it as sustainably as possible,” says Broekhof. “This, of course, varies location by location, but when the standards are not there, we look to help with the initiation of better waste management when this is not available.”

The Interceptor has a 50m3 capacity and can collect 50,000kg of plastic a day working 24/7, and can achieve up to twice that amount in optimal conditions. The system is fully internet-connected, so performance and collection data can be monitored constantly from anywhere in the world. But with only two pilot systems currently operational in Indonesia and Malaysia, Broekhof says it’s still hard to get consistent figures. “Right now they do collect the vast majority,” he adds, “and as we learn more through their operations, we continue to make adaptions to increase efficiency.”

Ocean Cleanup’s ambitious plans for the Interceptor will require a fast roll-out. Two more Interceptors have already been built which are earmarked for near-term deployment in Vietnam and the Dominican Republic. There are also firm commitments from Thailand and from Los Angeles County in  the US. “Our long-term goals are to tackle the most polluting rivers by offering the Interceptor,” says Broekhof, “or by bringing knowledge through our research efforts, and using our network to raise awareness and help attract funding and financing.”

The Great Bubble Barrier

The Interceptor isn’t the only river plastic solution in the world, however, or even the only Dutch one. The Great Bubble Barrier is a system installed in an Amsterdam canal in November 2019 which cleans the waterway using nothing more than bubbles.

The idea originated from three friends who shared a passion for sailing and became concerned about the amount of plastic waste they saw in the water. Inspiration came one day when Anne Marieke Eveleens, Francis Zoet and Saskia Studer were sitting down over a drink. “One day they were drinking a beer in a bar,” says Sandy Reitsma of Great Bubble Barrier, “and discussing the problem of plastics in the ocean. One of them was looking at the bubbles in the beer and that was the start of the idea.”

The three women took their idea to the public and received funding from the Postcode Lotteries Green Challenge award and other prizes. At around the same time they were approached by a German naval architect and ocean engineer, Philip Ehrhorn, who had come up with a similar idea when watching bubbles in a water treatment plant bring waste plastics to the surface. The two projects merged and the Great Bubble Barrier was born.

The system is beautifully simple, consisting of a 60-metre-long perforated tube running across the bottom of the canal. The tube is filled with compressed air that produces a curtain of bubbles, which blocks plastics and forces them to the surface while allowing fish to pass through unharmed. “It’s placed at an angle which is perfectly calculated with the current of the river,” says Reitsma. “The bubbles force the waste to the surface and because of the diagonal placement it uses the natural flow of the river to guide the waste to the quay.”

This has the advantage of collecting waste from the whole depth of the river rather than just a few inches below the surface as with boom or skirt technologies. Initial tests in a river showed the device collected 82-86 per cent of test material. Once proven, the technology was installed in Amsterdam’s Westerdock canal in November, where it is powered by electricity from the grid. All waste collected from the canal is stored for analysis by collaborating organisation Plastic Soup Foundation, but the results are not yet available. Waternet, the organization that manages all water affairs within the city of Amsterdam, operates four garbage boats. Annually, they remove around 42,000 kg of plastic from their waterways.

Meanwhile the Great Bubble Barrier is looking to expand into other waterways in Europe and Asia and is already in talks with authorities in Indonesia. The system could also be effective at removing microplastics from waste water, with research already under way to test the process. “Ultimately our goal is to implement as many Bubble Barriers as we can in suitable rivers,” says Reitsma, “especially those rivers that are the most polluted, so now we are working really hard on implementing new Bubble Barriers.”

Mr Trash Wheel

The Great Bubble Barrier and Interceptor are exciting solutions, but they’re new kids on the block compared to the characterful Mr Trash Wheel, which has been removing waste from the mouth of the Jones Falls river in Baltimore since 2014. “Since that time we’ve collected over two-and-a-half million pounds [1,100 tonnes] of debris,” says John Kellet, Mr Trash Wheel’s inventor, “and it’s made a huge difference to the harbour.”

The googly-eyed contraption uses a floating boom to funnel waste onto a conveyor belt using the flow of the river, which also powers the machine itself via the large water wheel on its side. The inspiration for the idea came when Kellett, a former boat builder, was working as the director of the Baltimore Maritime Museum. “I was constantly going across the river and thinking about what we could do to stem the flow of waste into the harbour,” he says, “when the idea dawned on me that when the rain comes, that’s when you have the most trash coming, but it’s also when you have the most flow in the river so why don’t we use that flow to help us collect the trash?” A water wheel also fitted in nicely with Baltimore’s riverside industrial legacy where water wheels had been used for centuries in the paper, textile and food industries.

In 2008 Kellett built a prototype that worked well even though the figures he had been given about the amount of waste coming down the river were grossly underestimated. With the machine operating, people began to notice the harbour was much clearer so a group of businesses and stakeholders around the harbour, called the Waterfront Partnership of Baltimore, raised the money for a permanent version that was bigger, stronger and faster (and had eyes).

The permanent version was installed in 2014 and has since collected 1,230 tonnes of waste including 1,060,924 plastic bottles, 701,662 plastic bags, 1,161,782 polystyrene containers, a beer keg, a guitar and a python. The larger items make for interesting light-hearted stats but they also reflect some of the challenges the project has faced, mostly concerning robustness. “We’ve seen a couple of what they call thousand-year storms in the last couple of years, some crazy flooding,” says Kellett. “In that type of flow the debris is coming down at an incredible rate, so at that point it’s more about survivability and the machine has done extremely well. We’ve only had to replace the booms once in six years.”

To survive and be effective the booms need to strike a balance between robustness and buoyancy. So Kellett reinforced them with polyethylene strapping and attached a metal chain to the bottom of the barrier, just over half a metre below the surface. To add buoyancy he fixed moulded floats along the top of the boom. Another important factor was the angle of the boom. “Instead of blocking the flow, you want to guide the material to the side using the current,” he says, “so you want a pretty steep angle on it.”

Mr Trash Wheel has now been joined by Professor Trash Wheel and Captain Trash Wheel, with another member of the family due to come on line this year. The rapid expansion means plans to make Baltimore’s harbour swimmable and fishable this year could still be viable. But more than just a practical solution, the colourful Trash Wheel family has become something of an icon, raising awareness and encouraging education about the issues of waste plastic, which Kellett believes is crucial.

“To think we can technologically solve the problem by collecting plastic before it gets to the ocean is a delusion,” he says. “It’s just as important to draw attention to the problem and approach it from many different angles, like developing policies, educating the public and developing replacements for single-use plastics. It would be nice to envisage a world where we didn’t need things like Trash Wheels or Interceptors in the first place.”