Published in Resource by Libby Peake | 19 November 2014
Charles Moore, the man who first discovered the now infamous Great Pacific Garbage Patch in the North Pacific Subtropical Gyre, has famously claimed that cleaning it up would be impossible: “Trying to clean up the Pacific gyre would bankrupt any country and kill wildlife in the nets as it went”, he’s proclaimed.
And there’s no denying that the plastic-ridden expanse of the North Pacific, the largest of five oceanic gyres where plastics collect in slowly rotating currents, is a challenging environmental nightmare, one that can’t be fixed with a fleet of carbon-emitting and net-dragging boats.
The Algalita Marine Research and Education Foundation, where Moore works, describes the garbage patch as ‘a “plastic soup”, where the plastic is distributed throughout the water column’, taking up an area of the ocean roughly two times the size of Texas. With most of the plastic broken into small pieces through exposure to the sun’s ultraviolet radiation, the foundation presents this disheartening analogy for those ambitious enough to think it can be cleared: ‘Think of how difficult it would be to gather confetti from along a stretch of beach. Now imagine the area you are trying to clean is not only miles long, but also miles deep.’
The photodegraded plastic, which outnumbers plankton by a ratio of six to one, is often mistaken as food by marine life and, even when it doesn’t directly kill those that ingest it (and it reportedly kills at least a million sea birds and hundreds of thousands of marine mammals each year), it can enter the food chain, bringing with it a whole host of undesirable chemicals – hormone disrupters like bisphenol A and potential carcinogens like styrene monomers – that the plastic releases as it degrades, as well as hydrophobic fertilizers and herbicides that it absorbs in the marine environment.
It’s a bit of an overwhelming problem, and, with environmental dilemmas like this, “the common response is ‘Well, that’s a long way off. That’s for our children to worry about’”, according to Boyan Slat. Speaking in the video of his TEDx talk in his home city of Delft, Netherlands, Slat follows that assertion with a cheeky grin and the statement: “Hello. Here I am.”
At the time of giving his talk, Slat was just 17 years old and was presenting his concept for a passive oceanic cleanup system, which grew out of a high school science project. Slat explains: “I realised, back in high school, that there might be an alternative [to a cleanup process based on vessels with nets that would be fishing for plastic]. I wondered: why move through the oceans if the oceans can move through you?
Instead of going after the plastics, you could simply wait for the plastic to come to you, without requiring any added energy. An array of floating barriers would first catch and then concentrate the debris, enabling a platform to efficiently extract the plastic afterwards. The ocean currents would pass underneath these barriers, taking… sealife with it, preventing by-catch. An elegant idea. But when I got asked to present this idea at the TEDx Delft conference, it wasn’t much more than that – an idea.”
After presenting his idea at TEDx, Slat started studying aerospace engineering, but, he says he couldn’t stop thinking about ocean plastics and so turned to professors and industry experts to help compile a list of 50 questions that needed to be answered to call his idea a feasible solution.
He subsequently suspended his studies to set up The Ocean Cleanup foundation, and used crowdfunding and the work of many volunteers and professionals in many fields – including ecology, engineering, fluid dynamics, plastic processing and maritime law – to conduct an extensive feasibility study into the idea. This summer, the foundation released a 530-page report claiming that the idea is indeed feasible.
“The basic concept and all the basic principles – so, the catching of the plastics, the concentration of the plastics – haven’t changed and have in fact now been validated, but what has changed now is some of the details”, Slat tells me, adding: “For example, how the mooring systems work, what the platform looks like – at first it looked like a fancy UFO crashed into the ocean; it now more closely resembles an oil rig [see image on p.51].
Basically, when I made these concept designs, I didn’t have any knowledge whatsoever, there was no one helping me three years ago. Now, fortunately, having worked with a team of 100 people, including 70 scientists and engineers – we’ve been able to develop this.”
It’s mainly the details that have changed, and, Slat says, they now have more accurate estimates for many aspects of the project. The study conservatively estimates that there are 140,000 tonnes of plastic floating in the North Pacific gyre – 119,000 tonnes of particles larger than two centimetres and 21,000 tonnes smaller than two centimetres (see boxout on microplastics on p.54).
Most of this plastic, according to the study, is concentrated close to the surface of the water, with mass decreasing exponentially with depth, leading to the conclusion that the floating barriers should be placed at a depth of two to three metres to collect the greatest mass of plastic pollution.
The design of these floating booms has also changed, as tests found that long booms with high tension wouldn’t be able to work with the movements of the waves, and in fact could ‘overtop’, likely losing some of the plastic collected. The Ocean Cleanup has attempted to address the problem with a design that sees boom and tension cable separated, with booms connected to the cable every 60 metres. The booms are comprised of floating buoyancy elements with weighted ‘skirts’ – thin, impermeable and flexible sheets that direct the plastics – hanging to a depth of two to three metres.
They will be positioned in a ‘V’ shape, and angled toward a central platform with the aim of concentrating the plastic; the models show that 80 per cent of the plastic that encounters the booms will be captured. It will then collect at the moored processing platforms that Slat says look like oil rigs (though some might think they’re remarkably like air traffic control towers anchored to the sea floor), from which it will have to be picked up by ship every 45 days.
Slat explains that this system is highly scalable and that the percentage of plastics that it can capture depends on the scale of deployment: “If you deploy a single system with a length of a hundred kilometres, you would collect 42 per cent of the plastic in the Great Pacific Garbage Patch, where about a third of all plastics from all oceans combined can be found.
But if you deploy something that’s, say, 200 kilometres, you would collect about two-thirds of the Great Pacific Garbage Patch. If you use a hundred-kilometre device and deploy it for 20 years, you would collect about 75 per cent, so it really depends on these variables. We can say that the majority of plastics in this area can be collected using this system.”
And it’s not just the collection of plastic that the foundation is looking into – it’s also considering what to do with the harvested material. The feasibility study involved collecting half a tonne of plastic from a remote Hawaiian beach, considered to be a ‘representative’ sample of gyre debris. This waste was tested by pyrolysis companies, which found that ‘the quality of the pyrolysis oil obtained from the polyolefin fraction of marine debris is comparable to that obtained as regular input in their pyrolysis plants’.
The cover of the 530-page feasibility document itself was also made using ocean plastics treated with a heat press. Slat proudly displays the finished product saying: “You can still see that it’s made out of ocean plastic because you have these weird colours that look kind of cool.”
Since completing the study, Slat tells me, they have also done some experiments into recycling the plastic through injection moulding, and that “the quality by far exceeded our expectations”. “The injection moulding was 50 per cent polypropylene, 50 per cent polyethylene. The only preprocessing was washing to remove any organic contaminants. Of course, it will certainly be downcycling in a way because you can’t use it for food packaging, and we’re still doing some chemical analysis of it to see if there’s any contamination that we should worry about.” That being said, he still anticipates any number of things could be made out of the material – “computer screens or chairs or anything you can imagine”.
Putting the plastic to good use will also offset some of the costs of the project, and perhaps even make it profitable: “Because of the premium of it being ocean plastic, I think there’s definitely a market for it, and I’m confident that it can cover at least part of the costs of the execution”, Slat says. The study estimates that it would cost €317 million (£247.5 million) to remove 42 per cent of waste from the North Pacific Gyre over 10 years; to break even, the project would need to receive €4.53 (£3.54) per kilogramme of collected plastic.
But all this is still a few years off. Following the triumphant launch of the feasibility study, The Ocean Cleanup created another crowdfunding campaign, this time seeking US$2 million (£1.2 million) to proceed to the next phase of testing. When I spoke to Slat several days before the deadline, the pledges were still US$70,000 (£42,900) short, and the situation was “rather tense”, though he assured me the research would continue with or without the funding, albeit at a much slower pace in the latter case. As it happened, the campaign raised more than US$2.15 million (£1.32 million), making the next steps much easier.
“Now, we’ll start the pilot stage and through a series of upscale tests, we’ll work towards this large-scale operation of a pilot in about three to four years’ time”, Slat explains. “We’ve shown that the concept is likely feasible, but now we have to also make it executable. There are some factors that primarily influence the costs as well as the efficiency.
So, there is a large uncertainty of the amount of plastic in the area, so that’s something that we will be working on. And then there’s the variability of the current, which will likely influence the collection efficiency. In the next year, we will mostly be doing controlled environment tests, then we’ll go to coastal waters and then in two years’ time, we’ll be ready to go to the centres of the gyres to do tests there and deploy a large-scale device. That should be the final stepping stone before actually doing it on the full scale.”
This article was taken from Issue 78
In the coming years, The Ocean Cleanup will also be continuing to emphasise the importance of preventing plastics from reaching the oceans in the first place: “Just because we have a way to clean up what’s already out there, it shouldn’t be an excuse to continue pollution, but now should be the time that we really do our best to make sure that the tap is closed, as well”, Slat says, and indicates that the project could also look at ways to intercept plastic before it reaches the ocean.
So there is still a lot of work to be done, but there are certainly reasons to be optimistic. And even the famous Garbage Patch discoverer and cleanup naysayer isn’t overly pessimistic about the project’s prospects: Slat tells me he had “a wonderful four or five hour discussion” with Charles Moore about his concept, and the captain “wasn’t too negative about it” (though he was “definitely sceptical”).
“Human history is basically a list of things that couldn’t be done and then were done”, the tireless and optimistic young man proclaimed when launching the feasibility study. Here’s hoping we can soon add cleaning up the oceans to that list…