Cleaning up the Great Pacific Garbage Patch

What do six decades of a throwaway culture look like? Welcome to the Great Pacific Garbage Patch – a trash vortex between California and Hawaii thought to contain over 140,000 tonnes of floating plastic (the contents of around 12,000 rubbish trucks) washed into the sea from dumps, sewers and rivers.

Of the five major concentrations of ‘garbage-soup’ in the world’s oceans, the Pacific Garbage Patch is the largest (estimates range from twice the size of Britain to as big as Texas). It is also the focus of a controversial engineering project called The Ocean Cleanup (TOC), whose successful crowdfunding may point to a new way of tackling global environmental problems.

TOC hopes to remove half the Pacific Patch plastic in 10 years using a 100km array of floating barriers moored to the seabed at an estimated cost of £265m (£3.80 per kilogram of collected debris).

Resembling temporary booms for containing oil spills, TOC’s barriers will concentrate the rubbish on to platforms using the same large-scale offshore circular sea currents (gyres) responsible for pulling plastic rubbish into ocean patches in the first place. In this case, the North Pacific gyre, which rotates clockwise around an area of 20,000,000km², will be doing the work. Boats will pick up the plastic for recycling.

Most ocean-cleaning initiatives target ‘turning off the taps’, i.e. stopping the flow of plastic litter – over eight million tonnes a year – from the land. Packaging is the main culprit. Without such measures, plastic in the sea will outweigh fish by 2050, according to the Ellen MacArthur Foundation’s January 2016 report, ‘The New Plastics Economy: Rethinking the Future of Plastics’. Even by 2025, projected increases in plastic production indicate the plastic-to-fish ratio will reach one-to-three, as plastic stocks in the sea grow from 150 million tonnes today to 250 million. While the USA, Europe and Asia jointly manufacture 85 per cent of plastic, the report says Asia is responsible for 80 per cent of leakage into the sea.

“Bailing out the bath while the taps are still running,” as the TOC project plans to do, is viewed by many experts as a distraction. “It’s a different philosophy,” says Richard Thompson, professor of marine biology and head of the International Marine Litter Research Unit at Plymouth University. “Only a small proportion of the plastic that has entered the ocean is still floating on the surface. The rest is on beaches, on the sea floor, or in animals. The best investment is in preventing litter entering the environment.”

Boyan Slat, TOC’s charismatic young founder, came up with his array design while studying aerospace engineering at Delft University of Technology. No one would take the technology forward until Slat gave a TEDx Delft talk in 2012, ‘How the Oceans can Clean Themselves’. Since then, he has raised over $2m in crowdfunding from more than 38,000 funders in 160 countries. Four years on, TOC has installed its first prototype, a 100m barrier, in the North Sea, 23km off the Dutch coast. It will remain there for a year, with sensors tracking motion and the loads it is subjected to. A pilot for the Great Pacific Garbage Patch is planned for late 2017, prior to starting the big Pacific clean-up in 2020.

Slat’s initiative is idealistic. The funding is novel. Yet it is a professional engineering project. Between April 2013 and May 2014, TOC investigated the technical and financial viability of the array concept with costs covered by crowdfunding. The feasibility study covered everything from fluid dynamics to preliminary testing in a 45x36m tank with wind, wave and current generators at Marin (the Maritime Research Institute Netherlands).

The North Sea prototype is testing whether the design can stand up to worst-case conditions in the Great Pacific Garbage Patch, where it will be moored far offshore in deep water, and expected to collect plastic for years with minimum maintenance. That is no walk in the park. Designing offshore structures is almost as tough as spacecraft engineering, says Cranfield University’s Dr Maurizio Collu, expert in the conceptual and preliminary design and coupled dynamics of offshore support structures for renewable energy devices.

Collu is one of a number of specialists TOC approached in April 2014 to review the feasibility report. “Sometimes a novel solution is presented as a silver bullet, but these guys took a very down-to-earth approach,” he says. “TOC brought in commercial offshore engineering professionals, and they looked at a range of aspects, including ocean engineering, oceanography and environmental impact. Everything is based on theoretical and numerical methodologies, but they have pushed those analyses to the state-of-the-art. At the same time, they do not claim to have solved all the problems or have a perfect solution. They have said clearly they need to do experiments to analyse weaknesses. It’s admirable.”

At the launch of the prototype late in June 2016, Slat noted that a successful North Sea test would not necessarily mean the prototype would survive. “I estimate there is a 30 per cent chance the system will break, but either way it will be a good test,” he said.

Two months later, the two outermost air chambers of the prototype had started to bend out of shape and underwater footage showed that shackles connecting the barrier to the permanent mooring system were failing.

Since then, the engineering team has been busy looking into different connections to the mooring system as well as to the barrier – so busy, indeed, that they would not discuss details. “We are evaluating what changes we may make to the barrier design for long-term durability. We now expect a redesigned version of the prototype will be back in the water early next year,” a spokesman says.

The priority is to make sure that the pilot system works properly, he adds. “This way we ensure we are testing specifically those aspects on the prototype that we need to understand and master for a successful pilot and ocean deployment.”

Early in 2016, a study of ocean plastic movements by Dr Erik van Sebille and Peter Sherman from Imperial College London cast doubt on whether placing plastic collectors in the North Pacific gyre made sense, suggesting that coasts, particularly around China and the Indonesian islands, would be better sites.

Their computer simulations of a 10-year project between 2015 and 2025 showed that coastal collectors would remove 31 per cent of microplastics (particles under 5mm), whereas collectors in the Pacific Garbage patch gyre would remove only 17 per cent. The report was published in Environmental Research Letters.

Could TOC’s calculations be wrong? TOC says: “From its start, TOC has decided to focus its work on the gyres. First, because we had (and still have) a plan, and the idea of van Sebille and Sherman would require a different system and new engineering again. For us this would be an add-on, or a spin-off, but not a simple replication of the work we have been doing, and investing our funders’ money in.

“The van Sebille and Sherman proposal would not solve the entire problem because the gyres account for the largest concentration of plastic in the world and are the only places ... where plastic actually accumulates.

“Preliminary results from our expeditions show there are several tens of millions of pieces of plastic per km² in the garbage patches, while Law et al showed in 2014 that concentration outside the gyres is zero. If this accumulated plastic is not removed, it will slowly degrade into much more dangerous microplastics.

“The time to act is now.”

Slat’s ability to raise money and support is remarkable. Collu says it suggests that the general public is more interested in engineering research than we may imagine – certainly in the more emotive types of research. Crowdfunding, he speculates, may well be the only mechanism for solving some global, interdisciplinary problems. “Who makes money from cleaning the ocean? Economically, it doesn’t make sense to most investors or companies. It’s not a direct monetary return, it is an environmental return,” he says.

Cleaning up the seas is a monumental task. “We’ve had 60 years in training for the throwaway society, so it’s not going to happen overnight,” says Thompson. We need a range of approaches from novel clean-up schemes to re-thinking the entire plastics economy. As individuals, directing some of our passion for the oceans back to the land (and our rubbish bins) would be a start.