5How the oceans can clean themselves

The last couple of days several (spontaneous) articles have been published, claiming The Ocean Cleanup Array is a ‘feasible method’ of extracting plastic from the gyres.

This is an incorrect statement; we are currently only at about 1/4th of completing our feasibility study. Only after finishing that study, we believe such statements should be made.

Although the preliminary results look promising, and our team of about 50 engineers, modellers, external experts and students is making good progress, we had and have no intention of presenting a concept as a feasible solution while still being in investigative phase.

Please stay tuned for this study, which will be published online in several months’ time. We kindly request the press to refrain from any further publication, until all assumptions of this concept have been confirmed.

Thank you | Boyan Slat

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Millions of tons of plastic debris are polluting world’s oceans eternally.

Plastic reaches the oceans mostly from land trough rivers and waterways, and then accumulates in 5 areas of high concentration, called gyres.

Not only does it directly kill hundred-thousands or even millions of aquatic animals annually, its fouling may spread harmful algae and other invasive species, and furthermore serves as a transport medium for pollutants (including PCB and DDT), accumulating in the food chain.

Plastic pollution costs governments, companies and individuals millions of dollars in damages per year, due to loss in tourism, vessel damages and (inefficient) beach clean-ups.

Plastic remediation will be extremely effective, but it must be remembered that a clean-up operation will always need to be paired with prevention (on land) in order to succeed.

We’ll need a combination of both worlds, and we’ll need them soon.

The concept

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How much plastic can this prototype get up ?

Approximately 1/3 of global ocean surface plastic pollution. This we estimate to be 7,250,000,000 kg.
We calculated this by combining data from scientific publications and our own measurements outside gyres with a computer density prediction model.

With our estimation, we tried to be as complete as possible by including both microplastics and large debris, like ghost nets.

Because this calculation has a very large margin for error, we are now repeating the same extrapolation with 2 other plastic accumilation models, and will include many more datapoints.

How does it work ?

The essence of The Ocean Cleanup Array is, instead of fighting it, to use the ocean to your advantage.
The gyres are 5 areas in world’s oceans where rotating currents create an accumulating mass of plastic, dubbed ‘Garbage Patches’.

Moving through the oceans to collect plastic would be costly, clumsy and polluting, so why not let the rotating currents transport the debris to you?

With The Ocean Cleanup Array, an anchored network of floating booms and processing platforms will span the radius of such a gyre.

These booms act as giant ‘funnels’, where an angle of the booms create a component of the surface current force in the direction of the platforms.

The debris then enters the platforms, where it will be filtered out of the water, and eventually stored in containers until collected for recycling on land.

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How is plastic separated from marine life ?

One of the most significant advantages of using booms instead of nets is that marine life cannot be caught in them. Furthermore, because the transport of plastic along the booms is driven by the currents, it’s slow enough for organisms to escape.

Because plastic accumulates along the booms and zooplankton does not, the ratio between zooplankton and plastic is (in theory) negligible.

This is one of the aspects that will be tested in the pilot project.

Our (tested) alternative is separating the small plankton and plastic using centrifugal forces, based on a density difference.

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How long will it take to clean up a gyre ?

About 5 years. OSCURS drifter tracking models show the natural rotational period of the gyres’ currents is approximately 5 years.

However, since surface currents are largely driven by wind, there is a degree of variability.

The idea is to span The Ocean Cleanup Array as a radius of these rotating systems, and thereby intercepting the moving debris.

Since it concerns a certain angular velocity, the time it will take is independent of the covered area (or radius).

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Is it a perfect solution ?

No. We will be able to retrieve billions of kilograms of plastic from the oceans, but that still won’t be 100% of what’s in the world’s oceans.

We’ll need a combination of extraction from the oceans and prevention on land in order to succeed.

One of the problems with preventive work is that there isn’t any imagery of these ‘garbage patches’, because the debris is dispersed over millions of square kilometers. By placing our arrays however, it will accumulate along the booms, making it suddenly possible to actually visualize the oceanic garbage patches.

We need to stress the importance of recycling, and reducing our consumption of plastic packaging.

Furthermore, by developing systems that will intercept plastic before it reaches the sea, we hope to further reduce the impact of plastic on the oceans.

Does it interfere with shipping traffic ?

This is of course essential for the concept to be implemented. Key is that the Ocean Cleanup array will not obstruct shipping routes.

The array will be placed parallel to those shipping routes, preventing any issues.

Besides, most gyres are located in scarcely sailed areas.

Accoring to our maritime law expert and IMO advisor, the Ocean Cleanup Array would be classified as an ‘artificial island’ under UNCLOS (international waters convention), but so-called ‘Areas to be avoided’ should be set, to prevent any conflicts with vessels.

Furthermore, The Ocean Cleanup Array will have to be charted.

But because it is not realistic to block the entire radius of a gyre from ship crossings (a), several of these ‘gaps’ (b) will be introduced to the array.

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Source | Boyan Slat

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