Ever since the plastic pollution problem gained widespread attention at the beginning of this century, there have been many ideas for cleaning the plastic islands in the oceans up. But these all involved vessels and nets that would ‘fish’ for plastic. Not only would by-catch and emissions likely cancel out the good work, but also, due to the vastness of areas in which the plastics concentrate, such an operation would cost many billions of dollars, and thousands of years to complete.
In 2012, Boyan Slat —then 17 years old— proposed a passive concept that could overcome these challenges;
The Basic Principles
Passive collection
Why move through the oceans, if the oceans can move through you? Attaching an array of floating barriers and platforms to the sea bed enables us to concentrate the plastic before extracting it from the ocean —a collection process 100% driven by the natural winds and currents.
Capturing plastics, not sea life
Instead of nets, we make use of solid floating barriers, making entanglement of wildlife impossible. Virtually all of the current flows underneath these booms, taking away all (neutrally buoyant) organisms, and preventing by-catch, while the lighter-than-water plastic collects in front of the floating barrier.
Highly scalable
The scalable array of moorings and booms is designed for large-magnitude deployment, covering millions of square kilometers without moving a centimeter.
Thanks to its projected high capture and field efficiency, a single gyre can be covered in just 5-10 years (or longer, depending on the chosen deployment strategy).
After performing a year of research with a team of 100 volunteers and professionals, in June 2014 The Ocean Cleanup announced the successful outcome of its feasibility study. Here are some of its key points:
Novel boom design
After having determined the forces acting on floating barriers using computer software, engineers noted that a barrier anchored to the sea floor would pull tight under strain, stopping it from following the waves. To solve this problem, we came up with a new boom design in which the tension-carrying cable and the boom itself are separated, enabling the boom to move with the motion of the waves (like an inverted pendulum). Early tests suggests this significantly reduces the wave-induced forces.
Storm resistant
Using both computer simulations and scale model tests, we engineered a boom that can operate in over 95% of conditions. On top of that, a conservative safety factor of 2.5 was applied. And, if waves get even higher than predicted, the booms segments will decouple at one end, letting the waves move through the Array unimpeded, which will save the equipment from catastrophic failure.
Unprecedented efficiency
Using Computational Fluid Dynamics simulations, we calculated that approximately 80% of the plastic encountering the boom will be captured. We also showed that the plastic, including the submerged particles, will be transported along the angled booms, confirming that the Array can indeed concentrate plastic.
Tested concept
Small scale model tests indicated The Ocean Cleanup Boom to perform significantly better than conventional booms, while deploying a 40 m long boom near the Azores showed us that a boom can indeed capture and concentrate plastic pollution.
Environmentally sound
Although plankton will likely be taken away safely by the current, even if all of the plankton encountering the booms were to be destroyed, the time it would take for the biomass to regenerate would be less than 7 seconds a year. Because no nets are used, entanglement of fish or mammals is virtually impossible. Furthermore, the carbon footprint will be about equal to several hundred cars, a negligible amount compared with the alternatives.
Reusing ocean plastic
After collecting almost half a ton of plastic from the Hawaiian shoreline, The Ocean Cleanup measured how degraded the plastic was, which turned out to be surprisingly positive. With this knowledge we continued testing, and proved ocean plastic is suitable to be turned into oil. We have also been testing whether or not the plastic can be turned into new materials through mechanical recycling, with promising results.
Cost-effective
Thanks to small operational expenditures, high capture efficiency and the possibility of reusing the plastics, it will only cost €4,50 for every kg of plastic removed, about 33 times less expensive than conventional cleanup methods. This is excluding the value of the extracted plastic, which can potentially cover a major part of these costs. Considering the $ 13B the UNEP estimates is the annual damage of oceanic plastic pollution, it is likely more cost-effective to clean up then to leave it in the oceans.
After a series of scaled-up tests, The Ocean Cleanup now works towards a large-scale and fully operational pilot in 3 to 4 years’ time. The pilot is now funded!
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