The Concept

Ever since the plastic pollution problem gained widespread attention at the beginning of this century, there have been many ideas for cleaning it 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).

Feasibility Study Results

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.

The Next Steps

Through 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.

This series of tests will generate new data in a range of structural and physical disciplines. Furthermore, these scaled-up tests will serve as a platform for the engineering and oceanographic research groups, enabling them to immediately implement newly developed technology or testing equipment in a real-life environment.

The actual scale and function of each test will depend on the characteristics of the location, and the results of detailed engineering and oceanographic research, as well as the output of the previous tests. The scale will likely range from ~100 m at the scale model test (1:1000) to ~10 km in the large-scale operational test (1:10).

The majority of the oceanographic field research will be in the first 1 to 2 years, because many engineering topics require the oceanographic results as input parameters—environmental conditions, soil conditions, plastic flux, etc.

In addition to investigating pre-defined research topics (including forces, boom-particle interaction, moorings, survivability, etc.), and practicing operational procedures, these tests will serve to reveal any unforeseen interactions between the structure and the environment.