Millions of tons of plastic are circulating in rotating gyres throughout the world’s oceans. It is estimated that the dry weight of the plastic is six times more than the total weight of zooplankton in these gyres. One third of the ocean’s plastic accumulates within the so called “great pacific garbage patch“, which is a gyre of marine debris with an estimated size ranging from 700,000 square kilometers to more than 15,000,000 square kilometers. Ocean pollution has enormous ecological as well as economic effects. Animals are eating up the plastics, thus, the plastics end up in the food chain. It is also estimated that global ocean pollution by plastics costs $13 billion each year (the cost of removing plastic debris from beaches as well as repairing small boat and large vessel damage).
A way to filter plastics from the ocean using natural currents has been developed by 19-year-old Boyan Slat. His approach uses solid floating barriers, placed at locations within the ocean’s gyres, which collect all plastic particles in the ocean’s top-layers without trapping or otherwise harming marine animals. In contrast to nets, solid barriers allow fish to easily swim underneath. Slat’s approach seems to be highly scalable allowing high capture efficiency.
Slat envisions a 100-km-long solid floating barrier, which would be the largest structure ever installed on the open seas. Two 50-km-long barrier arms would have to be arranged in a funnel with a 120 degree opening for the further transport of the plastics into the funnel towards a platform where they are collected, compressed and picked up by a ship eight times per year. The barriers would have to be anchored to the approximately four-km-deep ocean bed. In a recent TED talk, Slat estimated that 7.25 tons of plastic can be filtered out the ocean within the next five years using his idea.
According to Slat, more money could be made with the recycled plastic than the costs of realizing his idea. A feasibility study has been provided by Slat and his team. However, critics point out that Slat’s feasibility study is not realistic. First of all, the proposed structure is believed not to be stable enough to resist high waves during storms. So far the deepest anchor constructions in the deep sea reach down to 2.5 km. Another problem could be the capturing of marine animals who live in the ocean’s top-layers. These organisms could settle on the accumulated plastics and travel down the funnel. It is also believed that only large plastic particles can be captured with such a structure since microparticles, which are smaller than five millimeters, can be pushed down 150 m below sea level during storms. Further test studies would have to be conducted to gain realistic estimations of the benefits and disadvantages of Slat’s proposed idea. Slat’s answer to the critics and updates on his approach and feasibility study can be found on the official website of The Ocean Cleanup.