Patching the ocean mess
Over 5 trillion pieces of plastic waste have made their way into the world’s oceans. Captured by currents, they end up in one of five ocean gyres and concentrate on what oceanographers have named “garbage patches.”
The biggest of them, the Great Pacific Ocean, spans more than 617,000 square miles, more than twice the size of France.
The problem, however, starts a few miles back in the water cycle, since a big proportion of ocean plastic waste is river-borne.
In numbers, the majority of plastic pieces that make their way to the seas are “microplastics”, small, difficult to catch, and dangerous for ocean life, as they are mistaken for food.
The Challenges
The prey is hard to catch: pollution spans millions of square miles and is already sinking, as the plastic pieces degrade to microplastics.
The prey is hard to dispose of: recycle plants are on shore, at thousands of miles from the garbage patches.
The Ocean Cleanup research team has established that 1,000 rivers are responsible for around 80% of river-borne plastic waste in the ocean. Each of these rivers behaves differently and calls for a tailor-made approach.
Credit: The Ocean Cleanup
The Answers
In rivers
Different strategies have led to different results.
- Whole physical barriers in non-navigable rivers. These are designed to let water through and to retain macro plastics. The force of the water, especially in mountain rivers or during floods, can break the net.
- Partial physical barriers. They are conceived as floatable devices with three-meters-deep nets that serve a double purpose: to lead the water current and to direct the plastic waste to a mobile collector. The Ocean Cleanup’s model is the Interceptor: an automated debris filtration and extraction system that operates on solar power. A very similar device and its direct antecedent, Mr. Trash Wheel, has been operating in Baltimore for some time.
- Bubble barriers. More environmentally-friendly is a tube of air located at the bottom of a river that crosses its full width. It releases bubbles, that push plastic pieces to the surface, thus solving one of the issues the partial barrier cannot address: sinking trash. Once on the surface, the bubbles create a small current that leads the waste to an immobile trash collection unit.
The Answers
In oceans
For the ocean part, The Ocean Cleanup crew saw the need to create artificial coastlines -where there are none- to concentrate the plastic. The objective is to create a retention zone, and the strategy, to make a U-shaped barrier that guides the plastic there until a ship picks it up and takes it to shore for recycling.
There are still a few things to solve in that strategy: two ships carrying a net or barrier that covers 2500 m and advances at a very low speed is just not efficient enough. Furthermore, the need to go ashore to dispose of the plastic in recycling plants lengthens the process considerably.
If The Ocean Cleanup’s solution relies on Physics, The Sea Change (another non-profit organization) follows a different approach. They use proven plasma gasification technology as a mobile solution to eliminate 15 tons of plastic per day. The technology uses extreme heat from electrically conducting gas to break down the molecular structure of materials. Byproducts are clean fuel and a non-toxic, inert piece of glass.
Credit: The Ocean Cleanup
