Published on September 18th, 2018 | by Michael Barnard0
Ocean Plastic Cleanup Project Is Better News Than You Might Think
September 18th, 2018 by Michael Barnard
Five years ago, Boyan Slat of the Netherlands had a vision. He saw the oceans cleaned of the plastic that was fouling them. He saw the inklings of a solution. Time passed. He received the United Nation’s highest environmental accolade for his vision. He did a TEDx Talk on his vision. He was chosen European of the Year by Reader’s Digest, among other interesting awards. He assembled a 60-person team of engineers.
And on September 9, 2018, his team launched a 2,000 ft / 600 meter long floating plastic tube with a ten-foot / 3 meter curtain underneath to undergo full-scale sea trials.
How likely is this to make a difference?
It has a much larger opportunity to be successful than I had originally thought. The go-to-study on this was done by Julia Reisser et al. The vertical distribution of buoyant plastics at sea: an observational study in the North Atlantic Gyre was published in 2015 in the journal Biogeosciences, which has a respectable impact factor of 3.7.
The key part of the abstract is this bit:
plastic concentrations drop exponentially with water depth, and decay rates decrease with increasing Beaufort number. Furthermore, smaller pieces presented lower rise velocities and were more susceptible to vertical transport. This resulted in higher depth decays of plastic mass concentration (milligrams/m^3) than numerical concentration (pieces/m^3).
This is well visualized in this chart from the study. The misapprehension I had been under since first hearing about the challenge was that the plastic was more evenly distributed throughout the water column. However, it’s actually concentrated, especially by mass, in the first 50 centimeters or 20 inches of the water.
The device that they are deploying is a 610-meter or 2000-foot floating plastic tube with a 3-meter or 10-foot curtain underneath it. It’s going to float through the water sideways pushed by the wind, forming into a large U-shape with sea anchors keeping it aligned for the most part, catching plastic from that surface volume of water. This is intended to corral the plastic in the surface of the water column and concentrate it, allowing it to be periodically skimmed from the middle of the device by people in boats.
To be clear, Boyan’s vision could have fallen apart at multiple points over the past five years. Reisser’s study or someone else’s could have shown a much more even distribution of plastics through dozens of meters of water column. Plastics could have degraded more quickly in ocean water and sunlight. He could have failed to capture many people’s imaginations sufficiently to engage the funding to achieve his vision. He could have found that his idea didn’t work in the 40 foot / 12 meter version. But so far, his vision has held true.
That said, there are still risks and potential downsides. They appear to have been considered fairly carefully and mostly avoided but there are still failure points, and it’s clear that this is only part of a solution.
Loss of plastic – The device is very slow moving and the current from the device, down the curtain to open water, is expected to not overcome buoyancy of a majority of the mass of plastic. As the mass is concentrated at the surface in more buoyant plastics, the solution is credible.
Sealife capture – The device is very slow moving and there will be a gentle downward current from the device down to the bottom of the curtain. This should enable most surface sea life to escape it. It’s open on one end, open at the bottom and the curtain is solid not a net, so there should be very little fish capture or marine mammal impacts.
Breakup of device – The open ocean has large rollers which are often very high but typically not crashing waves. The flexibility of the device appears sufficient to cope with normal conditions. However, the ocean also has major storms and high winds and the durability of the device is yet to be determined.
Effective capture of plastic mass – A study by Cozar et al, Plastic debris in the open ocean, finds that microparticles of plastic represent a very large percentage of plastic in the ocean and represent the greatest intrusion into biological systems. It’s the microscopic plastic particles in bodies, not the beer can rings on turtles’ necks, which potentially are a much greater impact. The Ocean Capture system will not capture these microparticles, but would prevent larger plastic pieces in the ocean from becoming microparticles. In other words, this is a part of a solution, not a full solution. The overall value is diminished but there is still value.
More expensive – As the saying goes a gram of prevention is worth a kilogram of cure. This is a cure, not prevention. Global efforts to reduce plastics reaching the oceans are going to have a much bigger impact at a lower cost. However, the plastic in the gyres is already there and can’t be prevented by closing the clichéd gate now, so this band-aid has value.
Moving the device – Pulling a 610-meter device with a 10-meter solid curtain through the water sideways with two ships would consume a lot of fuel. Greenhouse gases and other pollutants would be coming out. It’s unclear if a full carbon and pollution accounting has been done. Ocean Cleanup claims in its FAQ that they won’t be towing the devices but letting them drift with the current and having the wind push the device faster so that plastic is gathered. As the gyres are wind-driven, this has at least superficial credibility, but there is strong variance at the detailed points of complex systems. They acknowledge that CO2 emissions would be very large if they did tow the device.
All in all, I’m much more optimistic than I was before looking at the studies and the device in more detail. However, stopping the flow of plastics into the ocean is necessary just as stopping emitting CO2 is necessary. Expensive band-aids only work so well, and what seems reasonable today will not seem reasonable to fund in perpetuity.
Boyan’s vision is coming true and it continues to show value. For an 18-year old’s dream, that’s impressive. For the oceans and the animals in them, if all works out well it will be more impressive.
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