How NOT to clean the ocean, and how to do it better
I came across a post at Core77 about a concept design for a device to clean up the Pacific Trash Vortex, a region of the north Pacific Ocean that seems to be gathering garbage, particularly plastic, where global ocean currents converge. Unfortunately, it’s a really bad design. I will sketch a solution that I think is much better.
The Pacific Trash Vortex is an interesting phenomenon that no one really saw coming till the 1980s, but, in hindsight, seemed rather obvious. Floating garbage will be carried by currents. Any gyre where several such currents meet will result in collections of garbage. This garbage eventually starts to poison the water and the wildlife that lives in it.
The idea behind the design in the Core77 post is that a device slowly wanders through the Vortex, collecting garbage in its net. When it’s full, it gets pulled up to a “mothership,” emptied, and then sent back for more.
My disdain for this design caused me to post about it on Google Plus. The ensuing discussion got me thinking more about it, and that motivated me to post about it here. I should note that some of the points I make here are based on comments posted by others on G+. Rather than reproduce their names here to give them credit, I will just refer you to my G+ post (linked above) which shows who everyone is.
Let’s start with the problems in this design.
First, most ocean-going organisms (and vessels) have some kind of control surfaces, even if it’s just an asymmetry of general shape. That’s because one needs to stabilize oneself with respect to cross-currents and inertial forces. The only way to do that, that I can see, with this design, is to pivot the thrusters extending from the front collar of the thing. Except that, without knowing about the actual dynamics of the thing, it’s not clear to me that using the thrusters will be an efficient solution. Indeed, I suspect it will be terribly inefficient. And the last thing we need if for a device like this to be unnecessarily inefficient.
Second, what happens to the garbage when the device is full, and it’s emptied into the “mothership?” So far, all you’ve done is gotten it out of the water. While that’s a good start, you’re still not out of the woods. Presumably, the mothership would lug the garbage back to terra firma, where it would be processed. That will itself have an environmental impact. And considering that, by some accounts, the size of the Pacific Trash Vortex is comparable to the USA, I can imagine it will take quite a few trips to clean the Vortex up to any significant degree. Remember, too, that more trash is always arriving at the Vortex from all over the Pacific Rim. For this design to make sense at all, one would have to have enough of these devices, and enough motherships, to pull the garbage out of the water faster than it accumulates. But all this design does is move the garbage around without actually doing anything with it; and it does so at some environmental cost. That doesn’t really sound useful to me. Clearly, systems thinking was not on the designers’ minds when they concocted this thing.
Third, it is suggested that some kind of irritating sonic signal will be used to keep fish and other marine life out of the device. Obviously, that’s a concern. These submarine vacuums are probably at least the size of pick-up trucks if not much larger. We don’t want to be killing the ocean life that happens to wander into them by mistake. But the sonic signal thing doesn’t wash. Sound is already considered a source of pollution under water. Sounds made by boats and other machinery may already be damaging submarine ecosystems. Do we really want to go down that road? And which sounds will work on which organisms? And will some sounds repel some organisms but attract others? I just can’t see the sonic thing working out at all.
So, let me suggest an alternative design, which I came up with in a matter of minutes – so it’s not very polished – that I think will actually do the job much better.
Build a massive floating platform and float it into the Vortex. The facility will collect garbage from the water and process it directly on-site, thus generating usable products and raw material rather than garbage to be transported elsewhere.
The platform will generate its own power via a combination of ocean thermal energy (OTEC) and solar energy (both PV for electricity and solar thermal for hot water). It will probably need lots of electricity. The convergence zone for the garbage seems to be at a latitude comparable with the southern USA. This suggests an area of medium to high insolation – and therefore suitable as a solar power source, and an area with a good vertical water temperature differential to run the OTEC system.
The platform will be large enough to contain greenhouses, and maybe even grazing land for small animals like rabbits and goats, for growing food for those who work there, thus minimizing the number of cargo transports that will add to the system’s environmental impact. These green areas will also act as green “roofs” to help insulate the living areas of the platform. Obviously, waste will be recycled on-site too.
A substantial amount of heat will be generated by the machinery and the biomass on the platform. Areas of the platform will be designed using Passivhaus design principles to keep ambient heat out, and also use that internal waste heat for other purposes (e.g. pre-heating water).
The OTEC system itself will require a structure extending from the surface down to quite a depth. That same structure can be used as a spine on which waste collection units will be attached. The only reasonable way to collect garbage is just suctioning water and straining the garbage from it. Once filtered of garbage, the water is used by the OTEC system to generate electricity.
This leaves the fish problem. I’m not sure how to deal with that, but I think a number of different measures will be needed (i.e. there’s no silver bullet). If the suction is mild enough (and made up for by the rather massive size of the installation and the number of input vents it would have), then we might consider using light and scent rather than sound. Light, especially at depth, could very well keep some organisms away. A scent of some predator species might also work. The system could be designed so water containing scent will very quickly be sucked into the system, where the scent chemical can be removed and reused. It might even be useful to actually use large predator organisms – sharks for instance as deterrents to other organisms. The system could be designed so that the sharks are too powerful to be suctioned into it, yet they will eat anything that’s alive near the inlets. There might even be solutions to this problem using magnetic fields that may disorient some organisms. Or perhaps a particular maze-like shape will discourage organisms. In any case, what I’m saying here is that there are probably a wide variety of solutions to keep organisms away from the inlets. I don’t know enough to offer a solution I think would work, but I do know enough to believe such solutions exist.
A small scientific station will also be located on the platform. The station will accommodate scientists who will study the phenomenon of the Vortex, its contents, its growth, and its impact on the marine ecosystem.
Finally, we get to the garbage itself. Rather than ship garbage, the platform would act as a manufacturing facility, turning the garbage into useful products. Indeed, some of the manufactured goods could be used directly on the platform itself. Perhaps it could manufacture recycled plastic bottles or containers. Perhaps it could use the sea water itself, and concentrate sunlight on a slurry of water and garbage to make it decompose into more easily manufactured materials. Whatever is done, the point is that the material shipped from the platform would be usable, not garbage.
There’s a lot of open questions here. I did about 10 minutes research while writing this post. I can’t even decide if the idea is feasible.
But it’s not impossible. And it has the potential of being a serious solution to the problem of the Pacific Trash Vortex. (And the other trash vortices – the one in the Pacific isn’t the only one.)