The process could be more efficient than air-capture systems, Hatton says, because the concentration of carbon dioxide in seawater is more than 100 times greater than it is in air. In direct air-capture systems it is first necessary to capture and concentrate the gas before recovering it.
In reference to the "big ponds" - yes, people are doing this (myself included) but our process relies on using microalgae as the agent of decarbonisation, and our R&D is going into more efficient ways to produce and harvest the microalgal cells. Photosynthesis is still a pretty good way to capture CO2, and microalgae grow the fastest.
I've also wondered about whatever mineralization happens in making sea shells - I understand that's another natural process that fixes CO2, is that something that could be replicated, artificially or through growing a high concentration of little shellfish?
This is straight up wrong. Unless they mean alkalinity, which is carbonate, but not dissolved CO2.
I keep both reef and freshwater aquariums. I have to inject CO2 into my freshwater aquariums to keep the plants happy, and the maximum I can go without killing off the fish is ~30ppm. Given that the PPM of CO2 in air is 4, are they trying to say saltwater has 400PPM of CO2? That would mean ocean water is 0.04% CO2. A wave would have so much foam because of how much carbonation that'd be in the water.
They're doing some funny math.
This is wrong, CO2 is currently 420PPM in Earth's atmosphere.
Indeed, and it has been. Google's Project Foghorn's process was (2014) was based on the same concept.
It's so completely obvious in hindsight. It's amazing how many great ideas share that property.
I'm no chemist, but ... is there something solid that it could be converted to instead? Like baking soda, rather than a difficult to store gas?
Maybe something like this?
https://www.scientificamerican.com/article/desalination-brea...
Wow, I didn't know salinity doubled in the Arabian sea in only 10 years.
Unless the improvements made here are really significant, I don't see how this actually solves anything until we have moved to truly clean energy production.
If you were dumb enough to power it with coal then you'd have net emissions, but put it someplace sunny, power it with solar at 2 cents/kWh and you're paying just $15.40 in energy cost per ton of CO2 absorption. One gallon of gasoline produces 20 pounds of CO2, and there are 2204 pounds in a metric ton, so you could pay for this by adding a surcharge of just 7 cents/gallon.
Of course that's just energy cost, there's also capital cost, and I don't have an estimate for that. But it's not obviously unworkable. Reducing emissions is usually better but I could see this being pretty helpful for cleaning up things that are hard to decarbonize, and once we hit net zero we'll need tech like this already scaling to bring CO2 back down.
https://www.american.edu/sis/centers/carbon-removal/fact-she...
The MIT article presents an expensive strawman alternative, but ignores simpler, cheaper technologies that already exist.
In particular, since CO2 acidifies the ocean, dumping alkaline chemicals into sea water converts the CO2 to inert solids, which precipitate out. At least, that's the theory. Caveats in link.
so basically overeating fish is to be offset by miracle technology. brilliant.
A bipolar membrane (BPM) consists of a polymer membrane full of positively charged groups (the anion-exchange resin) intimately bound to a polymer membrane full of negatively charged groups (the cation-exchange resin). The interface (reminiscent of a p-n junction) is known as a bipolar junction, and acts as an electrode under a sufficiently high potential gradient. They are made out of cheap materials which have been used in ion-exchange resins and membranes since the 60s, but the bipolar membrane process is niche and hasn't been anywhere as highly developed as other electrodialysis membranes. And electrodialysis is fairly niche, and hasn't been nearly as highly developed as membranes for gas separation, desalination, or removal of particulates (ultra- and micro-filtration).
It turned out that electrodialysis is less efficient for seawater desalination than reverse osmosis (the potential drop through the product water becomes really severe if you're trying to produce drinking water from seawater), so electrodialysis was half-abandoned in comparison to RO. Oddly, Japanese companies developed a lot of ED technology to its current state, including ion-selective cation exchange membranes, for producing table salt, since Japan doesn't have the climate necessary for normal salt evaporation. The ion-selective cation resins were developed for removing Mg from seawater for table salt, but are now popular for researchers trying to do lithium separations.
Anyway, while I agree with the authors that BPMs have unresolved challenges (related to efficiency, mechanical stability, and the fact that current membranes are required to be loaded with transition metal catalyst to get a decent water splitting rate at a low overpotential), I don't know that I'm convinced that their approach is better just because they call BPMs "expensive" four times. If we wanted to adjust the pH of a lot of water, we would need, as a guess, roughly the same amount of electrode catalyst surface area, or the same amount of bipolar junction surface area. However, the bipolar junction is made out of commodity polymer resins heat laminated together, while the electrodes in this study are made out of silver and bismuth. If the bipolar membrane is loaded with a metal catalyst, the most common one is iron. I don't see the BPMs being the more costly solution for very long.
For full disclosure, I recently started doing some work on BPMs, but I think the problems associated with it are solvable, especially for applications like this (as opposed to much more challenging conditions like CO2 electrolyzers).