[px43]

~~Yeah, I think carbon recycling can be pretty good. They've been doing it on submarines for a while.~~

(edit: nevermind, I was confused about the submarine thing, the user "idlewords" below has a lot of good commentary about this)

At any given moment, any human is about 18% carbon. Carbon is also pretty important in *carbo*hydrates. Any plants that we would grow would need a ton of carbon. It can be done, but any moon colony will basically always be dependent on getting extra carbon from Earth, so it can never be "self sufficient" in the way that Mars can eventually be.

It is kind of funny that on Earth, we're obsessed with capturing and burying as much carbon as possible, when it's going to be an incredibly valuable resource on the moon, assuming that a bunch of people are gong to want to live there.

[shagie]

Submarines restock food, some air supplies, and... deal with waste.

Food https://youtu.be/bPJUVKizh90

Air https://youtu.be/g3Ud6mHdhlQ (MEA and LIOH for CO2, electrolysis and "candles" for oxygen)

Toilet https://youtu.be/SYFuA3xnkUE?t=985

Nothing is "recycled" as such - and certainly not any of the carbon (you're not eating the carbon captured from MEA or LIOH... or your waste).

[wonderwonder]

Seems like carbon capture and export to the moon is a business that is just short of a billionaire to implement it.

[idlewords]

Submarines don't recycle carbon; they capture CO2 and vent it.

[rtkwe]

Mostly because they don't need to retain it though, a sub doesn't need to reprocess the CO2 into C and O2 but the process can be done. The process is largely the same instead of ejecting it as a waste product continue to break it down into useful products like injecting it into a Sabatier process.

[idlewords]

The Sabatier reactor on the space station broke after processing about a thousand liters of water because deodorant and astronaut urine poisoned the catalyst beds.

Everything is easy to do in theory. Recycling carbon in practice is very, very hard if you don't have plants to help you.

[shagie]

Hypothetically... after you have separated the carbon from the oxygen (discounting the human waste which has a significantly more amount of carbon)... what would you do with it as part of a recycling process in a submarine?

[rtkwe]

In current tech not much comes to mine. Maybe it could be reprocessed into dry graphite lubricant but there's not much need for raw carbon or principally carbon materials in a submarine. That's another reason it just gets tossed there's just not a real use for it. On a hypothetical extraplanetary colony though it's a pretty important material just to keep people alive.

[idlewords]

You can store it as methane and cook with it in the galley.

[rtkwe]

You don't want to be simply reintroducing it into the atmosphere again that would just increase the amount you need to scrub out of the air because now your cycle just reintroduces all the CO2 you remove back into the air along with the stuff the sailors are breathing out. Submarines as far as I can see have basically always used electric cook tops for that reason, at least since they were designed to stay submerged most of the time. UBoats probably didn't because electric power was so limited they probably just didn't cook hot food while submerged.

[shagie]

Its a bit worse than that.

Going CO2 -> C + O2 -> (+ 2x H2) -> CH4...

But the combustion of CH4 is CH4 + 2x O2 -> CO2 + 2x H2O.

The loss of O2 to water means that each time through this removes O2 from the atmosphere which would need to be replenished.

That ignores all the energy losses in the process and requirements...

As to the uboat - https://uboat.net/men/foodstuffs.htm

> The galley was located on the starboard side, between the chiefs' quarters and the wardroom, and was made up of three hotplates and two small electric ovens. It also contained a refrigerator, self-heating soup kettle, provision lockers, and an enamel sink with hot and cold fresh water and hot salt water.

https://maritime.org/tour/cm.php?pano=nr

https://maritime.org/pres/potrack/pots.php

> The custom built pots were designed fit the Edison Type B range/oven built used on the fleet boats.

https://forums.spacebattles.com/threads/pig-boats-fleet-boat...

> Fleet subs of the Gato (SS 212) and Balao (SS 285) classes boasted sizable freezer and refrigerator compartments, and their galleys, though diminutive, were well-equipped, generally with two griddles, a deep-fat fryer, two electric ovens, a hefty electric mixer, and a two-gallon coffee urn. Fleet boats usually boasted an ice cream maker as well, even when lack of space in the galley or crew mess made it necessary to install the machine among the bunks in the crew's berthing space.

(Note the 'deep-fat fryer' bit and the modern sub https://youtu.be/bPJUVKizh90?t=364 )

Do note that submarines were built by the Electric Boat Company founded in 1899. Electric systems were in use since the start.

[idlewords]

Then you can use it to make fizzy drinks.

[shagie]

That's not exactly a closed loop recycling system.

Additionally, flame is very restricted on a sub. You wouldn't be using any sort of methane to cook.

https://qr.ae/prgBKF

https://qr.ae/prgBsh

https://www.answers.com/Q/What_fuel_does_a_submarine_use_for...

[midoridensha]

The idea of using a combustible gas to cook is archaic and really dumb. It's amazing that people are still cooking this way today in many places. We've had better technology for ages.