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IsaacKuo
2012-Nov-27, 12:11 AM
I'm pondering a hard SF setting in the 22nd century, which includes orbital colonies. Food and air is provided by aeroponic gardens. Water is efficiently recycled via air conditioning and waste processing.

But I'm wondering about salt. Here on Earth, salt mines and sea salt are plentiful sources, so I suppose little or no R&D has been done on salt recycling from laundry/waste. But this may be important for space stations, BEO spacecraft, and space colonies.

Does anyone know of research in this area? My crude Google searches come up empty.

My guess is that the low hanging fruit is recovering salt from sweat. So if nothing else, does anyone have any idea how much salt intake ultimately ends up in sweat, vs urine and solid waste? Also, how hard would it be to remove the urea and other unpleasant contaminants?

Thanks!

Jens
2012-Nov-27, 01:43 AM
My guess is that the low hanging fruit is recovering salt from sweat. So if nothing else, does anyone have any idea how much salt intake ultimately ends up in sweat, vs urine and solid waste? Also, how hard would it be to remove the urea and other unpleasant contaminants?


I'm just guessing here, but as you said, on the earth salt is plentiful. So our technology for recovering salt is usually the opposite, i.e. how to get pure water without salt. Though that means that you are also separating the salt. I know that boiling water and then condensing it is a way to get salt from the water. So I don't think it's a particularly difficult process. The sweat will make humidity in the air, and you have the urine, so you'll want to recycle the urine into clean water, which means taking out the salt, right? So on the ISS, if they can process urine back into clean water, I think that means automatically that they can extract the salt.

JustAFriend
2012-Nov-27, 03:02 AM
uh.... read Dune.

As Frank Herbert did, you don't have to go into every last detail about the process.
(unless there is some point in your story that hinges on it)

swampyankee
2012-Nov-27, 03:02 AM
I'm just guessing here, but as you said, on the earth salt is plentiful. So our technology for recovering salt is usually the opposite, i.e. how to get pure water without salt. Though that means that you are also separating the salt. I know that boiling water and then condensing it is a way to get salt from the water. So I don't think it's a particularly difficult process. The sweat will make humidity in the air, and you have the urine, so you'll want to recycle the urine into clean water, which means taking out the salt, right? So on the ISS, if they can process urine back into clean water, I think that means automatically that they can extract the salt.

Assuming "salt" means NaCl, urine is a bit more complex than salty water (see this pdf: NASA CR-1802 (http://franklin.chem.colostate.edu/diverdi/C431/experiments/high_pressure_liquid_chromatography/NASA%20CR-1802%20urine.pdf)).

IsaacKuo
2012-Nov-28, 05:06 PM
Thanks for the replies! Sorry it's taken me a while to reply back...


uh.... read Dune.
As Frank Herbert did, you don't have to go into every last detail about the process.
(unless there is some point in your story that hinges on it)
I'm mainly curious for its own sake.

But it could be a nice story detail, also. The thing is, demand for salt recycling may be low enough that even this low hanging fruit is ignored in favor of simply using salt as a consumable. This depends on consumption rates, which I'm also unfamiliar with. The main character has set off on a 9+ year journey, but without any special stockpiles of supplies prepared. This makes her situation vaguely similar to that of the handful of interstellar missions (which did have carefully prepared supply stockpiles, but with an extremely limited mass budget).


I'm just guessing here, but as you said, on the earth salt is plentiful. So our technology for recovering salt is usually the opposite, i.e. how to get pure water without salt. Though that means that you are also separating the salt. I know that boiling water and then condensing it is a way to get salt from the water. So I don't think it's a particularly difficult process. The sweat will make humidity in the air, and you have the urine, so you'll want to recycle the urine into clean water, which means taking out the salt, right? So on the ISS, if they can process urine back into clean water, I think that means automatically that they can extract the salt.
Other than water, urine's main content is urea--which results in the extremely unpleasant ammonia taste/smell. Sweat has a high salt content compared to the unpleasant contents. Still, it would be recovered from laundry or washing water, where sweat is only part of the contents.

HenrikOlsen
2012-Nov-29, 06:06 PM
If you're going for a closed cycle, the urea's crucial for fertilization, the salt is crucial for basic survival, as cells will die without the sodium, basically there's going to be no metabolic byproducts that won't be needed.
If you use the sweat and urine for growing plants and pick the right combination of plant then you can ignore most of the other details.

IsaacKuo
2012-Nov-29, 08:23 PM
If you're going for a closed cycle, the urea's crucial for fertilization, the salt is crucial for basic survival, as cells will die without the sodium, basically there's going to be no metabolic byproducts that won't be needed.
If you use the sweat and urine for growing plants and pick the right combination of plant then you can ignore most of the other details.
Yes, but there's a qualitative enjoyment factor to having salt, rather than merely ingesting sufficient sodium content in food. If human waste is recycled back into the food via aeroponic nutrient absorption, it may be good enough for survival but the humans surviving on this diet may still gripe about it.

I figure the general cycle is for waste to filtered/distilled for potable water, with the rest filtered and processed for aeroponics. This processing would be some combination of mechanized processing (such as to sterilize it) and microbes.

In addition to processing out water, there would also be optional fluid processing to gather ammonia and methane. Ammonia has various uses, and methane might be further processed into 3D printer feedstock and/or alcohol fuel.

JohnD
2012-Dec-06, 06:13 PM
Isaac,
You can't have searched far.
A Google for "NASA water recycling salt" gets 6 million hits, with this top hit:
http://www.nasa.gov/mission_pages/station/research/benefits/Water.html#
about using the ISS recycler for on Earth applications
"students across the world will sample water in their communities and conduct experiments to learn about our planet's acidity levels, water salt content, and various water treatment, disinfection and salt removal method"

This hit even gives you the name of a company doing this work:
http://www.nasa.gov/mission_pages/station/research/experiments/FOB.html
Hydration Technologies Inc (HTI), Albany, Ontario, Canada
Kennedy Space Center, , FL, United States

Ask NASA?
JOhn

NEOWatcher
2012-Dec-06, 06:18 PM
Isaac,
You can't have searched far.
The problem is that I don't think that answers Isaac's question.

Sure; there's been tons of research to pull stuff out of water to make it clean. But; there's not much out there as to whether the "gunk" pulled out can easily be processed or seperated into useful things like a non-toxic salt.

JohnD
2012-Dec-07, 10:10 AM
Ah! You want the salt, not the water!

See: www.krebs-swiss.com/salex.pdf for commercial salt purification processes.
and
nzic.org.nz/ChemProcesses/production/1H.pdf


The Seawater Greenhouse project sells the salt extracted as "gourmet sea salt"!
http://blogs.ei.columbia.edu/2011/02/18/seawater-greenhouses-produce-tomatoes-in-the-desert/

John
PS You may need to copy those links to PDF files into your address line for them to work

Ivan Viehoff
2012-Dec-07, 12:13 PM
Ah! You want the salt, not the water!

See: www.krebs-swiss.com/salex.pdf for commercial salt purification processes.
and
nzic.org.nz/ChemProcesses/production/1H.pdf

Trouble is that the purification processes require chemical feedstocks, which are equally not to hand on the space station.

But basically I think that salt simply extracted from human wastes, and sufficiently heat treated to remove organic contaminants, will not contain excessive toxic metals, because why would we have toxic levels of metals going into the waste in the first place? Sea salt is a cocktail of metals and cations, but we can eat that.

IsaacKuo
2012-Dec-13, 06:49 PM
Thanks for the additional thoughts!

Trouble is that the purification processes require chemical feedstocks, which are equally not to hand on the space station.

But basically I think that salt simply extracted from human wastes, and sufficiently heat treated to remove organic contaminants, will not contain excessive toxic metals, because why would we have toxic levels of metals going into the waste in the first place? Sea salt is a cocktail of metals and cations, but we can eat that.
Would simple application of heat remove urea? That's the main contaminant I'm worried about, since it would be extremely unpleasant--especially in cooking, due to ammonia generation.

Or would it be better to do something to catalyze the breakdown of urea into ammonia and carbon dioxide? (NH3 and CO2 are both gases in conditions where sodium chloride is solid, so they're trivial to separate).