BBC Story: Urine Recycling System for ISS - Odd Points Explored

[mgb_phys]

Story on the BBC about a urine recycling system for the ISS - it doesn't have a lot of tech details but a few points seemed odd.

It uses distilation which means it needs a centrifuge to simulate gravity. A hand powered reverse osmosis pump on a lifeboat can take water from seawater - wouldn't the same thing be simpler.?

Isn't most of your body's water lost in breathing (especially in a dry air conditioned enviroment). MIR (IFIRC) had a gutter system to collect condensation form the walls.

What's the oxygen supply on the ISS, MIR also electrolysed liquid waste to generate oxygen (while dumping the hydrogen into space). Recycling drinking water while having to ship compressed oxygen cylinders seems unlikely.

Is this just a proof of concept thing for a future longer mission?

 

[Topher925]

I don't have an answer to all your question but as for the life boat hand powered osmosis thing, not its not that simple. Urine contains a lot of more "stuff" than sea water does. A lot of it being biological waste that you do not want to ingest. For example, ammonia. I don't believe you can apply reverse osmosis to urine and get drinkable water.

 

[minger]

Psh, I've seen Surviorman's Les Stroud do the same thing with a couple of rocks, some plastic wrap, and a cup...and the sun.

 

[mgb_phys]

Yes - that's exactly what Nasa are doing, but it requires gravity.

 

[D H]

For some technical details see http://www.nasa.gov/centers/marshall/pdf/104840main_eclss.pdf.

This is not a proof of concept system. It is essential to enable the ISS to host a crew of six (the current contingent is three people). The Water Recovery System recycles water from showers, washing, condensate, and urine. The already-delivered Oxygen Generation System generates oxygen by electrolysis.

 

[mgb_phys]

Ok so most of the recycled water does come from climate control, washing, cooling etc.
And they ship water up to use to generate oxygen anyway.

Given the problem of dealing with filter eating acid crystals and toxic ammonia it would seem to make sense to just dump the urine anyway. But I suppose the purpose of ISS is to test stuff like this.

 

[Proton Soup]

I don't have an answer to all your question but as for the life boat hand powered osmosis thing, not its not that simple. Urine contains a lot of more "stuff" than sea water does. A lot of it being biological waste that you do not want to ingest. For example, ammonia. I don't believe you can apply reverse osmosis to urine and get drinkable water.

you can, it'll take everything out. the membranes might not last very long, but this isn't the real problem with RO. RO produces a huge fraction of waste water. this is fine at home where you can either let the waste go down the drain, or route it to the flower bed.

RO filters are usually multistage, with sediment, carbon, and even anion/cation filters in the prestages. and like this, they produce water as pure or more than distilled. certainly several times more pure than what is necessary to make it potable. but it's a very wasteful process, so not that practical in a closed system.