Sunday, 30 October 2011

How is NASA is Turning Urine into Water?

Subtitle: Filtering Pee for Hydration.  From Water World to Today's Space Shuttles

I am a huge science fiction fan.  Everything from Neuromancer, The Time Machine, Hitch hiker's guide to the Galaxy to closer to real stuff like Michael Crichton's NeXt.  I love it enough that I have even tried to pen a couple of short stories myself.  (Let's see how that turns out).

The thing I love about science fiction though is not just fantastic fantasy in the out of this world stories,  but also  the fact that they can predict a future.  On the website technovelgy you can see some of the technology that people have created in the early 20th century to inventions that occur only today.  Things like touch screen tablet computers (first seen in 2001 Space Odyssey) to filtering pee for drinking water.  Before you say, 'Ohhh disgusting!' you have to understand why Kevin Costner aka the Mariner filtered his own pee and why people on the Atlantis the space shuttle are doing it.  Easy answer!  It is efficient, cost effective and prefiltered though your kidneys'.

In Water World the Mariner (half-man, half-fish) lives on earth after the polar ice caps have melted.  On his raft he had a device that filters out his pee.  You might think: why not drink the water around you?  However, it might be easier to filter out the small number of contaminants in urine than filter out the large number of variable contaminants in ocean water.  But the rudimentary technology from Waterworld is here!  Today astronauts filter their pee on the space shuttle Atlantis because it saves both money and space.  To get a four litre jug of water on a space flight it costs 80,000 dollars and the current urine recycler on board uses a lot of energy.  So as the title suggests golden showers can really be a metaphor for real gold in the context of saving money.  The new osmosis system they are developing uses passive filtration (no energy).  The filtered water that the astronauts will drink soon is be cleaner than U.S. tap water.  

In the astronauts and possibly the Mariner's case it is important to delve into the properties of urine.  What are they? Urine consists of 95% water, with the remaining constituents are mainly salt solutions.  These are in order of decreasing concentration urea 9.3 g/L, chloride 1.87 g/L, sodium 1.17 g/L, potassium 0.750 g/L, creatinine 0.670 g/L and other dissolved ions, inorganic and organic compounds (e.g. bile salts and surfactants).   Urine is sterile until it reaches the urethra where gram negative bacteria from outside can go into the pee (which makes it stink).  The physicochemical characteristics: pH 7 (can vary 4.6-8), density of 1.003–1.035 (g·cm−3) and surface tension 55.7 to 62.0 mN/m; mean for group 58.7 mN/m (from 12 people after 24 hours). One interesting note in this paper is that bile salts cause most of the change in the surface tension with the other salts, urea and creatine causing little change to the water surface tension.  This information might help to produce a better filtration system.

Currently, two researchers are conducting this technology assessment: Kennedy Space Center researcher Howard Levine and  Dynamac researcher Michael Roberts to create a forward osmosis bag (FOB).  Basically it works like this: wastewater (e.g. pee) fills the bag and passively transfers through an inner layer, which contains the sugar solution; toxins are left behind as the liquid passes from the outer layer to the inner and the wastewater becomes safe to drink. However, the system has not been perfected yet, and certain toxins can still get through the filters (these might be bile salts since bile acids are potentially toxic to cells).  If the astronauts drink these toxins they can build up in the kidneys over time making the FOB only practical for short journeys.  Editors note:  to fix the problem they might want to use some Carafate (sucralfate), and Questran (cholestyramine) or some other bile acid sequesterants.

Think I am lying?  Check out this demonstration:

By the way HTI the company that makes a similar filtering system has used this technology for rescue missions on earth from Haiti to Hurricane Katrina.  The results are amazing.  See this video.