A recent report I had to do on the viability of NASA's phenomenal budget led me to information about a nanomesh filter they've been using on the space station.
http://www.sti.nasa.gov/tto/Spinoff2008/er_4.html
It seemed impressive to me, though at this point I really have no idea what I'm talking about. All I could glean was that, damn, 99.99% is pretty close to 100%, and 5 gallons per minute with gravity sounds pretty useful.
I just checked their website to see about pricing for you but it's down. Maybe it'll be up when you look.
http://www.seldontechnologies.com/
Good luck and I hope it works out for you. It's really interesting to read about this humanitarian aspect of Special Forces.