Included in NASA’s last space shuttle mission to the International Space Station is a novel filtration bag that uses forward osmosis technology to clean water.
Project researchers hope to be able to turn regular old urine into a refreshing beverage, and the bag already filters everything but urea. The team hopes to add a carbon filter to the bag to overcome this problem.
More from the Forward Osmosis Bag (FOB) project page:
Forward osmosis is a low-resource water treatment technology that can be ideal for spaceflight applications. It utilizes a semi-permeable membrane and a liquid osmotic concentrate to convert non-potable water into a liquid that is safe for consumption. Buoyancy-driven convection and concentration polarization are physical phenomena known to affect membrane performance in a unit gravity environment. Concentration polarization is the build up of a concentration gradient of ionic species, or other solutes, on the surface of the semi-permeable membrane. In 1 g environments temperature driven buoyancy effects tend to disrupt concentration polarization and minimize its effect. In microgravity this buoyancy-driven mixing does not occur. It is possible that if this happens the concentration gradients will build up to an extent that the process will not work or the production rate will be significantly reduced. Performance in a microgravity environment can be modeled, but is difficult to predict. The absence of buoyancy-driven convection in microgravity suggests that mass transport will be dominated by diffusion, slowing the rate of permeate production across the membrane. Conversely, a reduction in concentration polarization, as hypothesized by the Commercial Off The Shelf (COTS) device manufacturer, may increase the rate of permeate production.
A critical component affecting membrane performance will be the efficiency of membrane wetting during the initial charging of the FOB device. Some minimal air entrainment is expected in the non-potable ?challenge? fluid. Two-phase fluids are prone to form non-homogeneous foams in microgravity that may inhibit membrane wetting or reduce the effective wetted surface area of membranes. This FOB membrane is highly hydrophilic and is expected to wet thoroughly even in the presence of a non-homogeneous foam.
As a part of the FOB-1 protocol, one set of three osmosis bags will be mechanically mixed/agitated by a crewmember while a second set of three osmosis bags will simply be charged with fluids and then remain quiescent. The hypothesis for testing in the FOB-1 experiment is that mechanical agitation will not affect the performance of the membrane as measured by membrane flux rate and/or wetted surface area after a six-hour exposure interval. Any detrimental effects of a non-homogeneous two-phase fluid contacting the membrane will be overcome by the highly hydrophilic nature of the membrane material.
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