Osmotic Distillation for the Recycle of Spacecraft Wastewater
Michael J. Flynn, Lance D. Delzeit, Hali Shaw, Tra-My Justine Richardson, Sherwin Gormly, Kevin Howard · 40th International Conference on Environmental Systems · 2010
The osmotic distillation (OD) system is being developed as spacecraft water treatment system capable of recycling urine and humidity condensate to potable standards. This technology uses osmotic distillation followed by reverse osmosis (RO). OD is an isothermal distillation process. It uses the osmotic potential difference between a feed stream and an osmotic agent (OA) to distill water across a hydrophobic membrane. This membrane has pores small enough to allow water vapor to pass but acts as a barrier to the passage of liquid water. An RO system is used to remove the condensed water from the OA as product at the same rate that it crosses the OD membrane. The RO system also reconstitutes the OA. The OD system produces water with non-purgeable total organic carbon (NPTOCs) typically below 3 mg/l when treating human urine and produces water with TOC below 10 ppm when treating a combination of humidity condensate and urine. Total dissolved solids and ammonia are typically below NASA potable specifications. Post treatment with activated carbon or oxidation may be required to address residual odor issues in some cases. The OD system is being developed as an emergency backup to more conventional water treatment systems or as primary water treatment system for shorter missions such as early stages of a Lunar base, extended lunar rover missions, Mars transit missions, near Earth asteroid missions, or LaGrange point “Great Observatory” type missions. This paper provides results of testing of the OD system to date.