Optimizing the Ion Exchange Process for Purification of Spacecraft Wastewater

Separate cation and anion ion exchange (IX), coupled with vacuum-assisted or gas-sweep desorbtion of dissolved carbon dioxide gas, is routinely utilized in terrestrial applications to increase IX bed life by reducing inorganic carbon loading. Successful application of this mature industrial process to spacecraft wastewater processing has the potential to significantly reduce IX bed volume when compared to current mixed-media IX beds. However, potential complications that could offset these benefits include production of free gas and low pH downstream of the cation exchange bed. The purpose of this work was to: (1) Determine the magnitude of these complications, (2) Measure the inorganic contaminant removal effectiveness of Amberjet UP1400 Strong Acid Cation (SAC) and UP4000 Strong Base Anion (SBA) exchange resins, and (3) Quantify the carbon dioxide removal effectiveness of a commercial off-the-shelf membrane contactor (MC) using vacuum-assist. Test results showed: (1) Amberjet UP1400 Strong Acid Cation (SAC) and UP4000 Strong Base Anion (SBA) ion exchange (IX) resins effectively removed all measured inorganic contaminants prior to bed breakthrough, (2) the configuration of a cation IX (CIX) bed followed by a membrane contactor (MC) for vacuum desorption of carbon dioxide removed an average of 91% of the inorganic carbon from the process stream, and (3) there was no measurable adverse effect on the materials of construction. These results indicate that the imposed design challenges are minimal, and that this process can be incorporated into spacecraft wastewater processing applications.