Humidity Condensate Stabilization Using an Engineered Biologically Active Storage Tank

Abstract

Water recovery on ISS reduces resupply costs. Humidity condensate (HC) is a major source of available water on ISS but contains both organic and inorganic contaminants. Organic carbon and nitrogen in the HC can support microbial growth. Microbial growth in the HC storage tank has been documented and this growth has caused operational issues in the past. One possible solution to prevent excess growth and stabilize the humidity condensate to prevent downstream growth is to engineer a storage tank that will facilitate the oxidation of C and N, but prevent biomass shedding and growth downstream. A micro-gravity compatible membrane aerated bioreactor could serve as the HC feed tank and support waste stabilization. The stabilization would not only prevent downstream operational issues but would also reduce the loading on the mixed beds and catalytic oxidizer. We evaluated the performance of a gravity independent MABR treating HC over 7 months of operation. A range of loading rates from 2 C/d to 15 C-d, corresponding to organic carbon loadings from 800-6200 mg/d and a range of organic nitrogen loading from 130-1300 mg/d. Results indicated that the MABR was able to significantly remove organic carbon (>80%), oxidize organic N, and lower the pH with only minimal consumables (O2).