A novel membrane-aerated, membrane-coupled bioreactor (M2BR) was developed to treat wastewater collected during long-term space missions. The M2BR is particularly attractive for long-term space missions because it achieves aeration and biomass separation using approaches that are compatible
with microgravity conditions. Bubbleless gas transfer is achieved in the M2BR using a hollow fiber membrane module with flat sheet configuration; this membrane also serves as a support media for biofilm growth. The counter-diffusion of oxygen and substrates into this biofilm promotes a unique
bacterial stratification compared to conventional biofilms. Nitrifying bacteria and aerobic heterotrophs grow near the membrane surface (aerobic conditions), while denitrifying bacteria and other anaerobic heterotrophs form the outer layer of the biofilm (anoxic conditions). The M2BR is also
coupled to a microfiltration membrane module that achieves complete biomass retention and produces a cell-free effluent. Preliminary results have demonstrated that the M2BR can simultaneously achieve more than 90% COD and 85% total nitrogen removal when treating a synthetic space mission
wastewater. Due to the low C:N ratio of the wastewater expected during space travel, however, additional electron donor is needed to achieve 100% denitrification. In conclusion, the M2BR provides considerable promise as a biotechnology for the treatment of wastewater during long-term space
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