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An aerobic pressurized bioreactor system to treat grey water under microgravity conditions has been developed. The treatment system consists of a packed bed bioreactor and an oxygenation device attached to an external re-circulation line. The membrane module provides bubble-free oxygen, at very high concentrations and transfer efficiency. Mass transfer characteristics of the oxygenation module have been studied. Oxygen mass transfer in water is described using a resistance-in-series model. A generalized mass transfer correlation that predicts the oxygen mass transfer coefficient has been developed. Experiments have been conducted to study the nitrification of grey water at various residence times.

Biological processing of grey water in space presents serious challenges, stemming mainly from microgravity conditions. Immobilized cell packed bed bioreactors (ICPB) have been used extensively for the treatment of wastewater on earth and can provide solutions to problems associated with microgravity. In this study two bench scale ICPB bioreactors were operated using synthetic grey water with the objective to develop a gravity independent system. Both reactors were packed with plastic flakes having a surface area of approximately 20 cm2/g, inoculated with activated sludge and fitted with an internal recirculation line to induce mixing and enhance oxygen transfer in the packed bed. One system was operated under ambient conditions with air supplied directly through a bottom port and the second was operated under 20 psi gauge pressure in order to achieve high dissolved oxygen concentration and overcome the problem of phase separation associated with microgravity conditions.