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. The ambient pressure ICPB reactor exhibited a consistent COD removal efficiency exceeding 90% at a hydraulic retention time as low as 7 hours. The COD removal efficiency in the pressurized system is approximately 90% at a hydraulic retention time of 10 hours.