A Novel Membrane Bioreactor for Spacecraft Water Recycling

Abstract

The Redox Control Reactor is a new bioreactor design that delivers both oxygen and hydrogen simultaneously through hollow fiber membranes. A prototype is currently being evaluated that is treating an analog urine-based spacecraft wastewater. During initial operation on oxygen only, nitrification rates of 4.5 g/m 2 day NH3-N have been reached, indicating the high transformation rates of the prototype design. Hydrogen supply will be initiated to evaluate the potential for complete nitrogen removal in the Redox Control Reactor through simultaneous nitrification and denitrification. Hollow Fiber Membrane Bioreactors The use of hollow fiber membranes to deliver gases from lumen to external microbial biofilms is an evolving technology for wastewater treatment and reuse. Brindle et al. (1998) used dead end hollow fibers to treat ammonia in a laboratory scale membrane aerated bioreactor and achieved a specific nitrification rate of 5.4 g NH4-N/ m 2 -day. Simultaneous nitrification and denitrification of municipal wastewater were achieved using an air-supplied porous gas permeable membrane, with total nitrogen removals of 1.1 to 3.1 g/m 2 -day (Suzuki et al., 2000), while a nitrification rate of 1.9 g N /m 2 -d was achieved with a hydrophobic flat sheet teflon membrane treating a model domestic wastewater (Yamagiwa et al.,1998). A pilot study was performed using hollow fiber membranes for aeration of municipal sewage, in which attached biofilms created simultaneous aerobic and anaerobic conditions and removed 80% COD and 50 to 75% of total nitrogen (Semmens, 2002). A modified polyethylene membrane was used to treat an artificial wastewater, with a specific nitrogen removal of 4.48 g/m 2 -day (Terada et al., 2003). Recent investigations have also focused on using hollow fibers to supply molecular hydrogen gas for catalysis of hydrogenotrophic microbial reactions. Lee and Rittman (2000) used dead end hollow fibers to achieve high nitrate fluxes of up to 1.0 g /m 2 day NO3-N and 100% hydrogen transfer efficiency. The establishment of good biofilm accumulation, with thicknesses up to 179 um, was attributed to the low frequency of fiber to fiber contact. H2 was applied through microporous hollow fibers and produced nitrate utilization rates of up to 770 g/m 3 -d and a maximum NO3-N flux to biofilm of 2.2 g/m 2 -d (Ergas and Reuss, 2001).