Development of a Nitrifying Bioreactor for the Treatment of Wastewater in Long-Term Space Applications

The objective of this study was to evaluate the potential use of hollow fiber membrane-aerated bioreactors for the nitrification of wastewater during long-term space missions. To define the minimum acceptable treatment efficiency for the experiment, the water recovery system (WRS) at Texas Tech University (TTU) was used, which is a small-scale replica (1/20^th) of the WRS at NASA's Johnson Space Center (JSC). The WRS consists of a biological system designed for nitrogen and organic carbon removal, and a post-processing system consisting of reverse osmosis (RO), ion exchange (IE) and UV treatment. The biological portion of the WRS was the focus of this research and contains an anaerobic packed bed (PB) promoting denitrification, and a tubular reactor (TR) promoting nitrification. Biological systems have been deemed promising by NASA for long-term space applications because of their low mass and high energy efficiency. Both the biological portion of the WRS and the AMR utilized an internal recycle; this study analyzed the data from a recycle ratio (RR) of 1:10 (expressed as mL/min of feed to mL/min of recycled effluent). The AMR was operated at RR 10 for a period of 120 days, while the WRS was operated at RR10 for 109 days. The percent nitrification for the AMR (60.7%) was higher than the WRS (52.3%), indicating the possibility of the AMR as a replacement for the TR. During analysis of the two systems, it was noted that the AMR contained denitrifying organisms, supported by the removal of nitrogen and organic carbon (44.7% and 91.9%, respectively). The AMR was not originally designed to operate as a denitrifying reactor, but the data indicated the potential of the AMR operating as a combined carbon-nitrogen removal system. Following the analysis of this data, two more AMR's were built and are currently being evaluated at TTU.