Urine Processing for Water Recovery via Freeze Concentration

Resource recovery, including that of urine water extraction, is one of the most crucial aspects of long-term life support in interplanetary space travel. This paper will consequently examine an innovative approach to processing raw, undiluted urine based on low-temperature freezing. This strategy is uniquely different from NASA's current emphasis on either ‘integrated’ (co-treatment of mixed urine, grey, and condensate waters) or ‘high-temperature’ (i.e., VCD [vapor compression distillation] or VPCAR [vapor phase catalytic ammonia removal]) processing strategies, whereby this liquid freeze-thaw (LiFT) procedure would avoid both chemical and microbial cross-contamination concerns while at the same time securing highly desirable reductions in likely ESM levels. The involved freeze concentration methodology is a low energy process that focuses on the nucleation of pure ice crystals followed by a ripening effect of those crystals and subsequent washing to achieve high extraction efficiencies. A theoretical water recovery value of approximately 88% has been determined based on the eutectic points of the expected urine constituents. Overall, this research paper will focus on several aspects of freeze concentration, including an overview of the basic technology and its various pragmatic applications, as well as a theoretical comparison of model percent recovery rates relative to observed experimental operational values. Detailed testing results will also be presented to confirm the observed low-level migration of inorganic, organic, and biological contaminants into the product water.