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REMOVAL OF SALTS FROM URINE BY ELECTRODIALYSIS USING A BATCH RECIRCULATION SYSTEM. N. E. Gordils and G. Colуn.  Dept of Chemical Engineering, Univ of Puerto Rico, Mayagьez.

     Humans need food, oxygen and water for their survival.  However, in space these basic necessities are not readily available and the cost involved in supplying them from the earth is expensive and impractical for long time space missions.  The National Aeronautics and Space Administration (NASA) has developed a project in which food, oxygen, water and human wastes can be recycled and then used to support a person.  In the Controlled Ecological Life Support System (CELSS), urine is recycled as a fertilizer for the plants that grow under hydroponic conditions. 

     The scope of the research was the recovery of sodium chloride from human urine, using an electrodialysis cell coupled with ion selective membranes.  Data was obtained at constant applied voltage and at constant current density.  Emphasis was given to the fouling process.

     From the results obtained, the initial rate of NaCl removal was correlated as a power function of the applied voltage if operated at constant voltage.  If operated at constant current density, the initial rate of NaCl removal was estimated by a power function of current density.  The percentage of NaCl removal was calculated with the use of ion chromatography equipment.  From the acquired data, electrodialysis with batch recirculation at constant applied voltage yields higher values of NaCl removal with approximately 94 % (for E = 7.5 V and U = 0.083 m/s).  On the other hand, at constant current density, the higher percentage of removal was 73 % (for i = 43 A/m² and U = 0.083 m/s).  Membrane fouling was always observed due to the strong affinity of the urochromes of urine for the ion selective membranes.  Impedance measurements showed that the anion membranes were the most affected.

     (Supported by NASA:  NAG10-0257.)