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Water recycling systems have been studied at Hitachi using thermopervaporation technology for space use for about ten years. According to the studies this method is a good candidate for space application from the viewpoint of good water quality, system compactness and microgravity adaptability. In this paper we discuss (1) fundamental characteristics (2) temperature distribution and (3) effect of volatile substances of membrane distillation by thermopervaporation method from both theoretical and experimental point of view.

The recovery of important minerals, salt (NaCI) and potassium (K), in a closed system, namely CELSS is discussed. NaCI is needed for humans, but is potentially harmful to plants. Salt is recovered after wet oxidation of urine. Since Na and K have similar chemical and physical properties, their recovery or separation may require sophisticated methods. Na, CI and K ions are separated from other ions by electrodialysis with univalent selective ion-exchange membranes and then NaCI is obtained separately by a crystalization process. Preliminary experiment on crystalization of NaCI-KCl mixed solutions showed a good separation result.