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System configurations of water recycling for space use have been continued through theoretical and experimental studies. The water recycling system plays a central role in a Closed Ecological Life Support System (CELSS) which offers necessary environment and life styles in closed environment such as space stations, lunar bases, etc.. Membrane technology is a possible candidate for purifying waste water produced by crew use facility, plant cultivation facility, etc. In considerations of the system compactness realizing energy saving, membrane distillation has been revealed to be a suitable purification process. Ground experiments has been performed using membrane filtration processes and membrane distillation process. Thermopervaporation technology with hydrophobic membrane is utilized in the distillation process. The energy saving is achieved by thermal return of condensation energy.

Conceptual studies of closed ecological life support systems (CELSS) carried out at NAL in Japan for a water recycle system using membranes1) are reviewed. The system will treat water from shower room, urine, impure condensation from gas recycle system, and so on. The H2 O recycle system is composed of pre-filter, ultrafiltration membrane, reverse osmosis membrane, and distillator. Some results are shown for a bullet train of toilet-flushing water recycle equipment with an ultrafiltration membrane module. The constant value of the permeation rate with a 4.7m2 of module is about 70 1/h after 500h of operation. Thermovaporization with porous polytetrafluorocarbon membrane is also proposed to replace the distillator.

A wet oxidation system will be useful in CELSS as a facility to treat organic wastes and to redistribute inorganic compounds and elements. However at rather higher temperatures needed in this reaction, for instance, at 260 °C, only 80% of organic carbon in a raw material can be oxidized, and 20% of it will remain in the liquid mainly as acetic acid, which is virtually non-combustible. Furthermore, nitrogen is transformed to ammonium ions which normally cannot be absorbed by plants. To resolve these problems, it becomes necessary to use catalysts. Noble metals such 33 Ru, Rh and so on have proved to be partially effective as these catalysts. That is, oxidation does not occur completely, and the unexpected denitrification, instead of the expected nitrification, occurs. So, it is essential to develop the catalysts which are able to realize the complete oxidation and the nitrification.