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The Microbial Check Valve (MCV) is used on the Space Shuttle to impart an iodine residual to the drinking water to maintain microbial control. Approximately twenty MCV locations have been identified in the Space Station Freedom design, each with a 90 day life. This translates to 2400 replacement units in 30 years of operation. An in situ regeneration concept has been demonstrated that will reduce this replacement requirement to less than 300 units based on data to date and potentially fewer as further regenerations are accomplished. A totally automated system will result in significant savings in crew time, resupply requirements and replacement costs. An additional feature of the device is the ability to provide a concentrated biocide source (200 mg/liter of I2) that can be used to superiodinate systems routinely or after a microbial upset. This program was accomplished under NASA Contract Number NAS9-18113.

Throughout the history of manned space flight the supply of potable water to the astronauts has presented unique problems. Of particular concern has been the microbiological quality of the potable water. This has required the development of both preflight water system servicing procedures to disinfect the systems and inflight disinfectant addition and monitoring devices to ensure continuing microbiological control. The disinfectants successfully used to date have been aqueous chlorine or iodine. Because of special system limitations the use of iodine has been the most successful for inflight use and promises to be the agent most likely to be used in the future. Future spacecraft potable, hygiene, and experiment water systems will utilize recycled water. This will present special problems for water quality control. NASA is currently conducting research and development to solve these problems.

The electrosynthesis of expendable reagents including acids, bases, and oxidants from simple salts or salt mixtures has been demonstrated using a variety of electrochemical cells. A five chambered electrodialytic water splitting (EDWS) cell with bipolar membranes was utilized to efficiently convert sodium sulfate, sodium chloride, potassium nitrate, and potassium chloride to conjugate acids and bases. With the same cell, selective segregation of cations and anions from mixed salt solutions occurred, resulting in relatively pure acids and bases. These results suggest that pure acids and bases can be produced from composite spacecraft brines. Chemical oxidants such as sodium and ammonium persulfate were also synthesized with high current efficiencies by the electrooxidation of salts and acids in a two chambered electrochemical cell.