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Water is recycled on Space Station Freedom (SSF) to avoid the high logistical cost of fresh water resupply. The water system produces potable water from humidity condensate, wash water, fuel cell water transferred from the shuttle, and urine. The processes include vapor compression distillation of urine, heat sterilization, sorption beds, organics oxidation, gas-liquid separation, filtration, and biocide addition. Treated water quality is monitored by a Process Control Water Quality Monitor (PCWQM), which reports water quality to the SSF data management system. Specifically, the PCWQM is an untended, continuous process water quality monitor which measures conductivity, pH, Total Organic Carbon (TOC), temperature, and iodine biocide concentration. TOC is measured by converting organic carbon into CO2 by UV oxidation and using a photometric cell to determine the quantity of gas. Conductivity is measured using a 1000 Hz conductivity cell, compensated for temperature.

Space Station Freedom's water reclamation system requires on-line monitoring to verify acceptable quality for delivery to tanks supplying the crew's potable and hygiene water needs. Total organic carbon, pH, conductivity, temperature, and residual iodine concentration in the effluent from the water processor will be continuously monitored by the Process Control Water Quality Monitor (PCWQM). This paper reports PCWQM analytical system development progress.

Space Station Freedom's potable water recycling system will use iodine biocide. A process control water quality monitor will continually measure potable water parameters, including the 2.0 to 6.0 mg/l iodine concentration range. The iodine sensor will be a photometric flow cell that measures iodine's 465 nm radiative absorption band and reports iodine concentration. The expanded ECLSS Preliminary Operational System Test included prototype iodine sensors. A solid state iodine sensor will meet power, weight, reliability, and maintainability requirements associated with the station's redesign. This paper discusses solid state photometric iodine measurement theory and engineering considerations and presents preliminary LED-based sensor test results.

On-line monitoring of the effluent from the Space Station Freedom (SSF) water reclamation process determines acceptable quality for delivery to tanks supplying the crew's potable and hygiene water needs. TOC, pH, conductivity and iodine (biocide) are continuously monitored by the integrated, computer-controlled Process Control Water Quality Monitor (PCWQM). This paper describes the development of the system with emphasis on membrane gas-liquid separation and reagentless oxidation necessary to adapt standard TOC analysis to the unique requirements of the space environment.