New Technologies for On-Line Water Quality Monitoring 932181
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. Iodine is measured using a solid state, LED-based photometric cell. Temperature is measured directly using an integrated circuit sensor (AD590) mounted in a thermal well. pH is measured using an ISFET, calibrated using solid phase standards. The analytical methodology, hardware description, and results of testing simulated spacecraft water are presented.