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The ability of iodine to maintain microbial water quality in a simulated spacecraft water system is being studied. An iodine level of about 2.0 mg/L is maintained by passing ultrapure influent water through an iodinated ion exchange resin. Six liters are withdrawn daily and the chemical and microbial quality of the water is monitored regularly. Stainless steel coupons used to monitor biofilm formation are being analyzed by culture methods, epifluorescence microscopy, and scanning electron microscopy. Results from the first two years of operation show a single episode of high bacterial colony counts in the iodinated system. This growth was apparently controlled by replacing the iodinated ion exchange resin. Scanning electron microscopy indicates that the iodine has limited but not completely eliminated the formation of biofilm during the first two years of operation.

Microbial proliferation in the STS potable water system is prevented by maintaining a 2-5 ppm iodine residual. The iodine is added to fuel cell water by an iodinated ion exchange resin in the Microbial Check Valve (MCV). Crew comments indicated excessive iodine in the potable water. To better define the problem, a method of in-flight iodine analysis was developed. Inflight analysis during STS-30 and STS-28 indicated iodine residuals were generally in the 9-13 ppm range. It was determined that the high iodine residual was caused by MCV influent temperatures in excess of 120 °F. This is well above the MCV operating range of 65-90 °F. The solution to this problem was to develop a resin suitable for the higher temperatures. Since 8 months were required to formulate a MCV resin suitable for the higher temperatures, a temporary solution was necessary. Two additional MCV's were installed on the chilled and ambient water lines leading into the galley to remove the excess iodine.

Collapsible bladder tanks called Contingency Water Containers (CWCs) have been used to transfer water from the Shuttle to the Mir and the International Space Station (ISS). Because their use as potable water storage on the ISS is planned for years, efforts are underway to improve the containers, including the evaluation of new materials. Combitherm®, a multi-layer plastic film, is a material under evaluation for use as the CWC bag material. It consists of layers of linear low density polyethylene, ethylene-vinyl alcohol copolymer, nylon, and a solvent- free adhesive layer. Long term studies of the quality of water stored in Combitherm bladders indicate a gradual but steady increase in the total organic carbon value. This suggests a leaching or breakdown of an organic component of the Combitherm.

The Water and Food Analytical Laboratory, at the Johnson Space Center is developing an alternative to EPA Method 625 for analyzing semivolatile organic compounds in water. The current EPA method uses liquid-liquid extraction. The alternative method being developed differs in the sample preparation phase by replacing gravity-dependent liquid-liquid extraction with solid phase extraction (SPE). The ultimate goal is to incorporate the optimum SPE conditions into an automated sample preparation process. The method shows promise with regard to anticipated polar compounds. Fourteen SPE resins and nine elution solvents were compared. For typical analytes encountered by our laboratory, a styrene-divinylbenzene SPE resin and an elution solvent mixture of methylene chloride and ethyl ether were found to give the highest extraction recoveries. A study is in progress to remove water from the extracts before GC/MS analysis.

The Microbial Check Valve (MCV) is a reloadable flow-through canister containing iodinated ion exchange resin, which is used aboard the Shuttle Orbiter as a disinfectant to maintain water potability. The MCV exhibits a significant contact kill and imparts a biocidal residual I2 concentration to the effluent. MCVs in current use have nominal 30 day lives. MCVs baselined for Space Station Freedom will have 90 day lives, and will require replacement 120 times over 30 years. Means to extend MCV life are desirable to minimize resupply penalties. New technology has been developed for fully autonomous in situ regeneration of an expended MCV canister. The Regenerative Microbial Check Valve (RMCV) consists of an MCV, a packed bed of crystalline I2, a flow diverter valve, an in-line iodine monitor and a microcontroller. During regeneration, flow is directed first through the packed I2 bed and then into the MCV where the resin is replenished.

Two simulated spacecraft water systems are being used to evaluate the effectiveness of iodine for controlling microbial contamination within such systems. An iodine concentration of about 2.0 mg/L is maintained in one system by passing ultrapure water through an iodinated ion exchange resin. Stainless steel coupons with electropolished and mechanically-polished sides are being used to monitor biofilm formation. Results after three years of operation show a single episode of significant bacterial growth in the iodinated system when the iodine level dropped to 1.9 mg/L. This growth was apparently controlled by replacing the iodinated ion exchange resin, thereby increasing the iodine level. The second batch of resin has remained effective in controlling microbial growth down to an iodine level of 1.0 mg/L. Scanning electron microscopy indicates that the iodine has impeded but may have not completely eliminated the formation of biofilm.

The ability of iodine to control microbial contamination and biofilm formation in spacecraft water distribution systems is being studied. Two stainless steel water subsystems are being used. One subsystem has an iodine level of 2.5 mg/L maintained by an iodinated ion-exchange resin. The other subsystem has no iodine added. Stainless steel coupons are being removed from each system to monitor biofilm formation. Results from the first six months of operation indicate that 2.5 mg/L of iodine has limited the number of viable bacteria that can be recovered from the iodinated subsystem. Epifluorescence microscopy of the coupons taken from this subsystem, however, indicates some evidence of microbial colonization after 15 weeks of operation. Numerous bacteria have been continually recovered from both the water samples and the coupons taken from the noniodinated subsystem after only 3 weeks of operation.