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In August 1997 NASA/Marshall Space Flight Center (MSFC) began a test with the objective of monitoring the growth of microorganisms on material simulating the surface of the International Space Station (ISS) Temperature and Humidity Control (THC) Condensing Heat Exchanger (CHX). The test addressed the concerns of potential uncontrolled microbial growth on the surface of the THC CHX subsystem. For this study, humidity condensate from a closed manned environment was used as a direct challenge to the surfaces of six cascades in a test set-up. The condensate was collected using a Shuttle-type CHX within the MSFC End-Use Equipment Testing Facility. Panels in four of the six cascades tested were coated with the ISS CHX silver impregnated hydrophilic coating. The remaining two cascade panels were coated with the hydrophilic coating without the antimicrobial component, silver. Results of the fourteen-month study are discussed in this paper.

Pretreatment of urine using Oxone® and sulfuric acid is baselined in the International Space Station (ISS) waste water reclamation system to control odors, fix Ammonia and control microbial growth. In addition, pretreatment is recommended for long term flight use of urine collection and two phase separation to reduce or eliminate fouling of the associated hardware and plumbing with urine precipitates. This is important to the ISS application because the amount of maintenance time for cleaning and repairing hardware must be minimized. This paper describes the development of a chemical pretreatment system based on solid tablet shapes which are positioned in the inlet urine collection hose and are dissolved by the entrained urine at the proper ratio of pretreatment to urine. Building upon the prior success of the developed and tested solid Oxone tablet, a trade study and tests were completed to confirm if a similar approach would be appropriate for the sulfuric acid injection method.

The Space Station Temperature and Humidity Control Condensing Heat Exchangers will be utilized to collect and remove atmospheric water vapor generated by the metabolic and hygienic activity of crew members. The porous hydrophilic coating within the heat exchangers will always be wet. Cabin air will continuously flow through the heat exchangers during system operation which makes them a potential site for microbial colonization. This paper summarizes the findings from an ongoing study which evaluates biofilm formation on wet hydrophilic coated panels compared to panels to which microbial control measures have been applied. The control measures evaluated are an antimicrobial agent within the coating and periodic drying.

The Space Station Temperature and Humidity Control Condensing Heat Exchangers will be utilized to remove and collect atmospheric water vapor generated by the metabolic and hygienic activity of crew members. The porous hydrophilic coating within the heat exchangers will be continually moist and in contact with a steady flow of cabin air which makes them susceptible to microbial growth. This paper summarizes the findings from an ongoing study to evaluate biofilm formation characteristics and microbial control techniques for the Space Station Condensing Heat Exchangers (CHX). This ongoing study examines whether the CHX's are susceptible to performance degrading microbial colonization with microbial challenge testing under simulated system environmental conditions. Furthermore, the three candidate microbial control approaches of periodic heating, periodic drying and incorporation of an antimicrobial agent, into the hydrophilic coating are evaluated.

Space Station Freedom uses a semi-closed loop recirculating waste water system to regenerate potable water. A specific series of depth and membrane filters can be employed prior to the waste water holding tank to eliminate bacteria at the earliest portion of the Water Processor. Several advantages accrue by using a cold sterilizing method for microbial control. This methodology i) reduces the weight and power requirements needed for a heat sterilizer and exchanger, and ii) significantly reduces biocorrosion and biofilm associated problems. A series of six filters and a two component resin bed was used to process a mixture of laundry water, shower water, and urine distillate in a ratio of 63:28:9 by volume. The final effluent was free of bacteria when grown on R2A agar. Gravimetric analysis was performed on 100 ml of downstream effluent from four filters and compared to the raw water.