Sterilization Tests Involving the Addition of Ag to Water Recovery Systems

Microbial control is crucial during the time a water recovery system is shut down—in particular, the control of silver concentrations during start-stop operations and residual silver concentrations and microbial counts during the time the system is nonoperational. Using a ground demonstration model of the Gateway condensate water recovery system co-developed by JAXA and Kurita, we evaluated the stability of silver concentrations and the extent of microbial contamination in effluent through repeated testing undertaken over three years. The testing confirmed that it was possible to maintain stable silver concentrations even during start-stop operations. However, we observed contamination by Ag-resistant bacteria even at these stable silver concentrations. Whether this type of microbial contamination, a common phenomenon on the ISS, may also occur on future manned spacecraft, is unknown. However, our preliminary testing suggests this issue may be solved by exposing the system to contact with elevated silver concentrations for a certain period, then flushing the system.