Multimodal biofilm control strategies for spacecraft water systems: Evaluating coatings, nutrient removal, and biocides for improved sustainability

Functional water recovery systems will be a limiting factor for future spaceflight missions traveling beyond low Earth orbit. Previously, microbial communities known as biofilms have clogged valves in the International Space Station (ISS) water recovery system. To prevent part replacement, ensure safe water for astronauts, and enhance sustainability of long-term spaceflight, improved methods of biofilm control are needed. In this study, three approaches were evaluated for their ability to control biofilm alone and in combination. The methods include the use of Sher-Loxane® 800, a commercially available coating, exclusion of phosphorus from the growth medium, and regular dosing with a silver fluoride biocide. These strategies have all been proposed for biofilm control in spacecraft but have not been evaluated together. Further, this research uniquely features a defined multidomain consortium of organisms (a fungus and three bacteria) frequently isolated from the ISS water system. Results indicate that the presence of the coating is a key factor in reducing biofilm accumulation, and that combining all three biofilm control methods reduces accumulation of viable biofilm to just above the limit of detection after seven days of growth. This study presents the potential for controlling biofilm with multiple methods for spacecraft and Earth-based water systems.