Design analysis and validation of an altered gravity biofilm reactor for simulating biofilms in space

Abstract

Biological growth within spacecraft has posed a challenge to human spaceflight since the first long-term missions to space began. Biofilms, a surface attaching biological mass of bacteria and fungi, have clogged space station water systems since we sent up the first space stations. Skylab, the Russian Mir program, and the International Space Station suffered system failures due to biofilm growth within water systems. These failures required system cleaning and filter replacement to remain functional, a solution that increases in cost and difficulty as humanity seeks to return to the moon and travel beyond it. To prevent biofilm growth within these systems and develop cleaning and operating procedures to manage growth, tools are needed to simulate these systems on the ground. In this work, a novel tool is developed for simulating many of the conditions found within these water systems, such as altered gravity and nutrient limitation, while being able to evaluate the growth of these biofilms. This system is called the altered gravity biofilm reactor (AGBR). The AGBR system is designed to produce altered gravity while allowing biofilms to be grown and quantified. To evaluate if low-shear modeled microgravity is being produced, computational fluid dynamics (CFD) simulations were conducted to understand the fluid environment within the AGBR. These simulations were then compared to results obtained using particle imaging velocimetry (PIV) to capture velocity measurements from the AGBR experimentally. If too much fluid shear and mixing is present in the AGBR system, the device is not recognized as creating low-shear modeled microgravity. According to CFD simulations, the AGBR has low shear stress. Experimental PIV results validated these simulation results. AGBR design and operational changes were evaluated to determine the effect on the shear stress within the AGBR. Optimized reactor designs are developed and manufactured for improved biological sensing and ease of use. The optimal AGBR designs are documented and ready to be used to develop biofilm control strategies for spacecraft wastewater systems.