A closed-loop in situ biomanufacturing approach for bioplastic production using coupled anaerobic-aerobic bioreactor technologies during deep-space operations

As space agencies pursue deep space exploration and plan for extraterrestrial bases, logistical re-supply remains a significant barrier. The exploration of closed loop systems that recover resources for reuse from “waste” products will likely be an integral part of any future base, as will in situ manufacturing of products. This study proposes and models a bioreactor system that converts astronaut organic waste – feces and food scraps – to raw polyhydroxybutyrate (PHB) for onsite bioplastic product manufacturing. The system consists of four main steps. First, a two-step anaerobic bioreactor system (anaerobic digestion coupled with anaerobic membrane bioreactors) produces methane from organics (Step 1). Methane is then provided to methanotrophic bacteria for aerobic biomass growth and intracellular PHB accumulation under controlled stress conditions (Step 2). PHB is extracted in Step 3. Potable water and nutrients (e.g., nitrogen and phosphorous) are recovered in Step 4. Using the mass of organic waste produced by one astronaut per day as the functional unit, uncertainty modeling (Monte Carlo simulation) indicates that 4.9 ± 1.1 g of methane can be produced daily from the anaerobic portion of the bioreactor system. Once fed to the aerobic bioreactor as substrate, methanotrophic bacteria produce 3.5 ± 1.5 g of PHB daily (post extraction). Flush water and nutrients introduced into the system are sufficient for biochemical reactor system operation and biomass growth. This result suggests that PHB bioplastic via the closed loop bioreactor system may be a viable substrate for rapid on-demand fabrication of replacement parts for bases with larger astronaut populations. However, there are several technical barriers, which are discussed in this work, that need to be addressed prior to real-world employment.