(510r) Modeling Bioplastic Production from Astronaut Organic Wastes for Resource Recovery Using Coupled Anaerobic-Aerobic Bioreactors for Long-Duration Space Operations

The National Aeronautics and Space Administration (NASA)’s Artemis program centers on sustained lunar surface exploration and technology validation. Incorporated into the program are extended lunar missions. NASA and its partners intend to develop an initial base camp at the lunar South Pole, which includes a lunar habitation module and in-situ resource utilization systems. Over time, NASA will conceivably establish a permanent presence, which will require enhanced environmental control and life support systems. Additionally, as more astronauts populate a permanent lunar base, questions concerning increased astronaut wastes need to be answered with sustainable, cradle-to-cradle solutions that recover critical resources such as water, oxygen, and nutrients in-situ. Several biological approaches for recovering and reusing resources have been explored; however, there is no clear solution and significant research in this area is required.

This project proposes and models a cradle-to-cradle approach for converting astronaut waste streams (urine, fecal matter, and grey water) into usable products, which can be subsequently recycled in situ. Specifically, our team first modeled an anaerobic-aerobic bioreactor system to convert the chemical energy in organic wastes to methane and biodegradable bioplastics. The anaerobic portion of the modeled bioreactor system consisted of an upflow anaerobic sludge blanket (UASB) and an anaerobic membrane bioreactor (AnMBR) for conversion of organic material to methane. Second, the liquid effluent from the anaerobic bioreactor system was routed to a distillation unit for separation of potable water from a concentrated nutrient stream (consisting of residual nitrogen, phosphorous, and trace metals). Third, the methane-rich biogas produced from the anaerobic bioreactors was routed to an aerobic bioreactor for suspended growth of methanotrophic proteobacteria. Certain strains of methanotrophs (we modeled strain Methylocystis parvus OBBP) can accumulate polyhydroxybutyrate (PHB), which can be harvested and converted to a biodegradable bioplastic. Fourth, residual methanotrophic biomass was considered for use as a food stuff, while wasted anaerobic sludge was considered as a fertilizer. Once each product (bioplastic, water, fertilizer, nutrient stream) is used, each can conceivably be digested anaerobically with urine, fecal matter, and grey water, thereby creating a cradle-to-cradle system for resource recovery.

To estimate bioplastic production, our team first conducted laboratory work to validate and strengthen existing knowledge concerning the anticipated chemical constituents of astronaut wastes using ersatz formulas. Three different waste permutations were explored: (1) fecal matter only; (2) fecal matter and urine; and (3) fecal matter, urine, and grey water. Results of chemical oxygen demand (COD) and ammonia provided an estimation of the total chemical energy in each waste permutation. Published anaerobic bioreactor conversion efficiencies were used to model biogas and methane production. Further, studied values for methanotrophic yield were used to estimate biomass production (grams volatile suspended solids, VSS) and PHB yield. Monte Carlo Simulation was employed to increase confidence in biomass and PHB yield results. Initial modeling results suggest that a lunar base consisting of five astronauts may produce between 30 and 430 grams of intracellular PHB per day. Production rates for potable water, methanotrophic biomass, concentrated nutrients, waste anaerobic sludge, as well as oxygen and energy requirements, were also determined. While further refinement of our team’s modeling approach is required, initial results suggest that an anaerobic-aerobic bioreactor system creates a cradle-to-cradle approach for resource recovery and may be viable for a larger-scale lunar base.