Design and Initial Tests of a Denitrification Composter to Stabilize Space-Mission Trash

The purpose of this research is to determine the feasibility of a unique denitrifying composter to stabilize trash from space-habitation (STS, ISS, ALS) life support activities. Design criteria were derived from variables to be manipulated and those to be held constant. A pre-existing aerobic composter was used and engineering tests run to ensure that requirements were met. Key experimental variables were identified: NO₃^- concentration and rate of addition, O₂ concentration, mixing duration and frequency, and inoculum. Independent variables were pH, temperature, moisture, C:N ratio, feed material, size reduction, feed addition rate, and mode of operation. Important performance parameters included: maximization of desired outcomes – BOD₅ removal, CO₂ production, waste stabilization, and denitrification – and minimization of undesired products – N₂O, NH₃, and volatile organic compounds. Baseline composter operation was with a known solid waste feed: one run was aerobic and two with denitrifying conditions. Inocula were soil or a mixed microbial community enriched under denitrifying conditions. The results indicated the absence of an adequate inoculum.