Anaerobic Digestion for Reduction and Stabilization of Organic Solid Wastes During Space Missions: Laboratory Studies

The technical feasibility of applying anaerobic digestion for reduction and stabilization of the organic fraction of solid wastes generated during space missions was investigated. This process has the advantages of not requiring oxygen or high temperature and pressure while producing methane, carbon dioxide, nutrients, and compost as valuable products. High-solids leachbed anaerobic digestion employed here involves a solidphase fermentation with leachate recycle between new and old reactors for inoculation, wetting, and removal of volatile organic acids during startup. After anaerobic conversion is complete, the compost bed may be used for biofiltration and plant growth medium. The nutrientrich leachate may also be used as a vehicle for nutrient recycle. Physical properties of representative waste feedstocks were determined to evaluate their space requirements and hydraulic leachability in the selected digester design. Anaerobic biochemical methane potential assays were run on several feedstocks to determine extent and rates of bioconversion. Modifications for operation of a leachbed anaerobic digestion process in space environments were incorporated into a modified design, including flooded operation to force leachate through feedstock beds and separation of biogas from leachate in a gas collection reservoir. The results of runs in a prototype laboratoryscale reactor system operated on simulated solid waste blends are presented.