Solid-Phase Thermophilic Aerobic Reactor (STAR) Processing of Fecal, Food, and Plant Residues

Background The Solids Thermophilic Aerobic Reactor (STAR) was investigated for the initial treatment of all biodegradable solid wastes that would be generated in a crewed mission, including inedible plant wastes, paper, fecal matter, and food wastes. STAR operates similarly to the autothermal thermophilic aerobic digester (ATAD) currently in use in a number of wastewater treatment plants. The projected advantages of the STAR system include a reduced retention time, increased rapid pathogen inactivation, lower reactor volume requirements, and ease of automation as compared to other biological waste treatment systems. The system operates under thermophilic, microaerobic high moisture conditions. Temperatures are maintained at 55-65°C. ATAD has been shown to inactivate indicator bacteria, thermotolerant coliforms and enterococci, and Salmonella spp., and has proven capable of producing Class A biosolids suitable for agricultural land application when operated at stable and appropriate operational parameters, which mainly include temperature, mixing and retention time. The STAR system includes the EVAC toilet, which is plumbed to a storage tank where waste is transported via vacuum. The reactor is batch fed from the storage tank once per day, and consists of a stainless steel tank with a heating band, an air diaphragm pump to circulate the sludge, piping for mixing and aeration, and a scrubber system. A visual sight gauge as well as pressure sensors allow monitoring of volume, and online monitoring includes pH, ORP, CO 2 , temperature, and O 2. Operational parameters were evaluated to optimize solids degradation and resource recovery while minimizing ESM within the system. Recycling of effluent supernatant was evaluated, studying the effects of recycling of supernatant and the affiliated enzymes and thermophiles both to increase degradation and reduce the amount of water added to the influent to increase moisture levels. Lignin degradation was evaluated in STAR, as this organic component is typically the most recalcitrant. The knowledge gained in the completion of the work contained herein will benefit other downstream technologies and ALS systems, and will continue progress on the path to a regenerative long-term habitat.