| Summary: | Thermophilic aerobic digestion was investigated as a potential waste treatment technology for biodegradable wastes generated in a long-term closed eco-system. The overall objectives of this research were to contribute to a regenerable closed-loop system for food production and water, air and waste treatment, while also minimizing the mass, volume, power, cooling and labor needs of the overall system. Biological treatment becomes more feasible due to resupply constraints with longer utilization scenarios. Though designed for long-term space mission application, this research has application for waste treatment in any closed-loop ecosystem, (e.g. arctic regions, deep-sea exploration, etc.), and valuable insight was gained that will enhance knowledge on aerobic thermophilic digestion for municipal waste and wastewater treatment. Goals included volume reduction of the wastes, enhancing potential for resource recovery including carbon, water and nutrients, and pathogen inactivation. Advantages of the system include reduced retention time, increased rapid pathogen inactivation, lower reactor volume requirements, and ease of automation as compared to other biological waste treatment systems. The primary research objectives of this research included the evaluation of the system, including effects of influent solids loadings, hydraulic retention time, oxygen transfer, and operational parameters such as pH, ORP, and temperature. Solids degradation levels of 74-78% and lignin degradation rates of 81% were consistently achieved. Nitrogen dynamics during treatment were discussed, and evaluation of start-up of the system was completed including utilization of pH adjustment during the first day to shorten the time required for attaining stable cycling. Start-up parameters were evaluated in transition to stable cycling, including volatile fatty acids, alkalinity, pH, and total ammonia nitrogen. Stable cycling conditions were forced using pH adjustments, shortening the time requirement to approximately 3-4 days compared to 1 ...
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