Few data are available on biodegradation rates of materials over the long-term (more than 30 days). This information is necessary to conduct trade studies (studies used to make selections between alternatives) comparing various degrees of biodegradation versus combining biodegradation with incineration for advanced life support (ALS) systems. This paper describes the extreme case in which solids are degraded only by biodegradation.Data on biodegradation of insoluble solids from inedible parts of tomato plants are fitted to single and double exponential decay models to obtain half-life estimates for these materials. The data were obtained from batch experiments of material degradation over a 128-day period using mixed microbial cultures including activated sludge and an inoculum of Phanaerochaete Chrysosporium, a fungus known for its ability to degrade lignin.The results suggest that the plant material can be modeled as a solitary degrading material or as a mixture of fast-degrading materials and slow-degrading materials. The fast-degrading material composes about 50% of the total biomass and decays with a half-life of 22 to 33 days. The slow-degrading material composes the balance of the mass, and in some cases there is no detectable degradation.These results are used to calculate the total amount of biomass storage required for a steady-state process that would produce complete biodegradation of all insoluble, inedible plant matter. Storage requirements for complete biodegradation range from 117 to 315 kg for each kg/d organic loading, based on a one-component (solitary degrading material) model.