Although current proposed water recovery systems in space do not incorporate biotreatment technologies, research has indicated that bioprocessors (BP) may be a potential primary treatment technology in integrated advanced life support systems for long-duration space missions. Little data have been reported on the activity of nonacidified wastewater in the collection system prior to entering water recovery systems. These reactions are vital in accurately quantifying biosystem performance, mass

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... lances, and microbial kinetics for bioprocessors operated on dynamic wastestreams. The bioavailable dissolved organic carbon and ammonium concentrations of storage tank grab samples may vary by up to 44 ± 9% and 81 ± 12%, respectively, in a urine-containing wastestream. A model for quantifying the average rate of microbially based holding tank activity is presented. A brief enzymatic inhibition study indicated that surfactants contained within the wastestream may be inhibiting feed tank urease activity, causing the organic carbon and ammonium variability. The aim of this research is to quantify storage tank reactions so that future bioprocessor models reflect only the activity occurring within the BP, and not that of the feed tank. Although microbially active collection vessels may be a consideration for long-duration missions, their activity should be modeled independently to avoid the "black box" approach to modeling BP dynamics. The results will aid future researchers in operating biosystems on urine-gray water wastestreams. mon biosystem feed tanks has caused high standard deviations in influent data, significantly affecting bioprocessor removal data (11, 16) . Research on this system employed grab sample techniques at various locations within the system, with the majority of the samples being taken from influent and effluent collection vessels. Some of the problems encountered included inaccurate influent ammonium (NH 4 + ) and dissolved organic carbon (DOC) concentrations. System operation alterations (such as 24-h storage of urine) were made to correct this problem, but the 24h high variability of ammonia (from 120 to 630 mg N/L) and DOC (from 105 to 805 mg DOC/L) in the feed tank persisted. Bioavailable DOC should be estimated for similar wastestreams as the urine within the EPB stream comprises an average of 75% of the DOC, with the remaining 25% being contributed by