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Our long term objective is to utilize the photocatalytic property of titanium dioxide (TiO2) to convert volatile organic compounds (VOC) in contaminated air to carbon dioxide as a measure of total organic carbon (TOC) for risk assessment in space crafts. Photocatalytically active TiO2 surfaces prepared using Degussa P25 and sol-gel methods were evaluated for this purpose. Photocatalytic oxidation (PCO) of representative air contaminants (e.g. ethanol, toluene, dichloromethane, and acetaldehyde) by Degussa P25 immobilized on aluminum substrate revealed several shortcomings that are not suitable for our intended application. A series of experiments were conducted to optimize parameters during TiO2 sol preparation and thin film deposition.

Bioregenerative processes for the replenishment of plant nutrients in CELSS are being evaluated. Continuous operation of a breadboard-scale aerobic bioreactor (breadboard-scale aerobic bioreactor, 120 L working volume) has been used successfully to resupply partially the nutrients required for hydroponically grown wheat (4 m2 growing area, 57 days bioreactor operation) and potato (8 m2 growing area, 310 days bioreactor operation). Bioreactor performance, measured by reduction in volatile solids (27 to 37% wheat, ca. 51% potato) and mineralization of biomass C (24 to 37% wheat, 35 to 61% potato), depended on process parameters such as retention time.

Ground studies are continuing at Kennedy Space Center to define the performance of the Immobilized Microbe Microgravity Water Processing System (IMMWPS), a denitrifying, fixed-bed reactor designed for shuttle flight-testing. The goal of these experiments was to define organic compounds that could be used as indicators of changes in reactor performance as to the removal of surfactant and to evaluate additional flight and sampling protocols. While changes in the breakthrough concentration of surfactant would provide insight into performance changes during the flight experiment, this breakthrough of surfactant in the flight system is undesirable due to operational problems resulting from foaming of the undegraded surfactant. By monitoring a degradation intermediate instead of the surfactant in the effluent, this problem could be avoided while monitoring any effects of microgravity on bioreactor performance during space flight.

Regenerative life support systems are under development to reduce the need for resupply of essential commodities during long duration space missions. If higher plants are used to supply food, oxygen, and potable water, composters could be used to stabilize solid wastes, provide CO2 and nutrients to the plants, and achieve pathogen reduction. Small-scale aerobic composting was used successfully to degrade organic compounds in inedible potato biomass. Soluble nutrients were extracted from the compost at concentrations that supported seed germination. Further work is indicated to understand the inhibitory effects of some leachates. Future composter designs should allow improved performance through better instrumentation and process control.

Bioprocessing of human fecal wastes may be an important means for recycling of crop nutrients within a closed Advanced Life Support System. The objectives of this study were to determine the levels of key crop nutrients that can be extracted from human feces that had been autoclave sterilized vs. those that had not. When compared with inedible ALS grown wheat residues, the contribution of feces, which has an ash content 13% to the total potential, recoverable minerals may be small. This paper discusses results from bioreactor runs obtained using continuous stirred tank reactors with an 8 day batch culture of autoclaved or not autoclaved feces. The results suggest that feces should not be autoclaved if mineral recovery is desired. Biodegradation of feces ranged from 27 to 39% in 8 days, with 67 to 79% reduction in soluble total organic carbon (TOC) and concomitant production of carbon dioxide (CO2).

Growing plants on Mars can reduce the amount of re-supply that a long term human presence will require. A plant growth structure has been designed to test plant performance in a derived Martian atmosphere. The unit will support different lighting and nutrient systems to allow for a large range of plant experiments. The plant growth structure will be tested in a Martian simulator, which is currently under construction at the Kennedy Space Center. The simulator is a commercially available Thermotron environmental testing chamber (1.22m x 1.22m x 1.52m). The Thermotron can accommodate the input of a derived. Martian atmosphere whose composition will be defined by the experimenter. Carbon dioxide, oxygen, nitrogen, and argon will be the major constituents. Testing will be done to determine the temperature, humidity, and pressure ranges that the unit can control.