Search Results

The removal of volatile organic compounds (VOCs) from the air aboard spacecrafts is necessary to maintain the health of crewmembers. The use of photocatalysis has proven effective for the removal of VOCs. A majority of studies have focused on thin films, which have a low adsorption capacity for contaminants and intermediate oxidation byproducts. Thus, this study investigates the use of adsorbent materials impregnated or coated with titania to: (1) provide a system that can remove VOCs for a period of time in the absence of UV irradiation to reduce power requirements and/or offer contaminant removal in the event of lamp failure and (2) improve the photocatalytic oxidation efficiency by concentrating VOCs and intermediate oxidation byproducts near the surface of the photocatalyst. Two adsorbent materials (porous silica gel and BioNuchar120 activated carbon) and glass beads were tested as catalyst supports for the destruction of a target VOC, in this case methanol (Co = 50 ppmv).

A sub-scale testbed for characterizing the dynamic performance of regenerable adsorbents for filtering trace contaminants (TCs) from cabin atmospheres was built and tested. Regenerable adsorbents employed in pressure-swing adsorption (PSA) systems operate in a dynamic environment, where they undergo repeated loading / regeneration cycles. Adsorbents have a given chemical specificity for non-methane TCs depending on their composition, and on the humidity and temperature at which they operate. However, their ability to filter TCs is also affected by contact time, cycle time, regeneration vacuum quality and thermal conditioning.

Two widespread practices in water treatment are, removal of pollutants via adsorption onto activated carbon, and, oxidation of pollutants using a photocatalyst slurry and ultraviolet radiation. The ultimate goal of this research is to combine the adsorptive properties of carbon and the oxidative properties of titanium dioxide (TiO2), and construct a photocatalytically regenerative carbon filter for 100% water recovery. The premise is that the activated carbon, coated with TiO2, will capture the compounds through traditional filtration and adsorption. Once the carbon becomes exhausted, it can be regenerated in-situ by turning on the UV lamps thereby activating the photocatalyst.

The technical feasibility of applying anaerobic digestion for reduction and stabilization of the organic fraction of solid wastes generated during space missions was investigated. This process has the advantages of not requiring oxygen or high temperature and pressure while producing methane, carbon dioxide, nutrients, and compost as valuable products. High-solids leachbed anaerobic digestion employed here involves a solid-phase fermentation with leachate recycle between new and old reactors for inoculation, wetting, and removal of volatile organic acids during startup. After anaerobic conversion is complete, the compost bed may be used for biofiltration and plant growth medium. The nutrient-rich leachate may also be used as a vehicle for nutrient recycle. Physical properties of representative waste feedstocks were determined to evaluate their space requirements and hydraulic leachability in the selected digester design.

A magnetically agitated photocatalytic reactor (MAPR) has been developed and tested as a post-processor in the past using phenol and reactive red dye to simulate these waste components, yet these components ignore factors that may hinder a photocatalytic post processor including competitive adsorption of various organic compounds and their oxidation byproducts and the demonstrated detrimental effect of inorganic compounds such as ammonium bicarbonate on photocatalytic oxidation. To assess these effects, this work looks at photocatalytic oxidation of air evaporation subsystem (AES) ersatz water while modifying the photocatalyst mass, magnetic field current and frequency to find the optimal conditions. Additionally, the magnetic photocatalyst has been characterized to observe the assembled structures formed when exposed to the magnetic field array in the MAPR and the crystallinity of the titanium dioxide coating.

Post-treatment of anaerobically digested residue produced during long term space missions was investigated. Solid waste was anaerobically digested by employing the SEBAC system. One of the goals of post-treatment step is to convert ammonia in the residue to nitrates via biological nitrification processes. It was found that anaerobically digested residue contained nitrifying microorganisms which could be activated by aeration. Without supplying any external nitrifying inoculum, nitrification was initiated within 2 days by continuously blowing air at 15 ml/min. The maximum rate was 0.78 mg /g dry weight /day. However, denitrification process occurred soon after nitrification and ∼ 50% of nitrate was denitrified. A modified system in which aeration was carried out by holding air within the reactor at a pressure of ∼ 10 psi yielded a higher initial specific nitrification rate of 1.7 mg/g dry weight/day. Moreover, nitrification was initiated within a day.

This paper describes an opportunity for commercial application of NASA space-based technology. Specifically, it describes application of the University of Florida's patented space-based SEBAC-II solid waste management technology to the US beet sugar industry. The project is entitled “Conversion of Biomass into Energy and Compost through Sequential Batch Anaerobic Composting”, and is being funded by the Xcel Energy Renewable Development Fund. It will be carried out by a team of researchers from the University of Florida in partnership with American Crystal Sugar Company (ACSC) of Moorhead, MN, and Minnesota Technology Inc. (MTI) in Minneapolis, MN. American Crystal Sugar generates 400 tons of sugar beet tailings daily. These tailings are a waste by-product of the raw sugar beet receiving, handling and washing operations. Currently, the company pays to have this material hauled away at the rate of 16 truckloads per day.

Surface defects were demonstrated to result from high productivity machining (HPM) as well as conventional machining of a titanium alloy Ti-6Al-4V, with HPM causing the larger sized defects. These defects could act as initiation sites for fatigue cracks showing that machining would affect fatigue strength and life of the part produced. A finishing pass appears to remove the defects. Better understanding is needed of the relationships between machining, surfaces, and strength.