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A Microwave Enhanced Solid Waste Freeze Drying Prototype system has been developed for the treatment of solid waste materials generated during extended manned space missions. The system recovers water initially contained within wastes and stabilizes the residue with respect to microbial growth. Dry waste may then be safely stored or passed on to the next waste treatment process. Operating under vacuum, microwave power provides the energy necessary for sublimation of ice contained within the waste. This water vapor is subsequently collected as relatively pure ice on a Peltier thermoelectric condenser as it travels en route to the vacuum pump. In addition to stabilization via dehydration, microwave enhanced Freeze Drying reduces the microbial population (∼90%) in the waste.

Waste Management Systems (WMSs) designed for use aboard long-term spacecraft missions and within Lunar and planetary habitations must reduce volume and recover useful resources from solid wastes, as well as impart chemical and microbial stability to stored wastes. Many WMS processes produce high concentrations of toxic emissions that can periodically overwhelm Trace Contaminant Control Systems (TCCSs) designed to handle nominal atmospheric contaminants. A prototype Catalytic Oxidation System (COS) has been developed for this contingency, and when mated to different WMS processes, will treat these toxic emissions on an as-needed basis. The COS reactor utilizes a platinum and ruthenium bimetallic catalyst supported on mesoporous zirconia that is highly active and oxidizes at relatively low temperature a wide variety of volatile organic compounds (VOCs) and inorganic toxic emissions produced by WMS processes.

In the Sabatier reactor, oxygen is recovered (as water) by hydrogenation of carbon dioxide. One half of the reacted hydrogen is contained within the product water, the other half is used to form methane (CH4). Hydrogen resupply requirements for the oxygen recovery process can be minimized by reclamation of hydrogen from the methane waste. To this end, we have developed effective methods for the recovery of hydrogen from CH4 using a microwave plasma reactor. By selectively promoting the oligomerization reaction which forms hydrogen and acetylene, up to 75% of the waste hydrogen can be recovered in a manner which minimizes the carbon fouling and carbon build-up problems which drastically reduce the long-term viability of traditional methane pyrolysis methods using fixed bed and fluidized bed reactors.

Several solid waste management (SWM) systems currently under development for spacecraft deployment result in the production of a variety of toxic gaseous contaminants. Examples include the Plastic Melt Waste Compactor (PMWC) at NASA - Ames Research Center1, the Oxidation/Pyrolysis system at Advanced Fuel Research2, and the Microwave Powered Solid Waste Stabilization and Water Recovery (MWSWS&WR) System at UMPQUA Research Company (URC). The current International Space Station (ISS) airborne contaminant removal system, the Trace Contaminant Control Subassembly (TCCS), is designed to efficiently process nominal airborne contaminants in spacecraft cabin air. However, the TCCS has no capability to periodically process the highly concentrated toxic vapors of variable composition, which are generated during solid waste processing, without significant modifications.

A Microwave Powered Solid Waste Stabilization and Water Recovery Prototype system has been developed for the treatment of solid waste materials generated during extended manned space missions. The system recovers water initially contained within wastes and stabilizes the residue with respect to microbial growth. Dry waste may then be safely stored or passed on to the next waste treatment process. Using microwave power, water present in the solid waste is selectively and rapidly heated. Liquid phase water flashes to steam and superheats. Hot water and steam formed in the interior of waste particles create an environment that is lethal to bacteria, yeasts, molds, and viruses. Steam contacts exposed surfaces and provides an effective thermal kill of microbes, in a manner similar to that of an autoclave. Volatilized water vapor is recovered by condensation.

Gradient magnetically assisted fluidized bed (G-MAFB) methods are under development for the decomposition of solid waste materials in microgravity and hypogravity environments. The G-MAFB has been demonstrated in both laboratory and microgravity flight experiments. In this paper we summarize the results of gasification reactions conducted under a variety of conditions, including: combustion, pyrolysis (thermal decomposition), and steam reforming with and without oxygen addition. Wheat straw, representing a typical inedible plant biomass fraction, was chosen for this study because it is significantly more difficult to gasify than many other typical forms of solid waste such as food scraps, feces, and paper. In these experiments, major gasification products were quantified, including: ash, char, tar, carbon monoxide, carbon dioxide, methane, oxygen, and hydrogen.

Solid wastes can be separated from aqueous streams and concentrated by filtration in a magnetically assisted fluidized bed. In this work the filtration of solid waste materials using filter beds consisting of granular ferromagnetic media is demonstrated. The degree of bed consolidation (or conversely fluidization) is controlled by the application of magnetic forces. In the Magnetically Assisted Gasification (MAG) process, solids are first entrapped by filtration, and then fluidized and transferred to a high temperature reactor where they are thermally decomposed. The maximum particle loading for the filter bed is determined by the intergranular void space. Using magnetic methods, it is possible to manipulate the degree of compaction as the filtration progresses to increase the void space and thereby maximize the loading capacity and efficiency of the filter. This process is completely compatible with operation in microgravity and hypogravity.

In the Sabatier reactor, oxygen is recovered (as water) by hydrogenation of carbon dioxide. Half of the reacted hydrogen is contained within the product water, the other half forms methane (CH4). To close the hydrogen loop, we are investigating methods for the efficient recovery of hydrogen from CH4. This paper describes microwave plasma-based methods for the thermal decomposition (cracking) of methane to produce hydrogen, elemental carbon, and related carbonaceous substances. Two primary reactor configurations have been employed in this work: 1) a quartz tube vertically oriented within a section of rectangular waveguide, and 2) waveguide transmission through a quartz window into a cylindrical vacuum chamber based multimode cavity. Hydrogen recoveries of up to 98% have been obtained. Three primary mechanisms of methane decomposition have been identified: methane pyrolysis, methane oligomerization, and methane aromatization.