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The sorption and ion exchange water reclamation technologies used to treat the waste streams in the Environmental Control and Life Support System (ECLSS) and Process Materials Management System (PMMS) are ineffective for removal of low molecular weight, polar organic contaminants which do not have ionized forms. These include likely waste stream constituents such as methanol, ethanol, isopropanol, and acetone. Catalytic oxidation of these compounds in oxygen saturated water at moderate temperatures (125 to 160 C) provides a reliable, simple, and inexpensive way to eliminate these contaminants. By the suitable choice of catalysts, these species can be converted to carbon dioxide and water or to species which can be removed effectively by sorbents and ion exchange resins. The operation requirements of the baseline system are oxygen and heat. Since much of the heat is recovered, the energy use of the technology is very low.

The inedible portion of plant biomass in closed regenerative life support systems must be reprocessed producing recyclable by-products such as carbon dioxide, sugars, and other useful organic species. High solids biomass slurries containing up to 27 wt% were successfully prepared in a stirred batch reactor and then pumped using a single piston valveless pump. Wheat straw, potato, and tomato crop residues were acid hydrolyzed using 1.2 wt% sulfuric acid at 180°C and 1.2 MPa for 0.75-1.5 hours. Viscosity for a 25 wt% acid hydrolyzed wheat straw emulsion (Bingham-plastic) was 6.5 centipoise at 3 cm/sec and 25°C.

A new technology for controlling the partial pressure of CO2 (pCO2) in a plant growth chamber (PGC) has been demonstrated. CO2 is gathered from the source atmosphere across a membrane gas exchanger and stored in an alkanolamine solution. The CO2 loading of the alkanolamine reservoir is monitored using specific conductance and controlled by the exposure time and temperature. The PGC pCO2 is maintained using a second membrane exchanger through which the alkanolamine circulates, absorbing or releasing CO2 to maintain equilibrium. The equilibrium pCO2 is determined by the CO2 loading and the temperature. Constant PGC feed pCO2 levels of roughly 1000 ppm have been maintained using sources with pCO2 both above and below this value.

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.

Small, highly polar organics such as urea, alcohols, acetone, and glycols are not easily removed by the International Space Station's Water Recovery System. The current design utilizes the Volatile Removal Assembly (VRA) which operates at 125°C to catalytically oxidize these contaminants. Since decomposition of these organics under milder conditions would be beneficial, several ambient temperature biocatalytic and catalytic processes were evaluated in our laboratory. Enzymatic oxidation and ambient temperature heterogeneous catalytic oxidation of these contaminants were explored. Oxidation of alcohols proceeded rapidly using alcohol oxidase; however, effective enzymes to degrade other contaminants except urea were not found. Importantly, both alcohols and glycols were efficiently oxidized at ambient temperature using a highly active, bimetallic noble metal catalyst.

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.

In order to meet NASA potable water standards using biological processing, additional purification is needed. Elimination of ammonia species is a significant post-treatment step to achieve this goal. New technology, combining membrane transport and electro-oxidation of ammonia, was developed to solve this problem without the use of expendables. The Aqueous Phase Ammonia Removal and Destruction System (APARDS) Phase I Program rigorously demonstrated the feasibility of each sub-process, and an integrated system was developed that removed and destroyed ammonia from a simulated bioreactor effluent. Membranes and process conditions suitable for ammonia removal have been determined. An Ammonia Removal Module (ARM) was designed for the efficient transfer of ammonia to a secondary electro-oxidation stream where the ammonia was destroyed. The electrolysis cell's electrodes, operational voltage, and flow characteristics were optimized to rapidly destroy ammonia.

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.

The investigation and development of a chemiluminescence based ethanol detection concept into a biosensor system is described. The biosensor uses alcohol oxidase to catalyze the reaction of short chain primary alcohols with elemental oxygen to produce hydrogen peroxide and the corresponding aldehyde. The reaction of hydrogen peroxide with an organic luminophore in the presence of a sufficient electric field results in emission of blue light with peak intensity at 425nm. The chemiluminescent light intensity is directly proportional to the alcohol concentration of the sample. The aqueous phase chemistry required for sensor operation is implemented using solid phase modules which adjust the pH of the influent stream, catalyze the oxidation of alcohol, provide the controlled addition of the luminophore to the flowing aqueous stream, and minimize the requirement for expendables. Precise control of the pH has proven essential for the long-term sustained release of the luminophore.

The initial development effort is described for an electrochemical hydrogen peroxide generator and pervaporation module capable of producing and delivering hydrogen peroxide to a contaminated waste water stream as an oxidant or to a pure water stream for use as a disinfectant. A three chambered cell is used to generate hydrogen peroxide by a combined electrodialysis and electrochemical process. Each chamber is separated from its neighbor by a membrane allowing selective production of peroxide anions and hydrogen ions under controlled pH conditions followed by migration to form hydrogen peroxide. Concentrations greater than 6,500mg/L have been produced in this manner. The effects of voltage, pH, membranes, electrode materials, and method of oxygen introduction are delineated. Hydrogen peroxide is then transferred to the end-use stream by pervaporation. The impact of pH, relative flow rates, and ionic strength of sink and source solutions on pervaporation rates is detailed.

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.

Novel mesoporous bimetallic oxidation catalysts are described, which are currently under development for the deep oxidation (mineralization) of aqueous organic contaminants in wastewater produced on-board manned spacecraft, and lunar and planetary habitats. The goal of the ongoing development program is to produce catalysts capable of organic contaminant mineralization near ambient temperature. Such a development will significantly reduce Equivalent System Mass (ESM) for the ISS Water Processor Assembly (WPA), which must operate at 135°C to convert organic carbon to CO2 and carboxylic acids. Improvements in catalyst performance were achieved due to the unique structural characteristics of mesoporous materials, which include a three-dimensional network of partially ordered interconnected mesopores (5-25 nm).

A variety of techniques, including supercritical water oxidation, fluidized bed combustion, and microwave incineration have been applied to the destruction of solid wastes produced in regenerative life support systems supporting long duration manned missions. Among potential problems which still deserve attention are the need for operation in a variety of gravitational environments, and the requirement for improved methods of presenting concentrated solids to the reactor. Significant improvements in these areas are made possible through employment of the magnetically assisted gasification process. In this paper, magnetic methods are described for manipulating the degree of consolidation or fluidization of granular ferromagnetic media, for application in a gravity independent three step solid waste destruction process.