John T. Holtsnider

Brine Dewatering Using Ultrasonic Nebulization

Recovery of water from brine is a critical element of water loop closure for future extended manned space missions where water resupply logistics become increasingly prohibitive beyond low earth orbit (LEO). In these situations, brines will be derived from pooled wastewater in which the primary water recovery system recovers greater than 90% of the original water while the remaining water is retained in a contaminant laden brine. In this paper, the use of ultrasonic nebulization to recover water from brine is described. This novel method utilizes ultrasonic energy to eject micron-sized droplets of brine from the air-liquid interface forming a mist that is readily dried under a partial vacuum at moderate temperature. For brine originating from urine and other metabolic byproducts, low drying temperatures prevent decomposition of thermally sensitive contaminants. Ultrasonic nebulizer advantages include mist creation without nozzles that can become plugged, minimal power requirements, and simple and compact design. Once generated, the mist is transferred to a drying chamber where rapid drying occurs at low temperature due to the small droplet size and vacuum conditions. Following capture of the dried brine aerosol by a regenerable filtration method, water vapor is condensed and recovered. Significant findings from this program presented in this paper include: 1) water recoveries of greater than 95% were demonstrated for the Ultrasonic Brine Dewatering System (UBDS); 2) mist generation depends directly on the sweep gas flow rate, which impacts dryer, filtration, and condenser designs; 3) mist and brine compositions are identical, allowing long-term nebulization without the formation of precipitates; 4) particle removal feasibility was demonstrated; 5) microgravity compatibility is feasible when an ultrasonically transparent, open wicking material is present at the liquid-gas interface, and; 6) dried brine particles retained less than 5% moisture. These findings demonstrate the potential for continued advancement of the UBDS technology.

Development and Testing of a Microwave Powered Regenerable Air Purification Technology Demonstrator

Dielectric heating via microwave irradiation of contaminant laden sorbents offers distinct advantages in comparison to conventional thermal regeneration techniques. High temperatures may be achieved very rapidly because electromagnetic energy is absorbed directly by the sorbent material. A Technology Demonstrator, incorporating efficient rectangular waveguide based sorbent cartridge designs and effective microwave transmission systems was designed, fabricated and tested. Importantly, the performance of the Molecular Sieve 13X Waveguide Cartridge for the removal of water vapor, the Molecular Sieve 5A Waveguide Cartridge for the removal of CO2, and the Activated Carbon Waveguide Cartridge for removal of volatile organics from air, were each validated by successive sorption/ microwave desorption cycles.

Airborne trace organic contaminant removal using thermally regenerable multi-media layered sorbents

A cyclic two-step process is described which forms the basis for a simple and highly efficient air purification technology. Low molecular weight organic vapors are removed from contaminated airstreams by passage through an optimized sequence of sorbent media layers. The contaminant loaded sorbents are subsequently regenerated by thermal desorption into a low volume inert gas environment. A mixture of airborne organic contaminants consisting of acetone, 2-butanone, ethyl acetate, Freon-113 and methyl chloroform has been quantitatively removed from breathing quality air using this technique. The airborne concentrations of all contaminants have been reduced from initial Spacecraft Maximum Allowable Concentration (SMAC) levels to below the analytical limits of detection. No change in sorption efficiency was observed through multiple cycles of contaminant loading and sorbent regeneration via thermal desorption.

Mesoporous Oxide Supported Catalysts for Low Temperature Oxidation of Dissolved Organics in Spacecraft Wastewater Streams

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 CO 2 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). This structure results in high surface area, high pore volume, and reduced distances for reactants and byproducts to diffuse to and from interior catalyst sites, as compared to the tortuous diffusion path in conventional, high surface area microporous (1-2 nm) supports. Mesocellular Foams (MCFs) composed of silica-zirconia solid solutions, chemically impregnated with platinum and ruthenium, were found to produce the most active catalyst. This catalyst proved capable of mineralization of acetic acid, a refractory organic, at ambient temperature.

Ambient Temperature Removal of Problematic Organic Compounds from ISS Wastewater

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. Adsorption onto activated carbon formed from pyrolyzed polymeric beads was shown to be the most practical method for acetone removal.