Development of an Exploration-Class Cascade Distillation Subsystem: Performance Testing of the Generation 1.0 Prototype

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1 45th July 2015, Bellevue, Washington ICES Development of an Exploration-Class Cascade Distillation Subsystem: Performance Testing of the Generation 1.0 Prototype Miriam J. Sargusingh 1, and Michael R. Callahan 2 NASA Johnson Space Center, Houston, TX The ability to recover and purify water is crucial for realizing long-term human space missions. The National Aeronautics and Space Administration and Honeywell co-developed a five-stage vacuum rotary distillation water recovery system referred to as the Cascade Distillation Subsystem (CDS). Over the past three years, NASA s Advanced Exploration Systems (AES) Water Recovery Project (WRP) has been working toward the development of a flight-forward CDS design. In 2012 the original CDS prototype underwent a series of incremental upgrades and tests intended to both demonstrate the feasibility of potential onorbit testing and to collect operational and performance data to be used to inform a second generation design. The latest testing of the CDS Generation 1.0 prototype was conducted May 29 through July 2, Initial system performance was benchmarked by processing deionized water and sodium chloride solutions. Following, the system was challenged with analogue urine waste stream solutions stabilized with an Oxone-based and the International Space Station baseline and alternative pretreatment solutions. During testing, the system processed more than 160 kg of wastewater with targeted water recoveries between 75 and 85% depending on the specific waste stream tested. For all wastewater streams, contaminant removals from wastewater feed to product water distillate, were estimated at greater than 99%. The average specific energy of the system was less than 120 W-hr/kg. The following paper provides detailed information and data on the performance of the CDS as challenged per the WRP test objectives. Nomenclature AES = Advanced Exploration Systems CD = Cascade Distiller CDS = Cascade Distillation System or Cascade Distillation Subsystem CFS = Core Flight Software COTS = commercial off the shelf CTSD = Crew and Thermal Systems Division DI = deionized g = grams IC = ion chromatography ICPMS = inductively couples mass spectroscopy ISS = International Space Station JSC = Johnson Space Center k = conductivity kg = kilogram L = liters LEO = low Earth orbit LSS = Life Suport Systems psia = pounds per square inch absolute PTAU = pretreated augmented urine 1 Life Support Systems Engineer, Crew and Thermal Systems Division, 2101 NASA Parkway/EC2 2 Principal Investigator, Crew and Thermal Systems Division, 2101 NASA Parkway/EC3

2 PTU = pretreated urine TSD = total dissolved solids THP = Thermoelectric Heat Pump TIC = total inorganic carbon TN = total nitrogen TOC = total organic carbon TRL = Technology Readiness Level TS = total solids TSS = total suspended solids UPA = Urine Processor Assembly VCD = Vapor Compressor Distiller WRP = Water Recovery Project I. Introduction N 2011, the Advanced Exploration Systems (AES) Water Recovery Project (WRP) was tasked with technology I development that will make closed-loop regenerative water recovery and management systems for future human exploration missions beyond low Earth orbit (LEO) more affordable, more reliable, and that will reduce technical risks associated with technology infusion. The Cascade Distillation Subsystem (CDS) was part of the WRP technology portfolio. A result of a previous distillation down-select study, the CDS was considered the preferred technology for technology development due to its prospects for being a more reliable system with a lower equivalent system mass (ESM) as compared to the state of the art (SOA) vapor compression distillation (VCD) system currently in operation for wastewater recovery aboard the International Space Station (ISS). 1 The objective of the WRP was to push the CDS Technology Readiness Level (TRL) to level 6 such that it is ready for insertion into a flight mission architecture. Through the AES Life Support Systems (LSS) Project, Honeywell and the NASA Johnson Space Center (JSC) are continuing their collaboration effort to develop a CDS flight system that could serve as a payload demonstration on the International Space Station (ISS) as early as This report details the interim results associated with the upgrade and test of the CDS prototype, with specific focus on demonstrating the ability of the system to process relevant ISS and exploration wastewater streams. A. Cascade Distillation System The CDS uses a multistage vacuum rotary distiller to recover water from spacecraft wastewater feed streams. A simplified model of the process stream flow for the five-stage distillation engine is shown Figure 1. The system has been described in previous papers. 2-5 The key components of the CDS include the distiller, the heat pump, three tanks, the vacuum pump, a trim cooler, feed and product flow regulators and various valves to manage the flow. The system also includes a power distribution system and an embedded controller capable of automating the core batch operation of the CDS without human interaction. Additional instrumentation is needed to support this automation process. Water is recovered in the Cascade Distiller II. Background Figure 1. Simplified block diagram of a cascade distillation system. The blue stream represents the flow of distillate, the yellow stream indicates the flow of waste water, both fresh and partially concentrated, the orange stream represents concentrated brine, and the green stream represents the flow of vacuum. (CD). Influent feed and recycled brine solutions are fed into the rotating drum at various stages in the distillation process. Vapor formed in each distillation chamber is condensed on the surface of the partition opposite the next evaporation stage. Each of the five distillation compartments is maintained at a successively lower operating pressure and temperature, allowing the heat of vaporization to be recovered four times. 2

3 External to the CD, a thermoelectric heat pump (THP) is used to provide heat energy to the hot side of the liquid recirculation loop. The THP also provides cooling energy to the cold recirculation loop to remove the heat of vaporization not recuperated from the process. A trimming heat exchanger provides additional cooling energy to balance thermal inefficiencies. Operating at reduced pressure and recovering the latent heat of vaporization serve to reduce the CDS energy requirements. The centrifugal forces generated by the rotation of the CD drum provide for phase separation in a microgravity environment. In combination with the pressure management, the centrifugal forces provide the motive force by which fluids are transported throughout the system, allowing the CDS to forgo the added mass and complexity associated with using separate pumps. B. The CDS Test System A high fidelity prototype of the system, shown in Figure 2, was co-developed by Honeywell International and the NASA JSC. This system participated in a down-select test conducted by NASA in 2009 where it was compared to like spacecraft distillation technologies by an independent panel of experts. The panel concluded that the CDS showed adequate development maturity, produced the highest product water quality, and provided competitive weight and power estimates to warrant further development as a potential exploration life support technology. Several upgrades to the CDS prototype were implemented under the AES WRP. These upgrades included implementation of an all ceramic shielded packed bearing design, intended to reduce bearing corrosion observed in previous development testing. Upgrades also included incorporation of new cold loop and product tank conductivity sensors, providing more accurate and precise measurement of distillate water quality during processing. Also replaced, were the hot and cold loop flow meters Figure 2. The CDS test system in the JSC AES Water Lab. The Cascade Distillation Subsystem (CDS) is contained in the blue box on right, and is supported by the AES Facility Support System contained in the silver racks in the center and to the left. from gauge based visual rotameters to digital flow meters. The digital flow meters provide the capability for in-line data logging and a more precise measurement of loop flow that can be used to help close the thermodynamic balance of the system. Finally, improved hot and cold flow switch technology was implemented as a more accurate control measure during filling of the two loops during autonomous operation. The CDS control system was also updated with control software that could better accommodate the Core Flight Software (CFS) being developed and implemented by other AES projects. It is expected that this software will provide the platform for an exploration mission avionics systems. III. Materials and Methods A. CDS Test Operations General operation of the CDS was conducted according to procedures adapted from those provided by Honeywell at system delivery. In general, solution processing included a series of three consecutive batches for each unique test solution type. The CDS was operated in batch mode using the nominal operational settings listed in Table 1. A batch process includes system start up, waste stream processing, system shutdown and sampling. During start up, the distiller is spun to operational speed and the system is brought down to vacuum. The cold loop is filled with purified water, the hot loop is filled with the test solution and the THP is energized to transfer heat from the cold loop to the hot loop thereby initiating the distillation process. 3

4 During waste stream processing, also referred to as steady state operations, purified distillate evaporated from the hot loop is moved to the cold loop where it is condensed and removed to the product tank. Fresh influent test solution is continued to be fed to the hot loop at a rate equal to the rate of mass transfer of distillate to the cold loop. The wastewater brine containing the residual contaminants is recirculated through the hot loop becoming more and more concentrated as the batch progresses. System shutdown is initiated when the targeted batch size is achieved, as indicated by the feed tank weight. The batch size is a function of the targeted recovery rate, which is established to maintain concentrations of contaminants in the hot loop below the anticipated solubility limit for the solution under test. After system shutdown, approximately 100 ml were collected from the feed, product, and brine tanks from the sample port valve located at the base of each respective tanks. The contents from the vapor trap were also collected per batch run. After sample collection, the tanks were drained and the test system was prepared for the next batch. To minimize cross-contamination of the system between the unique test solutions, the system was cleaned by changing out the CDS hot loop filter and processing with DI water to a pre-described cleanliness level after the completion of each test series. B. Test Objectives The current phase of CDS development had two primary objectives. The first objective was to benchmark the performance of the CDS in its upgraded configuration. Solutions selected for benchmarking included feed streams that had been tested in previous CDS development work. 3 The specific benchmark solutions were DI water, 2% sodium chloride (NaCl) and a human-generated urine feed stream stabilized using an Oxone-based pretreatment formulation. The DI test solution provided a baseline for thermodynamic performance of the system when processing without introduction of a contaminant load. The sodium chloride solutions were used to demonstrate phase separation and removal by distillation of dissolved salts using solutions with solids concentrations approaching that of urine waste streams. The sodium chloride solutions were also chosen as a simple and reliably generated standard for evaluating CDS performance trends over its test life cycle. Finally, the Oxone stabilized urine provided a performance benchmark when processing a complex waste stream containing a full urine-like organic and inorganic contaminant waste load. Testing with these solutions allowed a comparison of data to previous system performance, providing at least a rudimentary check that the upgrades made to the CDS prototype were not having an acute and/or significant impact on system performance. Once the system performance was benchmarked, the second objective of the test was to collect data that could be used to evaluate CDS performance when processing two previously untested ISS analogue urine waste streams. This latter testing with the ISS feed streams was considered a critical development step toward one day demonstrating the CDS technology as a payload on the ISS. In general, each of the five benchmark and performance test solutions selected were processed in a series of three consecutive batches. A brief description of each test solution is provided in Section C, below. C. Test Solutions Benchmark test solutions included DI water, sodium chloride solution and an Oxone-based stabilized urine wastewater, referred to as Oxone pretreated urine (PTU). Deionized (DI) water, processed through an ion exchange system, was provided directly from the AES Water Lab DI water system. Solutions of sodium chloride were generated by dissolving 220 g of NaCl (Sigma Aldrich) into 11-L of facility DI water. Finally, Oxone stabilized urine was generated by collecting urine from human donors to which was added 5 grams of Oxone, 2.3 g of concentrated sulfuric acid and 250 g of DI flush water per liter of raw urine. The two ISS urine waste streams selected included a baseline formulation currently used to stabilize urine on the ISS. This formulation included the addition of 16.5 g of stabilizer solution containing chromium trioxide, concentrated sulfuric acid, and water. Use of this stabilizer allows up to 75% recovery of water from urine per the current target specification used for the ISS urine processor assembly (UPA). The other ISS analogue waste stream included an 4 Table 1. Nominal CDS performance testing set points. Parameter Distiller Speed THP Power * Temperature Hot Loop Cold Loop Trim Cooling Flow Rate Hot Loop Cold Loop Trim Cooling System Pressure Nominal Target Setting 1200 RPM 300 W 45º C 22º C 18º C 1.4 L/min 1.5 L/min 2.8 L/min psia *Setting correlates to a 4.0 kg/hr targeted processing rate.

5 alternative pretreatment formulation being developed for the ISS that will replace the sulfuric acid content in stabilizer solution with a non-sulfate containing acid. This latter alternative formulation is intended to reduce the risk of calcium sulfate precipitation in recovered urine brine process streams and will allow the stabilized urine to be processed back to the original UPA specification of 85% water recovery. The alternative ISS pretreatment formulation is expected to provide the stabilizer concentrations at levels similar to those used in the baseline ISS formulation. For both ISS urine test solutions, the human-generated urine was first augmented to more closely match the urine mineral content observed for in-flight ISS urine waste streams. The augmented solutions, once stabilized, are referred to ISS pretreated and augmented urine (ISS PTAU) and ISS alternative pretreated and augmented urine (ISS Alt- PTAU), respectively. A description of the augmented urine formulation can be found in Mitchell et. al. 6 Finally, all test solutions were filtered to 100 microns by passage through a stainless steel filter prior to processing through the CDS. D. Sample Analysis For each test series, water quality and thermodynamic performance data were collected. Data collected from inline sensors were logged by the CDS control system including system pressures, system temperatures, tank masses, THP and distiller motor power, and distillate conductivity in both the product tank and cold loop. Process stream samples (brine, product, influent, and vapor trap) were analyzed for, conductivity, refractive index, anions/cations, total organic carbon (TOC), total inorganic carbon (TIC), metals, total solids (TS), total dissolved solids (TDS), total suspended solids (TSS), and total nitrogen (TN). Standard chemical analyses were obtained according to methods described in reference 7. These analyses included, conductivity, and solids. measurements were made using an Orion 3-Star meter (P/N ) equipped with an Orion glass body combination 8102BN Ross electrode. Conductivity measurements were made using an Orion 3-Star conductivity meter (P/N ) equipped with a MD conductivity probe. Anions and Cations were measured by Ion chromatography (IC) using a Metrohm dual-piston pump (model 709) with a Metrohm conductivity detector (model 732). Metals were measured using an Agilent 7500 Series inductively coupled plasma mass spectrometer (ICPMS). TOC, TIC, and TN measurements were made using a Shimadzu TOC-V analyzer with ASI-V automatic sampler. IV. Results and Discussion AES FY14 performance testing began on May 29, 2014 and ended on July 2. Over the test phase, eighteen batch runs were performed and over 160 kg of influent test solution was processed, less DI water processed as part of test system checkout and cleaning cycles. Interim results from testing have been reported previously along with additional details on calculations of thermodynamic performance. 5 Table 2 provides a summary of selected thermodynamic performance parameters including batch size, water recovery rate, distillate production rate, and specific energy. The data represents average and standard deviations from three batch runs per test solution type. In general, the thermodynamic performance of the CDS with all test solutions was found to be acceptable, exhibiting relatively low specific powers and expected recovery rates. In addition, the CDS performance with the benchmark solutions (DI Water, 2% NaCl, and Oxone PTU) was considered consistent with past testing with like solutions. 1,4 These results suggest that the CD bearing and test system updates did not, in general, have any critical impacts on system performance. It was observed, however, intermittently during test and particularly toward the end of testing, that the system was exhibiting power signatures indicative of anomalous loading of the motor. Post-test disassembly and inspection of the distiller suggested some evidence of wear, machining and/or assembly issues associated with the metal shielding on the large evaporation-side bearing. The bearing shields themselves were implemented by Honeywell after procurement of commercial-off-the-shelf (COTS) bearing units. The use of the COTS bearing with shielding was intended to be a temporary solution to support prototype CDS testing while new design options for a second generation distiller were being investigated. Therefore, no effort to fix the prototype bearing system has been pursued. Instead for the generation 1.0 distiller, the shielded bearings have been replaced with the unshielded variety of the original COTS bearing. The data in Table 2 also suggests that the complexity of the wastewater stream drives system performance. For example, the urine test solutions exhibited the highest specific energies. This result is likely due to the presence of non-condensable gases in the urine waste streams requiring more work to be performed by the vacuum pump in order to maintain the pressure set point for the distillation process. Production rates also trended toward lower values in order of contaminant load, with DI exhibiting the highest production rate and the ISS PTAU solutions the lowest. This trend might be expected across the urine based waste stream as the PTAU test solutions were augmented to increase the contaminant load to better match the urine waste stream expected on orbit. The fact that Oxone is observed to have a production rate greater than that of 2% sodium chloride is likely due to the sodium chloride 5

6 solutions having a larger salt content in the influent feed stream. Finally, in Table 2 estimates of batch size and water recovery are provided using a mass based analysis of feed processed through the system, and feed processed relative to product produced. Targeted batch sizes and water recovery rates were 9.7 kg and 85% for all test solutions except the ISS PTAU baseline which had a targeted batch size 5.8 kg and a recovery rate of 75%. The lower targeted recovery for the ISS PTAU was selected based on a known increased risk of precipitation of calcium sulfate for this test solution as the brine is concentrated during the distillation process. Calcium sulfate precipitation is, in fact, the limiting factor for water recovery across the three urine-based test solutions and has driven the replacement of acid in the ISS baseline pretreatment to a non-sulfate containing acid. The recovery rate selected for ISS PTAU baseline test solution was actually 5% higher than the rate being used on ISS for processing the like urine waste stream using the UPA. Chemical analysis of the process streams was used to examine the risk of precipitation in the urine-based test Table 2. CDS Performance Summary Test Solution Batch Size, kg Water Recovery Est, % Production Rate, kg/hr Specific Energy, W-hr/kg DI Water 9.01 ± ± ± ± 7.9 2% NaCl (Trial, 1) 9.78 ± ± ± ± 0.9 Oxone PTU 9.81 ± ± ± ± 0.3 ISS PTAU 5.79 ± ± ± ± 6.3 ISS Alt-PTAU 9.77 ± ± ± ± 2.7 2% NaCl (Trial, 2) 9.76 ± ± ± ± 1.5 Details on calculation used for analysis can are provided in Callahan and Sargusingh 5 solutions and also to help verify the targeted recovery rates. These data are shown in Table 3. For this analysis, the recovery rates were based on the average of five separate recovery estimates made using feed and brine ratios of total dissolved solids, total solids, and Cl -, Na + and K + ion concentrations. The data is shown as the average of the five measurement made across the three batch runs performed for each test solution. Also provided is the maximum recovery achieved on any single batch run for each test series. Average and maximum batch values are also shown for estimates of the molar-based calcium and sulfate solubility product determined for each test solution. These values are then compared in Table 3 to brine-based estimates of the calcium sulfate solubility and used to suggest the potential for calcium sulfate to precipitate based on whether the solution is unsaturated, saturated or supersaturated with regard to these ions. Table 3. Chemical Based Recovery Estimates and Brine Calcium Sulfate Solubility Product Test Solution Recovery Est.* (%) Brine Solubility Product [Ca] B[SO 4] B M 2 Est. Calcium Sulfate Saturation in the Brine Ave (sd) Max Ave. Max Ave Max Oxone 84 ± Unsaturated Unsaturated ISS Baseline 74 ± Unsaturated Slightly Supersaturated ISS Alternate 85 ± Unsaturated Unsaturated *Average recovery based on brine to feed ratios for: total solids, total dissolved solids, and Cl -, K + and Na + ions. Molar based solubility product determined from the cross-product of Ca ++ and SO 4 2- concentrations in the CDS residual brine. The data suggests that on average the chemical based estimates of water recovery are in agreement with the weight based estimates presented in Table 2 and that the calcium sulfate solubility product averaged for the brine across the three runs for each test solution was not saturated, i.e., unlikely to precipitate. However, when looking at the maximum recovery, all estimates tended to be a few percent higher than the targeted recovery rate. For the Oxone PTU and ISS PTAU alternate test solutions this result had no effect on expected calcium sulfate saturation estimates. However, for 6

7 the ISS PTAU baseline, the maximum recovery achieved at 78% resulted in a brine that was estimated to be slightly supersaturated. On another test run with the ISS PTAU baseline the brine was estimated to be saturated at an estimated recovery rate of 74%. A similar result might have been expected for the Oxone test solution. The Oxone pretreatment, like the ISS baseline, achieves similar sulfate concentration in urine by way of the addition of sulfuric acid as part of the pretreatment formulation. However, because the Oxone test solutions were not augmented to simulate, at least in part, the calcium ion concentrations on orbit, the calcium sulfate solubility product is reduced at the 85% recovery rate and the brines remain under-saturated. Similarly, the ISS alternate pretreatment formulation replaces sulfuric acid with an alternative acid. This acid exchange lowers the concentration of sulfate ion in the final solution and maintains the calcium sulfate solubility product below saturation point at the 85% recovery rate. Further chemical analysis from the wastewater test series is provided in Table 4. Included are average values (n = 3) and standard deviations per test solution of the summed concentrations (g/l) measured by organic analysis, including: TOC, TIC, and TN; the summed concentrations (g/l) of ions measured by ion chromatography (IC), including: F, Cl, NO - 2 N, Br, NO 3 N, PO 3 4, SO 2 4, Li +, Na +, NH + 4 N, K +, Ca 2+, and Mg 2+ ; and the summed concentrations (g/l) of metals measured by ICPMS, including: Al, As, Ba, Cd, Cr, Cu, Fe, Pb, Hg, Mn, Ni, Se, Ag, and Zn. In general, contaminant removal from feed to product was estimated at greater than 99% for all non-di test solutions. Similarly, concomitant loading of the contaminants into the respective brine process streams is observed. As with the thermodynamic performance data, the trend toward higher concentrations of contaminants in the product water correlates with the higher complexity of the influent, i.e., from DI to NaCl to urine. For example, the distillate generated from the Oxone PTU influent had conductivities that were up to 19 times greater than that of the distillate generated from the 2% NaCl influent. Similarly, the ISS analog solutions have about twice the average distillate conductivity than Oxone PTU. These results are corroborated by data that suggests contaminant carryover is driven primarily by volatile materials such as organic acids rather than liquid entrainment or splash from the CDS hot loop to the cold loop. However, some liquid entrainment is expected especially during system startup. 8 Although the trends are not completely clear, specific inorganic ions measured at low levels in the urine distillates included chloride, sulfate, phosphate, and potassium. Metals detected in low concentrations included, chromium, iron, nickel, selenium, and zinc. In general, the ions were found in concentrations less than g/l with the highest concentrations detected for the Oxone PTU distillate for sulfate at less than g/l and chloride at less than g/l. The metals were generally found in the ISS PTAU distillates with concentrations of all detected Table 4. Summary of Contaminant Loads Parameter Influent Brine Distillate R (%)* DI Water 2% NaCl (Trial, 1) Oxone PTU ISS PTAU ISS Alt-PTAU 2% NaCl (2) ± ± ± ± ± ± ± 0.6 nm 2.08 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 16.6 nm 1.59 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± nm 4.05 ± ± ± ± ± ± ± ± ± ± ± ± ± ± > 99.9 > 99.8 > 99.9 > 99.9 > 99.9 *Contaminant removal estimate based on feed and distillate chemistry. Ions = the summed ions, as measured by IC analyses, which includes F, Cl, NO 2 - N, Br, NO 3 N, PO 4 3, SO 4 2, Li +, Na +, NH 4 + N, K +, Ca 2+, and Mg 2+. Metals = the sum of the total metals as measured by ICP-MS analysis, which includes Al, As, Ba, Cd, Cr, Cu, Fe, Pb, Hg, Mn, Ni, Se, Ag, and Zn. nm not measured

8 metals being at or below 5.0 x 10-5 g/l. However, despite the instances of low level contaminant carryover the initial testing suggest the product water quality from the CDS is acceptable for all influent waste streams. As part of this assessment of CDS performance, Table 5 provides a comparison of selected CDS parameters relative to the specifications for distillate water expected for delivery to a post-processing water system. From these data it can be observed that the CDS would be expected to meet or exceed the requirements for distillate water temperature, flow rate, conductivity,, ammonia and total organic carbon. More data will be collected to look at system trends and behaviors using more flight-like system configurations and processing algorithms. These tests will be used to help develop and design a second generation CDS. Table 5. Comparison of CDS Urine Process Test to Expected Distillate Delivery Specifications Parameter Specification Oxone ISS Baseline ISS Alt Temperature Range F ~ 72.0 ~ 72.0 ~ 72.0 Flow Rate 0 5 lb./hr Conductivity < 400 μmho/cm Ammonia 3 ppm < 0.6 < 0.6 <0.6 Total Organic Carbon 150 ppm V. Conclusion During the current phase of CDS development testing, the system operated as expected and with acceptable performance when processing the benchmark test solutions, DI Water, 2% NaCl and Oxone PTU. Preliminary comparison of the benchmark data to previous testing suggest the system upgrades made to the current CDS prototype have not shown any acute impacts to system performance. Similarly, the current round of testing has shown the CDS to be capable of processing ISS analogue waste streams and with performance values approaching those observed for the less complex baseline test solutions. This latter result is an important development step on the critical pathway toward demonstrating the CDS technology as part of an ISS payload. Testing of the CDS will continue to evaluate updated designs for THP, control system and new wastewater stabilization methods. In addition, the CDS prototype will also continue to be used as a test bed for informing the design and operation of the flight-forward Generation 2.0 CDS system currently under development. Acknowledgments The authors gratefully acknowledge the contribution and efforts of Otto Estrada, Chris Carrier, and Dean Muirhead of the JSC Engineering Technology and Science (JETS) contract group, and Jason Nelson on rotational assignment for the committed engineering, analysis, and support during CDS test operations. The authors thank Vipul Patel, Al MacKnight, and Mark Gee of Honeywell. Lui Wang of the JSC Robotics, Automation, and Simulation Division and Mark Guerra, Chris Dupont, and Catherine Czeto of Tietronix are acknowledged for their support on the 3T Control System. Finally, the authors acknowledge Walter Schieder and Sarah Shull of the AES LSS project. References 1 McQuillan, J., Pickering, K. D., Anderson, M., Carter, L., Flynn, M., Callahan, M., Vega, L., Allada, R and Yeh, J., Distillation Technology Down-selection for the Exploration Life Support (ELS) Water Recovery Systems Element, 40th, AIAA , AIAA, Reston, VA, Lubman, A., MacKnight, A., Rifert, V., and Barabash, P., Cascade Distillation Subsystem Hardware Development for Verification Testing, 37th International Conference on Environmental Controls, SAE, Callahan, M. R., Lubman, A., MacKnight, A., Thomas, E. A., and Pickering, K. D., Cascade Distillation Subsystem Development Testing, 38th, SAE, Callahan, M. R., Lubman, A., and Pickering, K. D., Cascade Distillation Subsystem Development Testing: Progress Toward a Distillation Comparison Test, 39th, SAE, Callahan, M. R., and Sargusingh, M. J., Cascade Distiller System Performance Testing Interim Results, AIAA Space 2014 Conference, AIAA , American Institute of Aeronautics and Astronautics, Reston, VA,

9 6 Mitchell, J.L., Broyan, J., Pickering, K., Adam, N., Casteel, M., Callahan, M. and Carrier, C. Ion Exchange Technology Development in Support of the Urine Processor Assembly Precipitation Prevention Project for the International Space Station. 42nd, San Diego, CA., APAH, Standard Methods for the Examination of Water and Wastewater, American Public Health Association, American Water Works Association, Water Environment Federation. On-line Edition 8 Loeffelholz, D., Baginski, B., Patel, V., MacKnight, A., Shull, S., Sargusingh, M. and Callahan, M. R., Unit Operation Performance Testing of Cascade Distillation Subsystem. 44th International Conference on Environmental Controls, Texas Tech University,