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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES Appendix A Water Reclamation Systems on Mir And the International Space Station THE descriptions of the Mir water systems in this appendix reflect the systems and technology that existed and served as the basis for U.S. experiments during the U.S.–Russian Mir Phase-1A program and the technology that the Russians will transfer to the Mir segment of the International Space Station. MIRWATER-RECOVERY SYSTEMS The Mir system for water reclamation and management consists of three isolated loops: one for recovering water from urine, one for recovering potable water from the humidity condensate in cabin air, and one for recovering water from hygiene wastewater. The hygiene loop is not currently in operation and no wash water is recovered. All loops receive supplemental water supplied from Earth, which is transferred manually to each as needed to compensate for losses (Pierre et al. 1999). The urine and wash water recovery loops are located in the Kvant-2 module, and the humidity condensate purification processor is located in the Mir core module. In the first loop, water recovered from urine is used in the water electrolysis system to generate oxygen; this
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES water theoretically can be processed further to produce potable water if needed. In the second loop, humidity condensate is used to produce potable water, and it supplies about 80% of the crew's drinking water. The other 20% comes from a water resupply, which contains water produced by fuel cells aboard the space shuttle or water delivered on the Russian water tanks, called Rodnik tanks (210 liter (L) capacity), by the Russian Progress resupply vehicle. Having the make-up water supply available has allowed metabolic water balance to be maintained at all times. Each of the Russian systems currently operating in Mir is described below. Humidity Condensate Processing Most of the potable water consumed aboard Mir comes from recycled humidity condensate. This system operated successfully aboard the Salyut stations beginning in 1975, and an upgraded version operates on Mir. In the Mir system, atmospheric humidity condensate is collected and processed into potable water by a condensate water processor located in the core module. Gas and impurities are separated from the liquid (condensates), minerals and disinfectants are added, and the resultant potable water is supplied as hot or cold water for the crew. The condensate processor unit consists of four treatment subunits: a gas-liquid separator, a multifiltration bed, a conditioning-biocide addition unit, and a distribution and pasteurization system (Figure A-1). The air-condensate mixture is first passed through a 10-micrometer (µm) filter to remove particulates, and then the gas and liquid are separated by static metal plates that have hydrophilic capillary pores along the wall of the separator. The separated liquid is drawn through the pores by a negative pressure diaphragm pump, and the air is vented to the cabin. Condensate is collected in 180 milliliter (mL) aliquots and pumped to the multifiltration bed. The multifiltration bed contains ion exchange resins, activated charcoal, and a propriety room-temperature catalyst that remove inorganic and organic contaminants by cationic exchange and oxidation. The catalyst allows removal of low-molecular-weight alcohols, such as ethanol and methanol. An on-line conductivity sensor located down-
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES FIGURE A-1 The Mir humidity condensate water-reclamation system, which is planned for the early phases of the International Space Station. On the ISS, this system will be located in the service module of the Russian segment. Source: Modified from Pierre et al. (1996). stream of the multifiltration bed is used to determine whether the water is of acceptable quality (<150 microsiemens per centimeter [µS/cm]). A series of valves directs acceptable water to the conditioning bed, and unacceptable water is sent to a storage tank for recycling. Water that is accepted by the on-line sensor is processed through the conditioning bed, which adds magnesium, calcium, and other minerals to enhance palatability. Biocidal silver (0.05-0.20 milligrams per liter [mg/L]) also is added here for microbial control. Conditioned water is heated (pasteurized) to 85°C by a heat pump (regenerative heat exchanger) and stored in a heated accumulator. Hot water is available to the crew directly from the accumulator; cold water is provided by rerouting the hot water through the regenerative heat exchanger (Samsonov 1996a).
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES Filter-Reactor Catalytic Oxidation The system for water recovery from humidity condensate has been upgraded for the International Space Station (ISS) and includes an assembly that will remove organic contaminants by catalytic oxidation in an air-liquid flow at ambient temperature and pressure upstream of the multifiltration bed. This should at least double the life of the multifiltration beds (Samsonov et al. 1997). The composition of the catalyst and the process is proprietary. In fact, this “filter reactor, ” an ambient-temperature catalytic reactor, has been in operation aboard Mir since January 1998. In the service module design for the ISS, the system will have a condensate feed unit that will facilitate transfer of condensates collected from ISS modules (and stored in contingency water container bags) to the Russian condensate processor for water recovery. Urine Processing A Russian system for reclaiming water from urine has been in operation aboard Mir since January 1990. This system was designed primarily for regenerating cabin oxygen through electrolysis. The urine-processing system consists of three parts: urine preparation (collection, preservation-pretreatment, storage), atmospheric distillation, and distillate treatment and purification. These subsystems are described briefly below. The Mir urine preparation subsystem consists of the urinal, a urine-pretreatment assembly, and a blower. Urine is distilled at atmospheric pressure in a distillation unit that consists of an evaporator, condenser, heater, and brine tank. The distillate post-treatment and purification unit is identical to the humidity condensate processor. The urine is treated with sulfuric acid and a liquid solution of a commercially available oxidizer (similar to Oxone, described below), and the treated urine undergoes membrane distillation at atmospheric pressure and at relatively low temperatures. An electric heater raises the temperature to 50-52°C, and water is evaporated with a stream of air that blows at 100 L/min through the evaporator, which consists of a stack of hydrophilic capillary-porous polymeric membranes. The water vapor is condensed in a heat exchanger, cooled by an onboard coolant, and the condensed
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES liquid is processed (post-treated), as described for condensate, except for the water conditioning unit. Urine has never been used to provide potable water on Mir missions. In the life support module (LSM) of the ISS, an upgraded Russian system for processing hygiene water and urine is targeted for deployment in 2002. To meet the needs to increase processing capacity and life span of the ISS configuration and conserve energy, the Mir system will be updated for the ISS. The distillation step will receive the most re-engineering. Vacuum distillation with a rotary evaporator-condenser and a thermoelectric heat pump will be the principal component of this new system (Samsonov et al. 1996a,b). Apart from water for electrolysis, a subsystem (the water-recovery system-urine subsystem) will be added for conditioning, distributing, and preheating of the water to process it to potable quality if needed (Samsonov et al. 1997). U.S. WATER-PROCESSING SYSTEM The U.S. water-reclamation system is a single-loop system to produce potable water from a mixture of urine distillate, humidity condensate, and hygiene (wash) water, consisting of body and hand-washing water. (Laundry was deleted in the transition between the space station Freedom and the ISS program; similarly, a shower stall also has been eliminated even though the water-processing system will be designed to process water for personal hygiene.) Particulate filtration, adsorption, ion exchange, catalytic oxidation, and biocide addition are done in various subsystems. The U.S. water-processing system hardware for the ISS has been tested over the past several years in isolated and integrated modes at NASA's Marshall Space Flight Center. This test bed, the Water Recovery Test, has greatly facilitated ground-based evaluation of individual systems, components, and processes of water reclamation. The proposed U.S. integrated water-reclamation system is illustrated in Figure A-2; details of its subsystems are provided below. Urine Processing Urine and urinal flush water are collected, treated, and distilled by vapor compression before this mixture enters the water-processing sys-
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES FIGURE A-2 U.S. water-reclamation system for the ISS. MCV, microbial check valve; TOC, total organic carbon. Source: Verostko et al. (1997).
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES tem (Figure A-2). The collected urine and flush water first are stabilized to control microbes and fix ammoniated species in solution by the addition of Oxone (a proprietary potassium monopersulfate compound) and sulfuric acid. The urine and flush water are sent on for vapor compression distillation (VCD). VCD was chosen over other technologies for ISS after ground-based tests revealed that the VCD apparatus weighed less, required less power and less filtration, and produced better quality water than did other equipment. In VCD treatment, the stabilized urine is evaporated at low pressure to form water vapor, which is sent to a compressor that increases condensation temperature and pressure. The compressed vapor is directed to the condenser. The latent heat produced by condensation is transferred to provide heat for evaporation. The process of evaporation, compression, and condensation takes place between 32°C and 38°C. The resultant brine is recirculated through a recycle loop to maximize the amount of water that can be extracted. Concentrate from the system is collected in a tank within the VCD unit. If the conductivity of the distillate (measured by a conductivity sensor in the VCD unit) exceeds 120 µS/cm, it is reprocessed; if the conductivity is acceptable, the effluent is sent via a wastewater distribution line to the combined wastewater processor upstream of a particulate filter. Combined Urine and Wastewater Processing The major portion of the U.S. water reclamation system processes product water from the VCD unit (urine distillate), humidity condensate (which includes condensate from human metabolism and from off-gassing), and wash water (from the shower, hand wash, and oral hygiene). These influents are stored in a stainless steel tank and delivered to the processing system under pressure (8 pounds per square inch gauge) from a feed pump. The back pressure created on the waste distribution line by the storage unit facilitates the removal of gas, which is released into the cabin. Wastewater is passed through a 0.5-µm filter to remove particulate contaminants, and then continues to the multifiltration subsystem and on to the volatile removal assembly, as shown in Figure A-3.
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES FIGURE A-3 ISS Integrated U.S. potable-water processing system. HX, heat exchanger; MCV, microbial check valve; PCWQM, process-control water quality monitor. Source: Holder et al. (1995). Multifiltration Subsystem The multifiltration subsystem consists of two Unibed filtration units plumbed in series. Each contains various adsorbents and ion exchange
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES resins chosen for their ability to remove specific organic and inorganic contaminants expected to be present in the wastewater. The media in these units include iodinated anion exchange resin, strong and weak cation and anion exchange resins, activated carbon from coconut shell and coal, and polymeric adsorbent. Conductivity sensors are located at the multifiltration inlet, between the two Unibeds, and at the multifiltration outlet. These sensors are used to monitor Unibed performance so the units can be replaced as necessary. The Unibeds cannot remove low-molecular-weight or polar organic compounds, such as ethanol or urea. Thus, the effluent is sent to the volatile removal assembly (VRA) for further treatment. Volatile Removal Assembly The VRA consists of regenerative heat exchangers, an oxygen sparger, a catalytic reactor, a gas-liquid separator, and a “polishing” ion exchange bed (Figure A-3). The VRA oxidizes organic compounds from the multifiltration effluent to carbon dioxide. This oxidation takes place at moderate temperature. The feed water is heated twice, once as it flows through a regenerative heat exchanger and again by an immersion-type heater, and it reaches about 130°C before it enters the catalytic reactor. The oxidizing conditions and the moderate temperature help to maintain microbial contamination at less than 100 colony-forming units per 100 mL of water. After catalytic oxidation, the feed water passes back through the regenerative heat exchanger for heat reclamation before passing through a polishing ion exchange resin, which removes organic acids and other ionic contaminants. A microbial check valve adds 2-4 mg/L of iodine (and 1 mg/L of iodide) to the effluent water as a residual disinfectant. The membrane-based gas-liquid phase separator helps remove excess gas (oxygen) and other gaseous oxidation by-products from the partially cooled effluent from the reactor. REQUIREMENTS, PROPOSED LIMITS, AND MONITORING Table A-1, Table A-2, and Table A-3 present NASA's potable-water quality requirements for the ISS (Table A-1), compare NASA and Russian pro-
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES TABLE A-1 NASA Potable-Water Quality Requirements (Maximum Contaminant Levels) for the International Space Station Parameter (units) Levels Physical Parameters Total solids (mg/L) 100 Color, true (Pt-Co units) 15 Taste (TTN) 3 Odor (TON) 3 Particulates (maximum size: µm) 40 pH 6.0-8.5 Turbidity (NTU) 1 Dissolved gas (free at 37°C) NDa Free gases (at STP) NDa Inorganic Constituents, mg/Lb,c Ammonia 0.5 Arsenic 0.01 Barium 1.0 Cadmium 0.005 Calcium 30 Chlorine (total, includes chloride) 200 Chromium 0.05 Copper 1.0 Iodine (total, includes organic iodine and iodide) 15 Iron 0.3 Lead 0.05 Magnesium 50 Manganese 0.05 Mercury 0.002 Nickel 0.05 Nitrate (NO3-N) 10 Potassium 340 Selenium 0.01 Silver 0.05 Sulfate 250 Sulfide 0.05 Zinc 5.0 Bactericide, mg/L Residual iodine (minimum) 1.0 Residual iodine (maximum) 4.0 Aesthetics, mg/L Cations 30 Anions 30 CO2 15 Microbial Total count, CFU/100 mL (bacteriae/fungif) 100d Total coliformg NDd
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES Virus NDh Radioactive Constituents (pCi/L)i Organic Parameters (µg/L)b Total acids 500 Cyanide 200 Halogenated hydrocarbons 10 Total phenols 1 Total alcohols 500 Total organic carbon (TOC) 500 Uncharacterized TOCj 100 Organic Constituents (mg/L)b,c a ND, no detectable gas using volumetric gas versus fluid measurement system. Excludes CO2 used for aesthetic purposes. b Each parameter or constituent must be considered individually and independently of others. c In the event a quality parameter not listed in this table is projected, or found, to be present in the reclaimed water, the water quality manager at Johnson Space Center will be contacted for a determination of the MCL for that parameter. d Membrane filtration method. e Incubation time: 48 hr; temp.: 30 °C; medium: R2A. f Incubation time: 48 hr; temp.: 30 °C; Medium: DG-18. g ND, not detectable. Incubation time: 24 hr; Temp.: 35°C; Medium: M-Endo. h Tissue culture assay. i The MCLs for radioactive constituents in potable and personal hygiene water are to conform to Nuclear Regulatory Commission regulations (10 CFR 20). The MCLs are listed in the Federal Register, Vol 51, No. 6, 1986, Appendix B, as Table 2 (Reference Level Concentrations), Column 2 (Water). Control, containment, and monitoring of radioactive constituents used are the responsibility of the user. Before the introduction of any radioactive constituents approval is to be obtained from the Radiation Constraints Panel, which will approve or disapprove proposed monitoring and decontamination procedures on a case-by-case basis. j Uncharacterized TOC equals TOC minus the sum of analyzed organic constituents expressed in equivalent TOC. CFU, colony forming units; NTU, nephelometric (turbidity) units;Pt-Co, platinum-cobalt scale; STP, standard temperature and pressure;TTN, threshold taste number; TON, threshold odor. Source: Adapted from SSP 50005 Rev B (1995). NASA Space Station Program.This information appears in a table listed as Figure 18.104.22.168.2-1. posed contaminant limits for potable water aboard the ISS (Table A-2), and outline the schedule requirements for monitoring water quality (Table A-3).
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES TABLE A-2 Comparison of Proposed Limits for Potable Water Aboard the ISS Maximum Contaminant Levels Parameter NASA Russian Space Agency pHa 5.5-9.0 5.5-9.0 Colora 15 Pt-Co units 20 degrees Tasteb 3 TTN 2 points Odorb 3 TON 2 points Total dissolved solidsc 100, 1000 mg/L 100, 1000 mg/L Turbidityb 1 NTU 1.5 mg/L Total gas 5% volume at ATM, 20°C 5% volume at ATM, 20°C Ammonia (NH4-N) 1.5 mg/L 2 mg/L Arsenic 0.01 mg/L 0.01 mg/L Barium 1 mg/L 1 mg/L Cadmium 0.005 mg/L 0.005 mg/L Calcium 30 mg/L 100 mg/L Chlorine, total (includes Cl−) 200 mg/L 250 mg/L Chromium 0.1 mg/L 0.1 mg/L Copper 1 mg/L 1 mg/L Fluorine 1.5 mg/L 1.5 mg/L Iodine, total (includes I−) 15 mg/L 0.05 mg/L Iodine, residuald 1.0-4.0 mg/L NA Iron 0.3 mg/L 0.3 mg/L Lead 0.05 mg/L 0.05 mg/L Magnesium 50 mg/L 50 mg/L Manganese 0.05 mg/L 0.05 mg/L Mercury 0.002 mg/L 0.002 mg/L Nickel 0.1 mg/L 0.1 mg/L Nitrate (NO3-N) 10 mg/L 10 mg/L Selenium 0.01 mg/L 0.01 mg/L Silver 0.5 mg/L 0.5 mg/L Sulfate 250 mg/L 250 mg/L Zinc 5 mg/L 5 mg/L Total hardness (Ca, Mg) 7 meq/L 7 meq/L Cyanide 200 µg/L 200 µg/L Total phenols 1 µg/L 1 µg/L Ethylene glycol 12 mg/L 12 mg/L Total organic carbon (TOC) 500 µg/L 20,000 µg/Le Uncharacterized TOC 100 µg/L No limit Oxygen consumption - COD No limit 100 mg Total bacteriab 100 CFU/100 mL 10,000 CFU/100 mL Coliform bacteria <1 CFU/100 mL <1 CFU/100 mL Virus <1 PFU/100 mL <1 PFU/100 mL Agreements reached at the Joint Working Group meeting (Feb. 9-13,1998) for the shuttle-Mir and ISS water supply and water quality. a pH range applies only before iodination.
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES b Different values for U.S. and Russian-supplied water. To be further reviewed. c The 100 mg/L limit applies to the water before mineralization; thereafter, total dissolved solids may not exceed 1000 mg/L. d Range is applicable if iodine is the biocidal agent. (Silver is used as the biocide in the Russian program.) e This limit does not include the mineral counter-ion, formate. ATM, atmosphere; CFU, colony-forming units; COD, coefficient oxygen delivery; meq/L, milliequivalent per liter; NA, not applicable; NTU, nephelometric (turbidity) units; PFU, plaque-forming units; Pt-Co, platinum-cobalt scale; TTN, threshold taste number; TON, threshold odor.
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES TABLE A-3 Schedule Requirements for Water Quality Monitoring On-linea Off-lineb Measurement Potable Potable Hygiene Physical Total solids − − − Color − + + Conductivity × × × Taste and odor − + + Particulates − + + pH × × × Temperature × Turbidity − + + Dissolved gas − + Free gas − + Inorganic Compounds Ammmonia − + + Iodine × × × Specific contributorsc − + + Aesthetic Specific contributorsd − + + Microbial Total count (bacteria, fungi) − × × Total coliform − × × Virus − − − Microbe IDe − × × Radionuclidef Organics TOC ×g × × Specific organicsc − + + ×, monitoring required; −, monitoring not required; +, monitoring requirement will be waivedif verification testing and analysis indicate that the quality measurelimit will be met reliably. a Process-stream samples will be analyzed to provide real-time or near-real-time results for process control and for presumptive water quality assessment. Requirements for on-line monitoring of additional parameters will be established if verification testing and analysis indicates that such monitoring is required for process control or water quality assessment. b In addition to the on-line and off-line analyses, grab samples from the water systems will be obtained for later ground analysis. c Specification of organic and inorganic elements and compounds to be monitored will be based on the potential for those elements and compounds to be present in the product water and on their toxicity. If a parameter not listed in this table is projected or found to be present in the reclaimed water, the water quality manager at the Johnson Space Center will be contacted to determine monitoring requirements. d Selection will be based on determination of critical aesthetic parameters. e Does not include identification of viruses.
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES f The ability to monitor radionuclides during flight will be provided as part of the experiment or procedure that involves their use. g Analytical procedure could provide an indirect equivalent of classical TOC. Source: SSP 50005 Rev B, August 1995, Figure 22.214.171.124.2.1-1; InternationalSpace Station Flight Crew Integration Standard NASA STD 3000T.
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES REFERENCES Holder, D.W., D.L. Carter, and C.F. Hutchens. 1995. Phase III Integrated Water Recovery Testing at MSFC: International Space Station Configuration Test Results and Lessons Learned. SAE Technical Paper Series no. 951586, 25th International Conference on Environmental Systems, San Diego, CA, July. Pierre, L.M., J.R. Schultz, S.M. Johnson, R.L. Sauer, Y.E. Sinyak, V.M. Skuratov, and N.N. Protasov. 1996. Collection and Chemical Analysis of Reclaimed Water and Condensate from Mir Space Station. SAE Technical Paper Series no. 961569, 26th International Conference on Environmental Systems, Monterey, CA, July 8-11. Pierre, L.M., J.R. Schultz, R.L. Sauer, Y.E. Sinyak, V.M. Skuratov, N.N. Pratasov, and L.S. Bobe. 1999. Chemical Analysis of Potable Water and Humidity Condensate: Phase One Final Results and Lessons Learned. SAE Technical Paper Series no. 1999-01-2028. 29th International Conference on Environmental Systems, Denver, CO, July 12-15. Samsonov, N.M., L.S. Bobe, V.M. Novikov, N.S. Farafonov, G.K. Abramov, B.Y. Pinsky, E.I. Grigorov, E.N. Zaitsev, N.N. Protasov, V.V. Komolov, A.I. Grigoriev, and Y.E. Sinyak. 1996a. Water Supply Based on Water Reclamation from Humidity Condensate and Urine on a Space Station. SAE Technical Paper Series no. 961408, 26th International Conference on Environmental Systems, Monterey, CA, July 8-11. Samsonov, N.M., L.S. Bobe, V.M. Novikov, B.Y. Pinsky, N.V. Rykhlov, V.A. Soloukhin, N.S. Farafonov, N.N. Protasov, V.V. Komolov, V.G. Rifert, and V.V. Rakov. 1996b. Problems of Developing Systems for Water Reclamation from Urine for Perspective Space Stations. SAE Technical Paper Series no. 961409, 26th International Conference on Environmental Systems, Monterey, CA, July 8-11. Samsonov, N.M., L.S. Bobe, V.M. Novikov, N.S. Farafonov, G.K. Abramov, B.Y. Pinsky, E.I. Grigorov, E.N. Zaitsev, N.N. Protasov, V.V. Komolov, A.I. Grigoriev, and Y.E. Sinyak. 1997. Updated Systems for Water Recovery from Humidity Condensate and Urine for the International Space Station. SAE Technical Paper Series no. 972559, 27th International Conference on Environmental Systems, Lake Tahoe, NV, July 14-17. SSP (Space Station Program). 1995. International Space Station Flight Crew Integration Standard NASA 3000T Document (Aug.). water50005 Rev B. Johnson Space Center, Houston, TX. Verostko, C.E., K. Pickering, F. Smith, N. Packham, J. Lewis, G. Stonesifer, D. Staat, and M. Rosenbaum. 1997. Performance of the Water Recovery System During Phase II of the Lunar-Mars Life Support Test Project. SAE Technical Paper Series no. 972417, 27th International Conference on Environmental Systems, Lake Tahoe, NV, July 14-17.
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