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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES 2 Sources, Treatment, and Monitoring Of Spacecraft Water Contaminants THIS chapter provides an overview of the water reclamation system of the International Space Station (ISS) and a discussion of sources of spacecraft water contamination. Water treatments are discussed in conjunction with contaminant sources, as the treatments also contribute to the contamination. Strategies for monitoring water quality are also discussed. OVERVIEW The ISS is expected to operate for many years, with each crew spending up to 6 months onboard. The prohibitive cost of transporting the large amounts of water needed to support the crew and the impracticality of generating water from fuel cells for missions of this length have led to the requirement that the ISS environmental control and life support system (ECLSS) recycle wastewater to provide water of acceptable quality for potable and personal hygiene use and for oxygen generation. In 1992, the design team for the U.S. space-station life-support systems was directed to assess existing Russian technologies for possible
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES use in developing life support hardware for the ISS (Mitchell et al. 1994). Many components of Russian life support systems (e.g., atmosphere revitalization and water recovery) already have been operational in microgravity. A means of recovering water from humidity condensate has been in use since the Salyut era of the mid-1970s, and a urine-processing system has operated on the Mir station since 1989. The life support system for the ISS will be incorporated in several phases of the assembly sequence. Initially, potable water will be produced from humidity condensate by multifiltration treatment by a Russian assembly housed in the Russian service module. Fuel cell water from the U.S. space shuttle will be transferred to the station after docking. This water, stored in special tanks on the station, will provide an emergency supply. The plan will accommodate up to three crew members. An advanced Russian life support system, involving hygiene-water processing and urine processing will be deployed in the Russian life support module (LSM) of the ISS. At approximately the same time, the ability to reclaim potable water from humidity condensate, hygiene wastewater, and urine distillates (via multifiltration and catalytic oxidation) will be incorporated in the U.S. habitation module of the ISS. Design Drivers Water reclamation systems intended for the ISS and its programmatic predecessors have been designed to deliver specific amounts of product water (Table 2-1) of specified quality. (At the time the ISS system design was begun, no models were available to predict contaminant loads in water produced by the water reclamation systems. Since then, considerable information has been generated from ground-based and in-flight studies, as described later in this chapter, and a predictive model is being generated (D.L. Carter, Marshall Space Flight Center, personal communication, Oct. 13, 1999).) Other considerations in designing the water reclamation systems included shelf life, resupply-return logistics, crew time needed for maintenance, power needed to operate the system, launch weight, and stowage volume. The processing assemblies for the ISS have been designed to support six crew members after assembly is complete. The product-water tank's capacity will be about 120 lb of processed water.
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES TABLE 2-1 ISS Water Requirements Purpose Amount, lb Amount, kg Drinking, food rehydration, oral hygiene 6.2/person/d 2.81/person/d Extravehicular activity 20 9.05 High per-person usage 11.35 over 24 hr 5.14 over 24 hr Hygiene 15.0/person/d 6.79/person/d Hygiene (high usage) 16.0/person over 24 hr 7.24/person over 24 hr Life sciences experiments (with animals) 7.35/d 3.33/d Maximum off-line water-quality analysis 2.2/d 1.00/d Nominal off-line water-quality analysis 1.7/d 0.77/d Oxygen generation 17/d 7.69/d Payload experiments 4.8/experiment d 2.17/experiment d The ISS is designed to support six crew members. Source: Segment Specification for the U.S. On-Orbit, SpecificationNumber SSP 41162E, July 1996, p. 273. Table 2-2 illustrates the water mass balance of the Russian water-processing segments before the completion of the ISS. Total water consumption of a cosmonaut was estimated at approximately 9 lb or 4.1 liters per day (L/d). During the first phase of construction, the Russian service module will reclaim drinking water only from humidity condensate; during the second phase, the service module and the LSM will regenerate potable water from urine. During the second phase, the amount of water supplied by the Russian progress vehicle and the U.S. space shuttle needed to make up the water balance will be lower. ISS Water-Quality Standards Standards for recycled water in a closed spacecraft system have been a matter of debate for many years. Because water aboard the U.S. space shuttle is not recycled (it is generated by onboard fuel cells), ex-
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES TABLE 2-2 Water Mass Balance Estimates of the Russian Water-Processing Segments Water Supply Sources, lb Water Demand (lb/person/d) Source First Phase (SM) Second Phase (SM + LSM) Drinking, food 5.5 Humidity condensate 3.3 3.3 Oxygen generation by electrolysis 2.21 Hygiene water evaporation 0.66 0.66 Personal hygiene 1.1 Water with food 1.1 1.1 Urinal flush 0.66/0.22 Water from storage system 4.44 0.44 Water from WRS-UM NA 2.58 Water from CDRS NA 0.95 Total 9.48/9.0 9.48 9.04 Water mass balance estimates did not consider evaporation or otherwater losses. 85% of the crew water will be regenerated during phase2, whereas only 43% during phase 1. CDRS, carbon dioxide reductionsystem; LSM, life support module; NA, not applicable; SM, servicemodule; WRS-UM, updated system for water reclamation from urine Source: Modified from Samsonov et al. (1997). The units have beenconverted to pounds for comparison with Table 2-1. isting water-quality standards for shuttle water cannot be extended to recycled water, particularly for long ISS missions. In 1986 and 1989, the National Research Council (NRC) Committee on Toxicology reviewed water-quality standards for the National Aeronautics and Space Administration (NASA), and recommend maximum contaminant levels that would protect the health of crews on long space missions (NRC 1986, 1989). This information was used in the design of onboard water treatment and recycling system for the ISS. One critical recommendation was that the integrated ECLSS should be able to assess possible interactions between the air revitalization system and the water reclamation system in terms of contaminants that might arise from one or the other system. The current requirements for ISS water quality are based on standards from the U.S. Public Health Service (PHS 1962) and U.S. Envi-
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES ronmental Protection Agency (EPA 1996) for public drinking water. Standards for water quality are described in Appendix A and in other NASA documents (e.g., the International Space Station Flight Crew Integration Standard, SSP 50005, Rev B, Aug. 1995). Because the Russian segments will initially support water regeneration for the ISS, a review and consensus on Russian water-quality standards is necessary. The standards established for the Mir station generally are less stringent than are U.S. standards: Fewer limits are specified, and those that are specified tend to have higher maximum limits. Also, the disinfectant used for the Mir water-processing system is silver, whereas the biocide for most U.S. systems is iodine. Differences between the two programs in analytical techniques have made direct comparisons difficult; nevertheless, negotiations are currently under way to develop water-quality standards that are acceptable to both partners in the ISS program. Appendix A, Table A-2, compares the proposed standards – which have yet to be accepted officially – of the Russian and U.S. programs. Some detailed descriptions of the water reclamation systems that are currently operating on Mir, planned upgrades for the Russian segments of the ISS, and the planned U.S. integrated water reclamation system functions are provided in Appendix A. SOURCES OF SPACECRAFT WATER CONTAMINATION The water reclamation system for the ISS comprises a unique combination of input and output streams. Waste streams will include urine and urine flush water, humidity condensate, personal hygiene water (body wash), water from general hygiene activities (hand washing, shaving, teeth cleaning), and effluent from the crew health care system (CHeCS). Humidity condensate undoubtedly will have the greatest inherent variability, because it will include contributions from crew metabolism, hygiene activities, food preparation, materials off-gassing, and payload experiments, some of which will involve animals and all of which will vary widely from mission to mission. The nature of the water sources and the extent of closure in the recycling loop have posed substantial challenges for defining product-water specifications that will protect crew health over long periods. In its
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES earlier reviews, NRC (1986, 1989) evaluated NASA's plans for potable-water reclamation, including issues on the small volume of water; the complexity and variability of cabin humidity condensate (the principal source of potable water); the tight interface between cabin air and water systems; the treatment processes for urine and hygiene wastewater and the treatment by-products; the potential accumulation of polar, uncharged organic molecules; the need for toxicologic characterization of unique chemical and microbial by-products; and monitoring and analytical capabilities. Since those reviews, considerable progress has been made in the characterization of source-water contaminants. The results described here come from ground-based and in-flight studies (from Spacelab, shuttle, and Mir missions). Two ground-based test beds in particular have generated a wealth of information on humidity condensate, urine distillates, urine off-gassing products, and wash water – the Water Recovery Test (WRT) at NASA's Marshall Space Flight Center in Huntsville, Alabama, and the Early Human Testing Initiative (renamed the Lunar-Mars Life Support Test Project (LMLSTP)) at NASA's Johnson Space Center in Houston, Texas. The Marshall test bed has been used mainly to assess the performance of the various systems intended for environmental control and life support on space stations. Stages 9 and 10, the two most recent versions of this test bed simulate many aspects of the configuration planned for the ISS. Figure 2-1 is a diagram of the Stage 9 water recovery system. Humans participate in the operation of this system through brief visits to the end-user equipment facility, which includes a shower, hand-washing sink, microwave oven, urine collection and pretreatment unit, condensing heat exchanger, and exercise equipment. The LMLSTP, in contrast, involves human subjects actually living within a closed test chamber that has integrated air and water reclamation systems. Subjects in the chamber donate and use recycled water. Three tests have been completed with this system, the first a 15-d mission involving one crew member, and the second and third involving 30-and 60-d missions, respectively, each including a four-person crew. Results from a 90-d test are not discussed here because water reclamation processes other than those planned for ISS were used. Some information about flight data is available from the 1985 U.S. Spacelab-3 mission; more recent data were generated through observational studies begun in the 1990s on the space shuttle. The advent of
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES FIGURE 2-1 The integrated water recovery system used in Stage 9 of the Marshall WRT. CHeCS, crew health-care system; PCWQM, process-control water-quality monitor; VRA, volatile removal assembly. Source: Holder et al. (1995). U.S.-Russian cooperation has provided an invaluable opportunity to assess the Mir spacecraft water-recycling system, which operates in microgravity. Results from these and other studies form the existing database of the likely chemical constituents of the proposed ISS water system. The major sources of water and their likely contaminants are discussed below. These include likely constituents of human urine, both before and after treatment; humidity condensates and wash water, and the various sources of chemical contaminants to those streams; and chemical by-products that can form as a result of treatment failures or from the use of biocides. Human Urine Untreated Urine The composition of human urine is extremely complex, and it varies widely according to diet, use of medications, and health status. The
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES normal constituents of urine include electrolytes, small-molecular-weight proteins, and metabolites of nutrients and drugs. Typical components include salts of iron, sodium, potassium, magnesium, calcium, chlorides, phosphates, citrates, oxalates, and sulfates. Also present are hormones, vitamins, creatinine, uric acid, and carboxylic acids. Crews in the Apollo, Skylab, and space-shuttle programs have taken drugs to alleviate motion sickness, headache, sleeplessness, constipation, and nasal congestion during flights (Putcha et al. 1994). Because those drugs are likely to be used aboard the ISS, their metabolites will be introduced into the water system via urine. As a result, the chemical composition of urine in the ISS might be somewhat different from the urine used to develop and test ground-based systems where such medications have not been incorporated. Chemical Treatment and Distillation By-Products The water reclamation system planned for the ISS uses chemical pretreatment and distillation in treating urine. Oxone (a commercially developed potassium monopersulfate compound) and sulfuric acid are added to the raw urine to stabilize it, to fix ammoniated species, and to control microbial content. Oxone can oxidize chloride compounds in the urine to form chlorine, which will react directly with several organic compounds to form chlorinated hydrocarbons. This process can generate several nonphysiologic chlorination by-products. Cole et al. (1991) have reported off-gassing of cyanogen chloride, chlorinated ketones, and chlorinated nitriles from treated urine, which probably appeared because of high ammonia and amino acid content in the raw urine. Several distillation technologies have been used in developing the water reclamation system for the space station (including reverse osmosis, thermally integrated membrane evaporation (TIMES), or vapor compression distillation). Early stages of the WRT included TIMES distillation, but later versions included vapor compression distillation, which is the current technology of choice for the ISS. (Urine was pretreated with Oxone and sulfuric acid in both distillation processes.) Despite some minor differences in the composition of the distillate from the two processes, the contaminant load (and its variations over time) were thought to reflect those of the space-station system (Winkler
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES et al. 1983; Verostko 1986; Cole et al. 1991; Carter and Bagdigian 1993). The TIMES distillate included carboxylates, alcohols, ketones, aldehydes, phenols, nitriles, hydrocarbons, and halogenated hydrocarbons. Most compounds could be traced to human metabolism, but some seemed to have resulted from the urine pretreatment process. The constituents produced by vapor compression distillation in Stages 4 and 5 of the WRT are described by Carter et al. (1992). Vapor compression distillation also was used to treat urine in the closed-chamber tests at the Johnson Space Center. Compounds found in the urine distillate samples from the 30-d test included: acetic, butyric, formic, propionic, and lactic acids; ethanol; methanol; 1,1-dichloropropanone; and ibuprofen. Formic acid was present in the highest concentration (13,700 micrograms per liter (µg/L)) (Homan et al. 1997; Verostko et al. 1997). In addition to these results, for the raw distillate of the urine, additional information is available concerning the volatile oxidation products arising from urine pretreatment. In 1989, the NRC expressed serious concerns about concentrations of cyanogen chloride (100 parts per billion (ppb)), reportedly off-gassed in the Marshall WRT study. Off-gassed products from urine treated with Oxone and sulfuric acid (the treatment chosen for the ISS) during a Marshall WRT have been described by Cole et al. (1991). High concentrations of acetone, acetonitrile, methylene chloride, 3-methylbutanal, dimethylamine, propanenitrile, and several other volatile oxidation products were reported. More than a dozen compounds occurred frequently in the off-gassing products from the seven urine samples analyzed. Humidity Condensate Humidity condensate will be an important source water – and probably the most variable – in the ISS water reclamation system. Humidity condensate is collected by the cabin heat exchanger, which is controlled by the spacecraft 's air revitalization system. The chemical constituents will include contaminants released into the cabin air from crew activities, such as by-products of metabolism, food preparation, and hygiene activities (including the use of cleansers and disinfectants); from routine operation of the air revitalization system; from materials and hardware off-gassing; from payload experiments, especially
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES those involving animals; from onboard utility chemicals; and from routine in-flight use of the CHeCS. Some steps in the water recovery process involve liquid-air separations. The air from those steps is vented into the cabin atmosphere and eventually appears in the humidity condensate. As wastewater passes through the multifiltration bed to the volatile removal assembly, for example, small molecular-weight organic compounds in the water undergo catalytic oxidation in the presence of sparged oxygen in a catalytic reactor. Before the effluent is passed to an ion exchange resin, which removes the small-molecular-weight organic compounds, the excess oxygen and other volatile compounds (incomplete oxidation products) are vented to the cabin. Even though some of these airborne contaminants will be removed by “scrubbers ” in the air revitalization system, many will end up in the humidity condensate. Designing an effective water treatment system requires that the chemical constituents of the source water, and the variability of those constituents, be thoroughly characterized. As a corollary, that system also must include ways to evaluate potential toxicologic hazards posed by consuming the product water. The information available regarding the chemical composition of spacecraft humidity condensates is described below. These results came from test bed studies (the WRT and the LMLSTP) and from postflight analyses of samples collected during actual spacecraft missions. The remainder of this section constitutes descriptions of other environmental contributors to condensate aboard spacecraft. Condensate Sample Results Water Recovery Test The water recovery system of the Marshall Space Flight Center WRT includes a facility that contains a shower, handwash, microwave oven, urine collection and pretreatment unit, condensing heat exchanger, and exercise equipment. Tests in which human subjects use this facility have revealed the presence of low-molecular-weight acids, semi-volatile acids, volatile alcohols, purgeable organic compounds, semi-volatile organic compounds, and glycols in the humidity condensate (Cole et al. 1991). The chemical composition of the condensate was
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES highly variable, no doubt reflecting variations both in the ubjects ' activities and in the ambient test environment. Lunar-Mars Life Support Test Project Part of the 30-d test of the Johnson Space Center's LMLSTP, in which wastewater was recycled throughout the test, included chemical characterization of humidity condensate samples. Results from four sets of samples collected are shown in Table 2-3. Total organic carbon (TOC) in the condensate ranged from 45 milligrams per liter (mg/L) to 65 mg/L, and accountability was 97%. Acetone, 2-butoxyethanol, diethyl phthalate, phenol, alcohols, and glycols were present in high concentrations, as were formaldehyde (7.7-12 mg/L) and ethylene glycol (5-12 mg/L). EPA's recommended lifetime maximum exposures are 1 mg/L for formaldehyde and 7 mg/L for ethylene glycol (EPA 1996). Space Shuttle Humidity condensate has been collected on relatively few space-shuttle missions, and most of the samples have been collected during the past 4 or 5 years. One exception was the 1985 STS-51B/ Spacelab-3 mission, which included tests with rodents housed in a new holding facility and analyses of the air revitalization system (Verostko 1986). Although the integrity of the samples collected from the mission was questionable, many organic compounds were identified, including alcohols, amides, amines, carboxylic acids, ethers, esters, ketones, phenols, and thiourea. In 1991 and 1992, samples were collected after four Spacelab missions (STS-40/SLS-1;STS-42/IML-1;STS-50/USML-1;STS-47/SL-J); however, the long delays after landing until samples could be collected undoubtedly affected their chemical composition. Finally, routine assessments of atmospheric quality aboard shuttle missions have revealed the presence of a wide spectrum of organic compounds that could well appear in the humidity condensate (James et al. 1994). The first in-flight humidity condensate samples were collected on two shuttle missions, STS-45 and STS-47, in 1992; additional samples were collected from STS-68 and from the Mir. Organic compounds found in the 9 samples collected on the STS-45 and STS-47 missions are listed in Table 2-4 (Muckle et al. 1993).
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES TABLE 2-10 Organic Contaminants in Processed Waters During the 60-d Johnson Space Center Chamber Study Concentration, µg/L Compound Minimum Maximum Frequencya Iodoform 1.6 4.8 40 Methyl sulfone 0.6 54.5 38 Di-n-butyl phthalate 0.1 2.3 36 Toluene 1.01 9.53 34 2-Ethyl-1-hexanol 0.4 12.4 33 Formaldehyde 2 13.8 30 Benzaldehyde 0.1 0.8 24 1-Methyl-2-pyrrolidinone 0.3 7.4 21 Benzyl alcohol 0.8 7 21 Diiodomethane 0.4 1.8 19 Diisopropyl adipate 0.4 0.9 17 Dodecamethylcyclohexasiloxane 0.5 1.7 13 Acetate 0.14 3.97 11 Bis-2-ethylhexyl phthalate 0.1 1.7 11 4-Hydroxy-4-methyl-2-pentanone 0.6 3.4 10 Methanol 101 233 8 1-Formylpiperidine 0.1 0.6 7 Squalene 0.9 3.9 6 Decamethylcyclopentasiloxane 0.1 0.2 5 Diethyl phthalate 0.2 0.4 5 Lactate 0.18 1.1 4 Oxalate 0.23 0.41 4 sec-Phenethyl alcohol 0.1 0.2 4 Acetone 4.64 6.3 3 Acetophenone 0.1 0.3 3 Benzothiazole 0.1 0.7 3 Pentacosane 0.3 1.2 3 Phenol 0.7 1 3 2-(2-Butoxyethoxy)ethanol 0.4 0.8 2 2-Butoxythanol 3.1 3.2 2 2-Ethylhexanoic acid 1.7 2.1 2 Monomethyl phthalate 4.8 4.8 2 N,N-Dimethylbenzylamine 0.6 0.6 2 Octamethylcyclotetrasiloxane 0.4 0.6 2 Octanoic acid 2.6 2.9 2 Tris-2-chloroethyl phosphate 0.9 1.5 2 Benzylbutyl phthalate 3.6 3.6 1 Bis-2-ethylhexyl adipate 0.8 0.8 1 n-Butyl palmitate 5.3 5.3 1 Butyl stearate 10.7 10.7 1 1,4-Diacetylbenzene 0.3 0.3 1 Neomenthol 0.2 0.2 1 2-Phenyl-2-propanol 0.5 0.5 1 2-Propanol 154 154 1 Tetramethylsuccinonitrile 0.4 0.4 1 Tributyl phosphate 0.5 0.5 1 Urea 302 302 1 Total organic carbon 87 1,850 a Frequency of detection in 68 samples. Source: J. Schultz and colleagues, Wyle Laboratories, personal communication,Sept. 1997.
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES returned to test subjects for use. The water recovery system processed pretreated urine flush water; an ersatz sample of CHeCS waste; ersatz animal condensate; humidity condensate; ersatz equipment off-gas; ersatz fuel cell water; and wet shave, personal hygiene, and oral hygiene water. The results in general indicated no accumulation of contaminants in the product water (Carter 1997). When they become available, detailed analysis data on organic species will be reported. The issues involved with developing appropriate water-processing hardware and treatment technologies are complex. Because of the unique nature of the input water to the ISS water processor system, NASA has placed strong emphasis on characterizing the nature of potential contaminants and on assessing variations in the influent streams as thoroughly as possible. Several efforts have been made to predict the chemical makeup of source waters to the ISS water processor system. Ground-based test beds, such as the WRT and the LMLSTP, can simulate only some aspects of ISS input water. Humidity condensate samples have been collected from a few space-shuttle and Mir missions, but the constituents of these spacecraft samples have not been compared with those of the ground-based test beds. A composite compila-
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES tion of wastewater data from various sources has been attempted (Carter 1998). Despite substantial variability in TOC accountability between shuttle and Mir missions, and the very poor accountability from the Mir product water (partly due to detection limits issues), the results gathered so far from ISS simulated wastewater streams and in-flight raw and processed water samples indicate that the organic compounds that are present are vastly different from the list of target compounds developed by EPA for public drinking water. MONITORING WATER CONTAMINANTS Conductivity is the only process control monitoring currently done aboard Mir in its condensate processor system. During the ISS early assembly phase, to monitor the water quality, the Russian segment service module will accommodate U.S.-provided water-quality monitoring hardware for in-flight off-line monitoring with provisions for archiving water samples for ground-based analysis. The U.S. program proposes several strategies for water monitoring after the ISS is assembled. Source-Water Monitoring As noted by the NRC (1992), the drivers for designing and operating any potable-water processor will depend on the organic and inorganic constituents of the raw source water. Adequate specifications for ensuring the quality of the reclaimed or recycled water do not exist outside of NASA, and thus attention must be directed to the definition of source water. Because the content of source waters aboard` spacecraft cannot be predicted reliably from ground-based experiments, the NRC recommended that actual humidity condensate and other raw waters be collected from short- and long-term space flights. The waters should be thoroughly analyzed, and their variability should be clarified. This task also is important in terms of defining potential health hazards from the use of water aboard spacecraft. Described below are monitoring strategies derived from continuing tests of isolated and integrated water-recovery systems conducted at
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES the Marshall Space Flight Center (Bagdigian et al. 1991; Carter et al. 1992; Homan et al. 1994; Holder et al. 1995), analyses of humidity condensate collected from the space shuttle (Muckle et al. 1993; Straub et al. 1995) and from Mir (Pierre et al. 1996), and analyses of samples from a human-rated life-support chamber (the LMLSTP) (J Schultz, Wyle Laboratories, personal communication, Sept. 1997). In-Line Monitoring and Process Control Conductivity is the only aspect of water quality that is monitored routinely aboard Mir and planned for the early phase 2 of the ISS assembly in the Russian service module. In the current proposed configuration of the ISS, an in-line process control water-quality monitor (PCWQM) will assess conductivity, iodine, pH, and TOC. (Product-water TOC should be less than 0.5 mg/L.) If the parameters are within acceptable limits, the effluent is transferred to the potable-water subsystem; if not, the water is shunted upstream of the multifiltration subsystem for reprocessing (see Appendix A, Figure A-3). Current plans for monitoring ISS water quality after completion of the ISS (plans that are subject to revision) are ouflined in Appendix A, Table A-3. Off-Line Monitoring The ISS will have one tank, and if the water limit fails the criteria by the on-line monitor it will be reprocessed. At present, only conductivity and other surrogate quality measures can be used for routine in-line water-quality monitoring. (A water-quality monitor that can measure conductivity, TOC, and iodine – all pass/fail criteria for potability – has been tested successfully in Stage 10 of the Marshall WRT (Carter 1997).) A comprehensive evaluation (complete characterization) of the product water might be needed after every recycling to ensure that the technologies can effectively remove compounds that are potentially hazardous to the health of crew members. Even though organic and inorganic constituents will be removed by the series of granular activated-carbon and ion-exchange beds, and low-molecular-weight compounds will undergo catalytic oxidation at the volatile removal assembly, trace contaminants could produce io-
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES dinated organic compounds through reactions with residual iodine in the water. Because such disinfection by-products have neither been chemically characterized nor assessed for potential toxicity, the precursor materials that could contribute to the formation of the by-products should be well understood. Complete characterizations of product water, particularly its organic constituents, will require off-line analyses, which in turn require that hardware and analytical methods be developed for use in space. Progress toward that goal was provided by the 60-d test of the LMLSTP in a human-rated regenerative life support chamber at Johnson Space Center (Meyers et al. 1997). This test bed was used to develop a comprehensive strategic tier for monitoring aspects of processed-water quality off-line, such as tests for process verification, and selective and complete characterization (Table 2-11). Even though several forms of water-quality monitoring hardware initially were proposed by the CHeCS for providing detailed in-flight analyses, programmatic and logistical considerations have been restricted to only a few for off-line monitoring (Table 2-12). TABLE 2-11 Water Analyses for Phase IIA of the Lunar-Mars Life Support Test Project Water Verification Potable Characterizationa Complete Characterizationb Conductivity Alcohols Anions Iodine, iodide Amines Cations TOC Carboxylates Color pH Formaldehyde Glycols Nonvolatile organic compounds Mercury Organic acids Metals Semivolatile organic compounds Turbidity Volatile organic compounds Urea a Includes water verification. b Includes water verification and potable characterization. TOC, total organic carbon Source: Master Protocol for the Participation of Human Test Subjectsin Phase IIA of the Early Human Testing Initiative, Crew and ThermalSystems Division, Johnson Space Center, Oct. 16, 1996.
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES TABLE 2-12 ISS Water Monitoring Capabilities by Crew Health Care Systems Instrument Parameter Purpose TOC analyzer TOC, TIC, TC, pH, conductivity Assess organic load in reclaimed water Sampler and archiver NA Sample from water systems for inflight and ground analyses Spectrophotometer Color, turbidity, iodine species; UV/Vis spectra; wet chemistry Assess general water quality and U.S. biocide concentrations and effectiveness The first two items will support monitoring during the early phasesof ISS when the Russian service module and life support modules willprocess water. NA, not applicable; TC, total carbon; TIC, total inorganic carbon;TOC, total organic carbon; UV/Vis, ultraviolet-visible Sources: International Space Station Medical Operations RequirementsDocument (ISS MORD), Document Number SSP 50260, Baseline, January1998; and Crew Health Care System (CHeCs) GFE Specification, InternationalSpace Station, Revision Basic, June 1999, NASA Johnson Space Center(Draft) Document Number SSP 50470. SUMMARY The joint U.S.-Russian space program was expanded to include collecting samples of condensate and reclaimed cold and hot water during flights, beginning with Mir-18 in 1995 and continuing through Mir-25 in March 1998. Samples were collected with hardware supplied by the U.S., and they were analyzed by both NASA (at the Johnson Space Center) and the Russian Space Agency (at the Institute of Biomedical Problems). Results have shown that the reclaimed water meets all Russian water-quality specifications (except for TOC) and most NASA standards (except for some halogenated hydrocarbons). However, only 5% TOC in samples collected from Mir could be identified with available analytical techniques.
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES To date, only humidity condensate has been used to regenerate potable water during flight in Mir. Information on water recovered from Mir urine processors under microgravity conditions is not available, and the only microgravity opportunities to test the technologic aspects of water reclamation are Mir missions. Conceptual and functional differences between the U.S. and Russian approaches, as well as logistical problems in exchanging information about technology, are challenging. In addition, the materials used in the Mir modules might not be the same as those planned for the ISS, and Mir information is 7-10 years old. Results from a ground-based, human-rated chamber facility at Johnson Space Center, which had integrated systems for air revitalization and water recovery, provided useful supplements for microgravity tests from a systems operations point of view. Several issues remain to be resolved for the ISS program, particularly differences between the Russian and U.S. systems in the quantity of water to be produced and in the quality standards for that water. However, in the past 2 years, as a result of periodic technical interchange meetings between Russian and U.S. scientists, several issues concerning water quality, monitoring, and quantity are being resolved. The Russian water processor that will be launched during phase 2 (on the Russian service module) will have a slightly different design from that on Mir, and water quality will be judged solely on the basis of conductivity. Planned modifications to the Russian urine-processing system include the distillation process, the design and function of the heat pump, optimization of the air flow rate, and increases in capacity and reliability. Weekly Mir system status updates provided to NASA on the performance of both the condensate processors (SRV-K and the SRV-U) have provided a mechanism to assess confidence in the systems' performance. Long-term concerns include the build-up of chemical contaminants that are difficult to remove during water processing and the possibility of progressive microbial colonization of the multifiltration resin systems and distribution systems. Concerns also have been raised about the possibility of the generation of iodine-resistant microorganisms and their metabolic products in the water system. Finally, the planned in-flight water-quality monitoring hardware is limited and perhaps far from mature in terms of its microgravity compatibility testing and flight qualifications.
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES Combinations of extensive ground-based testing completed so far involving human crews and risk mitigation experiments aboard the shuttle and Mir have provided additional information on processes and processors with which to provide water that poses minimal long-term health risks to crew members. Comprehensive comparisons of those chemicals found in regenerated water from all forms of tests should form the basis for a hazard assessment database for specific chemical constituents in product water. This will be a complex task, as a variety of issues must be considered, including differences in the exposure scenarios between ground-based and in-flight studies (i.e, microgravity, use of certain drugs); differences in exposure among in-flight and ground-based studies (i.e., duration, cabin materials); delays between sampling and analysis of in-flight water; and better technology for more recent tests. REFERENCES Bagdigian, R.M., M.S. Traweek, and G.K. Griffith. 1991. Phase III Integrated Water Recovery Testing at MSFC: Partially Closed Hygiene and Open Potable Loop Results and Lessons Learned. SAE Technical Paper Series no. 911375, 21st International Conference on Environmental Systems, San Francisco, CA, July 1991. Barkley, R., C. Hurst, A. Dunham, J. Silverstein, and G.M. Brion. 1992. Generation of Iodine Disinfection By-products (IDPs) in a Water Recycle System. SAE Technical Paper Series no. 921362, 22nd International Conference on Environmental Systems, Seattle, WA, July 1992. Barkley, R., A. Dunham, J. Silverstein, and C. Hurst. 1993. Iodine Disinfection By-products (IDPs) Generated in Water from Selected Organic Precursor Compounds. SAE Technical Paper Series no. 922097, 23rd International Conference on Environmental Systems, Colorado Springs, CO, July 1993. Carter, D.L. 1997. Phase III Integrated Water Recovery Testing at MSFC: International Space Station Recipient Mode Test Results and Lessons Learned. SAE Technical Paper Series no. 972375, 27th International Conference on Environmental Systems, Lake Tahoe, NV, July 14-17, 1997. Carter, D.L. 1998. Waste Water Characterization for the ISS Water Processor. SAE Technical Paper Series no. 981616, 28th International Conference on Environmental Systems, Danvers, MA, July 13-16, 1998. Carter, D.L., and R.M. Bagdigian. 1993. Phase III Integrated Water Recovery Testing at MSFC: Single-loop Test Results and Lessons Learned. SAE Tech-
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METHODS FOR DEVELOPING SPACECRAFT WATER EXPOSURE GUIDELINES Space Physiology and Medicine, 3rd Ed., A.E. Nicogossian, C.L. Huntoon, and S.L. Pool, eds. Philadelphia: Lea & Febiger. 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, 1997. Straub, J.E., J.R. Schultz, W.F. Michalek, and R.L. Sauer. 1995. Further Characterization and Multifiltration Treatment of Shuttle Humidity Condensate. SAE Technical Paper Series no. 951685, 25th International Conference on Environmental Systems, San Diego, CA, July 1995. SSP (Space Station Program). 1995. International Space Station Flight Crew Integration Standard NASA STD 3000T. SSP 50005 Rev. B. Aug. Johnson Space Center, Houston, TX. SSP (Space Station Program). 1996. Segment Specification for the US On-Orbit. SSP 41162E, p. 273. July. Johnson Space Center, Houston, TX. SSP (Space Station Program). 1998. International Space Station Medical Operations Requirements Document (ISS MORD). SSP 50260. Jan. Johnson Space Center, Houston, TX. SSP (Space Station Program). 1999. Crew Health Care System (CheCs) GFE Specification, International Space Station, Revision Basic. SSP 50470. July. Johnson Space Center, Houston, TX. Thorstenson, Y.R., D.S. Janik, and R.L. Sauer. 1987. Medical Effects of Iodine Disinfection Products in Spacecraft Water . SAE Technical Paper Series no. 871490, 17th International Conference on Environmental Systems, July 1987. Verostko, C.E. 1986. Space Station Water Sources. Paper presented at the Space Station Water Quality Conference, Lyndon B. Johnson Space Center, Houston, TX, July 1-2, 1986. 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 1997. Winkler, H.E., C.E. Verostko, and G.F. Dehner. 1983. Urine Pretreatment for Water Processing Systems. SAE Technical Paper Series no. 831113.
Representative terms from entire chapter: