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This paper continues previous work on pyrolysis processing of solid wastes for spacecraft and planetary surface applications. A prototype microwave pyrolyzer apparatus was designed, constructed and tested. Experiments were done with cellulose, wheat straw and two formulations of a feces simulant. A central microwave absorber was used consisting of a quartz tube filled with activated carbon. The pyrolyzer included a primary pyrolysis zone and a secondary cracking zone consisting of a SiC bed. The cracking zone temperature ranged from ~ 850 to 1000 °C. The sample was inserted into the (primary) microwave heating zone after the cracking bed temperature was stabilized to ~ 950 °C. Analysis of the gas products was performed by both FTIR spectroscopy and mass spectrometry. The sample sizes were 15-20 g for wheat straw, 40 g for cellulose and 100 g for the feces simulants. The cellulose sample was not run to completion, but was interrupted to provide photographic evidence that microwave heating using a central microwave absorber results in pyrolysis beginning near the center of the sample and proceeding in an outward fashion. For the wheat straw and feces simulant samples, it was found that, on a per-gram basis, the yields of ethylene, methane, and hydrogen were significantly higher than a previous pyrolyzer that was based on a modified domestic microwave oven. This result was mainly attributed to the presence of a separate cracking zone in the current pyrolyzer.

This paper continues previous work on pyrolysis processing of solid wastes for spacecraft and planetary surface applications. A domestic microwave oven was modified for use in this work for scoping studies in which the effects of sample composition, use of central microwave absorbers, and secondary pyrolysis of liquids were studied. Experiments were done with wheat straw and various formulations of a feces simulant. The microwave absorbers examined included activated carbon and char produced from previous experiments. The addition of a separate microwave-heated secondary pyrolysis zone was also examined as a means of reducing the liquid product yields. In general, the feces simulants had similar pyrolysis yields when compared to wheat straw for the char and total gas yields, but individual gas yields were different. For example, the feces simulants produced significantly more ethylene, larger amounts of methane, and smaller amounts of carbon oxides (CO + CO2). This can be largely explained by the differences in elemental compositions. A comparison was also made of the microwave-assisted pyrolysis of feces simulants of variable moisture contents (0-60 wt. %). The higher moisture contents (40-60 wt. %) result in a delay for the onset of pyrolysis and a higher energy demand per gram of sample, as might be expected. However, at lower moisture contents, such as the 20 wt. % water for the baseline sample, it was found that the overall energy demand appeared to be lower than for the dried sample, perhaps due to the more efficient absorption of microwave energy.

There has recently been an increased interest in using pyrolysis of mixed solid wastes in space or on planetary surfaces to produce methane for applications in propulsion and for power generation using fuel cells. This paper involves a review of previous pyrolysis results collected at Advanced Fuel Research, Inc. (AFR) and elsewhere to determine how the pyrolysis conditions and feedstock composition affect methane yields. In general, the production of methane from primary pyrolysis of most biomass materials is pretty modest, 0.1 to 2.5 wt. % for a wide range of materials, with an average slightly above 1.2 wt. % (dry, ash-free basis). The primary pyrolysis yield variations for methane (and other species) with biomass sample type are well described using a simple Neural Network model. In pyrolysis experiments that include significant secondary reactions (e.g., tar cracking), the methane yield can be increased by a factor of 2-3. The methane yield can also be increased significantly by increasing the plastic component of the mixed waste stream (e.g., by the addition of polyethylene), but would be unlikely to exceed 15 wt. % by conventional, low-pressure pyrolysis of a typical mixed waste stream. The use of high pressure (>500 psig) pyrolysis in pure hydrogen is one approach that could be used to increase the methane yield even further. However, this approach would require a much heavier reactor unit, high pressures, and the associated safety concerns. An alternative pathway to higher methane yields would be to oxidize the waste completely to carbon dioxide and water and use the Sabatier reaction to convert the carbon dioxide to methane.

Solid Waste handling and management in space habitats poses serious challenges for long duration human space missions. These wastes typically contain a high quantity of plastic from packaging as well as personal hygiene wastes, wet and dry wipes, gloves, duct tape, and unused food items. The unused food and personal hygiene wastes present substrates for growth of microorganisms that can seriously affect astronaut health and consequently mission success. The heat melt compaction process uses heat to sterilize and dry the waste, and the plastic content to bond and encapsulate the various waste items into a hard tile. The tile that is produced in the heat melt compaction process is tough, extremely compact, and has a predictable shape that allows the efficient use of very limited spacecraft storage volume. The encapsulation of the waste in the melted plastic isolates the growth substrate from spacecraft cabin air to prevent reinoculation of the waste. Plastic wastes contain a high percentage of hydrogen which is considered a desirable material for radiation shielding because it does not produce secondary radiation. Collaborative work with MSFC personnel on evaluating the effectiveness of tiles produced in the Heat Melt Compactor as a shielding material against radiation is in progress. Progress on the development of the next generation Heat Melt Compactor hardware is also presented.

In this paper, results of further work on pyrolysis processing of mixed solid wastes for spacecraft applications are reported. A domestic microwave oven was modified for scoping studies in which the effects of sample size and the use of distributed versus central microwave absorbers were studied. Experiments were done with wheat straw and included those in which the sample was rotated during pyrolysis in order to improve heating uniformity. The experiments using central microwave absorbers of various compositions included a ferrite rod, a quartz tube filled with activated carbon, and silicon carbide. The ability to monitor the sample temperature and sample heating uniformity during microwave heating was demonstrated. A comparison was made with conventional pyrolysis experiments in an electrically heated furnace to a similar final temperature. In general, it was found that microwave heating reduced the energy demand by about 50% and increased the yield of gas products by about 100%, while reducing the char yield about 20%.

This paper addresses the feasibility of integrating pyrolysis, tar cracking and oxidation steps into a compact, efficient system for processing of spacecraft solid wastes. This work demonstrated that it is feasible to pyrolyze a representative spacecraft solid waste sample and crack and/or oxidize the effluent gases using in a microwave assisted, close-coupled integrated reactor system. The net result is a significant reduction (estimated at 70% lower) in the total energy requirement (per gram of sample) when compared to conventional heating and a simpler, more compact apparatus. Although a formal ESM calculation was not done for the preliminary reactor system due to its small size, by analogy to literature studies comparing microwave heating to conventional heating, a significant reduction in ESM is also expected for a full scale prototype. The need for waste processing varies greatly depending on the mission scenario. Another goal of the project was to demonstrate that a Microwave-Assisted Pyrolysis (MAP) approach can meet the short term, intermediate term, and long term objectives of NASA for closed-loop life support. Microwave-Assisted Pyrolysis can perform the near term objectives of volume reduction, stabilization, and water recovery, the intermediate term objective of recovering additional amounts of water and oxygen from waste materials, and the long term objective of a Controlled Ecological Life Support System (CELSS) and In-Situ Resource Utilization (ISRU).

Long term storage of unprocessed biological wastes and human wastes can present major health issues and a loss of potential resources. Space vehicles and planetary habitats are typically resource-scarce or resource-limited environments for long-term human habitation. To-date, most of the resources will need to be supplied from Earth, but this may not be possible for long duration human exploration. Based on present knowledge, there is only very limited in-situ resources on planetary habitats. Hence, the opportunity to "live off the land" in a planetary habitat is limited. However, if we assume that wastes generated by human explorers are viewed as resources, there is great potential to utilize and recycle them, thereby reducing the requirements for supply Earth and enabling the "live off the land" exploration scenario. Technologies used for the recovery of resources from wastes should be reliable, safe, easy to operate, fail-proof, modular, automated and preferably multifunctional in being capable of handling mixed solid and liquid wastes. For a lunar habitat, energy does not appear to be the major driving factor amongst the technologies studied. Instead, reliability appears to be more important[1] . This paper reports studies to date on drying technologies to remove water from solid wastes and brines. Experimental performance data obtained for recovery water from wastes and brine are presented. Simplicity of operation of hardware and energy efficiency are discussed. Some improvements and modifications to hardware were performed. Hopefully, this information will assist in future efforts in the "downselection" of technologies for recovery of water and resources from solid wastes and brines.

Phaseolus vulgaris tolerates low (48 mM NaCl), but not higher levels (72 and 96 mM NaCl) of salinity stress. At the low salinity stress, there is an initial delay in development (morphogenetic shift) of the leaves. Salinity affects shoot growth more than root growth. Osmotic adjustment to salt stress results in an increased water content in the leaves. Our results suggest that two major physiological traits enable the plants to tolerate salinity: (a) compensatory growth following adjustment to salinity, and (b) ability to increase both leaf area ratio (LAR) and net assimilation rate (NAR) to achieve this increased growth. These characteristics are important physiological traits which can be used in screening for potential salt-tolerant lines of beans and other crop plants.

Newly outlined missions in the Space Exploration Initiative include extended human habitation on Mars. During these missions, large amounts of waste materials will be generated in solid, liquid and gaseous form. Returning these wastes to Earth will be extremely costly, and will therefore likely remain on Mars. Untreated, these wastes are a reservoir of live/dead organisms and molecules considered to be "biomarkers" i.e., indicators of life). If released to the planetary surface, these materials can potentially confound exobiology experiments and disrupt Martian ecology indefinitely (if existent). Waste management systems must therefore be specifically designed to control release of problematic materials both during the active phase of the mission, and for any specified post-mission duration. To effectively develop waste management requirements for Mars missions, planetary protection guidelines must first be established. While previous policies for Apollo lunar missions exist, it is anticipated that the increased probability of finding evidence of life on Mars, as well as the lengthy mission durations will initially lead to more conservative planetary protection measures. To facilitate the development of overall requirements for both waste management and planetary protection for future missions, a workshop was conducted to identify how these two areas interface, and to establish a preliminary set of planetary protection guidelines that address waste management operations. This paper provides background regarding past and current planetary protection and waste management issues, and their interactions. A summary of the recommended planetary protection guidelines, anticipated ramifications and research needs for waste management system design for both forward (Mars) and backward (Earth) contamination is also provided.

Carbon nanotubes (CNTs) possess extraordinary properties such as high surface area, ordered chemical structure that allows functionalization, larger pore volume, and very narrow pore size distribution that have attracted considerable research attention from around the world since their discovery in 1991. The development and characterization of an original and innovative approach for the control and elimination of gaseous toxins using single walled carbon nanotubes (SWNTs) promise superior performance over conventional approaches due to the ability to direct the selective uptake of gaseous species based on their controlled pore size, increased adsorptive capacity due to their increased surface area and the effectiveness of carbon nanotubes as catalyst supports for gaseous conversion. We present our recent investigation of using SWNTs as catalytic supporting materials to impregnate metals, such as rhodium (Rh), palladium (Pd) and other catalysts. A protocol has been developed to oxidize the SWNTs first and then impregnate the Rh in aqueous rhodium chloride solution, according to unique surface properties of SWNTs. The Rh has been successfully impregnated in SWNTs. The Rh-SWNTs have been characterized by various techniques, such as TGA, XPS, TEM, and FTIR. The project is funded by a NASA Research Announcement Grant to find applications of single walled nanocarbons in eliminating toxic gas Contaminant in life support system. This knowledge will be utilized in the development of a prototype SWNT KO, gas purification system that would represent a significant step in the development of high efficiency systems capable of selectively removing specific gaseous for use in regenerative life support system for human exploration missions.

The wheat straw, an inedible biomass that can be continuously produced in a space vehicle has been used to produce activated carbon for effective control of NOx emissions from the incineration of wastes. The optimal carbonization temperature of wheat straw was found to be around 600 degrees C when a burnoff of 67% was observed. The BET surface area of the activated carbon produced from the wheat straw reached as high as 300 m2/g. The presence of oxygen in flue gas is essential for effective adsorption of NO by activated carbon. On the contrary, water vapor inhibits the adsorption efficiency of NO. Consequently, water vapor in flue gas should be removed by drying agents before adsorption to ensure high NO adsorption efficiency. All of the NO in the flue gas was removed for more than 2 h by the activated carbons when 10% oxygen was present and the ratio of carbon weight to the flue gas flow rate (W/F) was 30 g min/L, with a contact time of 10.2 s. All of NO was reduced to N2 by the activated carbon at 450 degrees C with a W/F ratio of 15 g min/L and a contact time of 5.1 s. Reduction of the adsorbed NO also regenerated the activated carbon, and the regenerated activated carbon exhibited an improved NO adsorption efficiency. However, the reduction of the adsorbed NO resulted in a loss of carbon which was determined to be about 0.99% of the activated carbon per cycle of regeneration. The sufficiency of the amount of wheat straw in providing the activated carbon based on a six-person crew, such as the mission planned for Mars, has been determined. This novel approach for the control of NOx emissions is sustainable in a closed system such as the case in space travel. It is simple to operate and is functional under microgravity environment.

The use of the activated carbon produced from rice hulls to control NOx emissions for future deep space missions has been demonstrated. The optimal carbonization temperature range was found to be between 600 and 750 degrees C. A burnoff of 61.8% was found at 700 degrees C in pyrolysis and 750 degrees C in activation. The BET surface area of the activated carbon from rice hulls was determined to be 172 m2/g when prepared at 700 degrees C. The presence of oxygen in flue gas is essential for effective adsorption of NO by activated carbon. On the contrary, water vapor inhibits the adsorption efficiency of NO. Consequently, water vapor in flue gas should be removed by drying agents before adsorption to ensure high NO adsorption efficiency. All of the NO in the flue gas was removed for more than 1.5 h when 10% oxygen was present and the ratio of the carbon weight to the flue gas flow rate (W/F) was 15.4 g min/L. Reduction of the adsorbed NO to form N2 could be effectively accomplished under anaerobic conditions at 550 degrees C. The adsorption capacity of NO on the activated carbon was found to be 5.02 mg of NO/g of carbon. The loss of carbon mass was determined to be about 0.16% of the activated carbon per cycle of regeneration if the regeneration occurred when the NO in the flue gas after the carbon bed reached 4.8 ppm, the space maximum allowable concentration. The reduction of the adsorbed NO also regenerated the activated carbon, and the regenerated activated carbon exhibited an improved NO adsorption efficiency.

The elemental composition of food consumed by astronauts is well defined. The major elements carbon, hydrogen, oxygen, nitrogen and sulfur are taken up in large amounts and these are often associated with the organic fraction (carbohydrates, proteins, fats etc) of human tissue. On the other hand, a number of the elements are located in the extracellular fluids and can be accounted for in the liquid and solid waste fraction of humans. These elements fall into three major categories - cationic macroelements (e.g. Ca, K, Na, Mg and Si), anionic macroelements (e.g. P, S and Cl and 17 essential microelements, (e.g. Fe, Mn, Cr, Co, Cu, Zn, Se and Sr). When provided in the recommended concentrations to an adult healthy human, these elements should not normally accumulate in humans and will eventually be excreted in the different human wastes. Knowledge of the partitioning of these elements between the different human waste fractions is important in understanding (a) developing waste separation technologies, (b) decision-making on how these elements can be recovered for reuse in space habitats, and (c) to developing the processors for waste management. Though considerable literature exists on these elements, there is a lack of understanding and often conflicting data. Two major reasons for these problems include the lack of controlled experimental protocols and the inherently large variations between human subjects (Parker and Gallagher, 1988). We have used the existing knowledge of human nutrition and waste from the available literature and NASA documentation to build towards a consensus to typify and chemically characterize the various human wastes. It is our belief, that this could be a building block towards integrating a human life support and waste processing in a closed system.

The success of physico-chemical waste processing and resource recovery technologies for life support application depends partly on the ability of gas clean-up systems to efficiently remove trace contaminants generated during the process with minimal use of expendables. Highly purified metal-impregnated carbon nanotubes promise superior performance over conventional approaches to gas clean-up due to their ability to direct the selective uptake gaseous species based both on the nanotube s controlled pore size, high surface area, and ordered chemical structure that allows functionalization and on the nanotube s effectiveness as a catalyst support material for toxic contaminants removal. We present results on the purification of single walled carbon nanotubes (SWCNT) and efforts at metal impregnation of the SWCNT's.

This paper presents the results from a joint research initiative between NASA Ames Research Center and Lawrence Berkeley National lab. The objective of the research is to produce activated carbon from life support wastes and to use the activated carbon to adsorb and chemically reduce the NO{sub x} and SO{sub 2} contained in incinerator flue gas. Inedible biomass waste from food production is the primary waste considered for conversion to activated carbon. Results to date show adsorption of both NO{sub x} and SO{sub 2} in activated carbon made from biomass. Conversion of adsorbed NO{sub x} to nitrogen has also been observed.

Summary Photosynthesis, the conversion of light energy into chemical energy, is a critical biological process, whereby plants synthesize carbohydrates from light, carbon dioxide (CO 2 ) and water. The influence of gravity on this biological process, however, is not well understood. Thus, centrifugation was used to alter the gravity environment of Euglena gracilis grown on nutritive agar plates illuminated with red and blue light emitting diodes. The results showed that hypergravity (up to 10× g ) had an inhibitory effect on photosynthetic CO 2 fixation. Chlorophyll accumulation per cell was essentially unaffected by treatment; however, Chl a /Chl b ratios decreased in hypergravity when compared to 1×g controls. Photosynthesis in Euglena appears to have limited tolerance for even moderate changes in gravitational acceleration.

This paper presents the results from a joint research initiative between NASA Ames Research Center and Lawrence Berkeley National lab. The objective of the research is to produce activated carbon from life support wastes and to use the activated carbon to adsorb and chemically reduce the NO(sub x) and SO(sub 2) contained in incinerator flue gas. Inedible biomass waste from food production is the primary waste considered for conversion to activated carbon. Results to date show adsorption of both NO(sub x) and SO(sub 2) in activated carbon made from biomass. Conversion of adsorbed NO(sub x) to nitrogen has also been observed.

Terraforming of Mars is the long-term goal of colonization of Mars. However, this process is likely to be a very slow process and conservative estimates involving a synergic, technocentric approach estimate that it may take around 10,000 years before the planet can be parallel to that of Earth and where humans can live in open systems. Hence, any early missions will require the presence of a closed life support system where all wastes, both solids and liquids, will need to be recycled or where all consumables will need to be supplied. The economics of both are often a matter of speculation and conjecture, but some attempt is made here to evaluate the choice. If a choice is made to completely resupply and eject the waste mass, a number of unknown issues are at hand. On the other hand, processing of the wastes, will enable predictability and reliability of the ecosystem. Solid wastes though smaller in volume and mass than the liquid wastes contains more than 90% of the essential elements required by humans and plants. Further, if left unprocessed they present a serious risk to human health. This paper presents the use of well established technology in processing solid wastes, ensuring that the biogeochemical cycles of ecosystems are maintained, reliability of the closed life support system maintained and the establishment of the early processes necessary for the permanent presence of humans on Mars.

Anionic surfactants are the major class of surfactants used in detergent, laundry and related industries. Hence, they are a major contaminate of both domestic and industrial waste streams. Lettuce (Lactuca sativa cv Waldemann's Green) was grown in nutrient solutions with the addition of the anionic surfactant, Igepon TC-42. The toxic response of lettuce to Igepon was that the roots turned brown and became necrotic within 24 h following exposure. Growth was supressed for approximately 4 days following exposure to concentration greater than 0.35 mM; new roots formed rapidly and growth resumed. When fresh plants were transferred to the solutions containing Igepon 48 h following introduction of the surfactant no signs of toxicity were observed. This would indicate that either the first series of plants absorbed the toxic material or the Igepon was decayed or degraded in the nutrient solution. The rapid recovery of plants from this stress suggests the potential of a wide range of strategies that could be developed for utilizing waste streams containing anionic surfactants.

Centre for Add Zone Studies, U. C. N. W., Bangor, Gwynedd LL57 2UW, Wales, United Kingdom Manuscript received 21 April1986, revised 3 September 1987, accepted 13 January 1988 THE Fiske- Subbarow method1 for the quantitative determination of inorganic phosphate suffers from the lack of stability of the blue colour of the reduced phosphomolybdate complex. The method was modified by Lindemann2 using a combination of hydrazine sulphate and stannous chloride, by Martland and Robison3 using quinols in sodiumsulphate and by Ames5 using ascorbic acid as the reductant. Further modifications were carried out by Delory4 and King5 , and the latter has been successfully used by Khan and Rao6.