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PubMed1998

Azolla-Anabaena symbionts and microbial mat as nitrogen-fixing biocatalysts for bioregenerative space life support.

This study was conducted to characterize the responses of selected nitrogen-fixing biocatalysts to various environmental parameters that are likely to be encountered in a scaled-up nitrogen-fixing bioregenerative unit for use in a biologically based life support system (BLSS). The results showed that while both Azolla filiculoides and Azolla nilotica thrived on standard nitrogen-free liquid media, only Azolla filiculoides maintained its growth rate in the presence of 50% by volume of aerobic-bioreactor potato effluent (ABPE) in its liquid medium. The growth rate and Anabaena cavity population of Azolla filiculoides also remained undiminished in the presence of as much as 10 mM of NO3- in its liquid medium. The tolerance of Azolla filiculoides for NO3- however, lay somewhere between 10 and 20 mM of NO3-. Azolla filiculoides failed to grow at 5 mM or greater concentrations of NH4+. The growth rate of the Oscillatoria-dominated microbial mat was significantly elevated by increased silage loading density (16 g/L) as well as by adding 5 mM of NO3- into its liquid medium. Neither the growth rate of Azolla filiculoides nor that of the microbial mat was affected by three levels of photosynthetic photon flux (PPF) (520, 265, and 125 micromoles m-2 s-1) under high-pressure sodium or cool fluorescent lamps.

Anabaena↗
PubMed2002

Water cycles in closed ecological systems: effects of atmospheric pressure.

In bioregenerative life support systems that use plants to generate food and oxygen, the largest mass flux between the plants and their surrounding environment will be water. This water cycle is a consequence of the continuous change of state (evaporation-condensation) from liquid to gas through the process of transpiration and the need to transfer heat (cool) and dehumidify the plant growth chamber. Evapotranspiration rates for full plant canopies can range from ~1 to 10 L m-2 d-1 (~1 to 10 mm m-2 d-1), with the rates depending primarily on the vapor pressure deficit (VPD) between the leaves and the air inside the plant growth chamber. VPD in turn is dependent on the air temperature, leaf temperature, and current value of relative humidity (RH). Concepts for developing closed plant growth systems, such as greenhouses for Mars, have been discussed for many years and the feasibility of such systems will depend on the overall system costs and reliability. One approach for reducing system costs would be to reduce the operating pressure within the greenhouse to reduce structural mass and gas leakage. But managing plant growth environments at low pressures (e.g., controlling humidity and heat exchange) may be difficult, and the effects of low-pressure environments on plant growth and system water cycling need further study. We present experimental evidence to show that water saturation pressures in air under isothermal conditions are only slightly affected by total pressure, but the overall water flux from evaporating surfaces can increase as pressure decreases. Mathematical models describing these observations are presented, along with discussion of the importance for considering "water cycles" in closed bioregenerative life support systems.

Atmospheric Pressure↗
PubMed2003

Farming in space: environmental and biophysical concerns.

The colonization of space will depend on our ability to routinely provide for the metabolic needs (oxygen, water, and food) of a crew with minimal re-supply from Earth. On Earth, these functions are facilitated by the cultivation of plant crops, thus it is important to develop plant-based food production systems to sustain the presence of mankind in space. Farming practices on earth have evolved for thousands of years to meet both the demands of an ever-increasing population and the availability of scarce resources, and now these practices must adapt to accommodate the effects of global warming. Similar challenges are expected when earth-based agricultural practices are adapted for space-based agriculture. A key variable in space is gravity; planets (e.g. Mars, 1/3 g) and moons (e.g. Earth's moon, 1/6 g) differ from spacecraft orbiting the Earth (e.g. Space stations) or orbital transfer vehicles that are subject to microgravity. The movement of heat, water vapor, CO2 and O2 between plant surfaces and their environment is also affected by gravity. In microgravity, these processes may also be affected by reduced mass transport and thicker boundary layers around plant organs caused by the absence of buoyancy dependent convective transport. Future space farmers will have to adapt their practices to accommodate microgravity, high and low extremes in ambient temperatures, reduced atmospheric pressures, atmospheres containing high volatile organic carbon contents, and elevated to super-elevated CO2 concentrations. Farming in space must also be carried out within power-, volume-, and mass-limited life support systems and must share resources with manned crews. Improved lighting and sensor technologies will have to be developed and tested for use in space. These developments should also help make crop production in terrestrial controlled environments (plant growth chambers and greenhouses) more efficient and, therefore, make these alternative agricultural systems more economically feasible food production systems.

Agriculture↗
PubMed1997

Integration of crop production with CELSS waste management.

Lettuce plants were grown utilizing water, inorganic elements, and CO2 inputs recovered from waste streams. The impact of these waste-derived inputs on the growth of lettuce was quantified and compared with results obtained when reagent grade inputs were used. Phytotoxicity was evident in both the untreated wastewater stream and the recovered CO2 stream. The toxicity of surfactants in wastewater was removed using several treatment systems. Harmful effects of gaseous products resulting from incineration of inedible biomass on crop growth were observed. No phytotoxicity was observed when inorganic elements recovered from incinerated biomass ash were used to prepare the hydroponic solution, but the balance of nutrients had to be modified to achieve near optimal growth. The results were used to evaluate closure potential of water and inorganic elemental loops for integrated plant growth and human requirements.

Biomass↗
PubMed1997

Significance of rhizosphere microorganisms in reclaiming water in a CELSS.

Plant-microbe interactions, such as those of the rhizosphere, may be ideally suited for recycling water in a Controlled Ecological Life Support System (CELSS). The primary contaminant of waste hygiene water will be surfactants or soaps. We identified changes in the microbial ecology in the rhizosphere of hydroponical1y grown lettuce during exposure to surfactant. Six week old lettuce plants were transferred into a chamber with a recirculating hydroponic system. Microbial density and population composition were determined for the nutrient solution prior to introduction of plants and then again with plants prior to surfactant addition. The surfactant Igepon was added to the recirculating nutrient solution to a final concentration of 1.0 g L-1. Bacteria density and species diversity of the solution were monitored over a 72-h period following introduction of Igepon. Nine distinct bacterial types were identified in the rhisosphere; three species accounted for 87% of the normal rhizosphere population. Microbial cell number increased in the presence of Igepon, however species diversity declined. At the point when Igepon was degraded from solution, diversity was reduced to only two species. Igepon was found to be degraded directly by only one species found in the rhizosphere. Since surfactants are degraded from the waste hygiene water within 24 h, the potential for using rhizosphere bacteria as a waste processor in a CELSS is promising.

Biodegradation, Environmental↗
PubMed1997

Recycling of inorganic nutrients for hydroponic crop production following incineration of inedible biomass.

The goal of resource recovery in a regenerative life support system is maintenance of product quality to sure support of reliable and predictable levels of life support function performance by the crop plant component. Further, these systems must be maintained over extended periods of time, requiring maintenance of nutrient solutions to avoid toxicity and deficiencies. The focus of this study was to determine the suitability of the ash product following incineration of inedible biomass as a source of inorganic nutrients for hydroponic crop production. Inedible wheat biomass was incinerated and ash quality characterized. The incinerator ash was dissolved in adequate nitric acid to establish a consistent nitrogen concentration is all nutrient solution treatments. Four experimental nutrient treatments were included: control, ash only, ash supplemented to match the control treatment, and ash only quality formulated with reagent grade chemicals. When nutrient solutions were formulated using only ash following incineration of inedible biomass, a balance in solution is established representing elemental retention following incineration and nutrient proportions present in the original biomass. The resulting solution is not identical to the control. This imbalance resulted in a suppression of crop growth. When the ash is supplemented with reagent grade chemicals to establish the same balance as in the control--growth is identical to the control. The ash appears to carry no phytotoxic materials. Growth in solution formulated with reagent grade chemicals but matching the quality of the ash only treatment resulted in similar growth to that of the ash only treatment. The ash product resulting from incineration of inedible biomass appears to be a suitable form for recycle of inorganic nutrients to crop production.

Biomass↗
PubMed2002

NASA food systems: past, present, and future.

The development of space food has been evolving since the Soviet cosmonaut, German Titov, became the first human to eat in space in August 1961. John Glenn was the first American to consume food, applesauce, on the third manned Mercury mission in August 1962. Before these events, there was no knowledge that humans would be able to swallow and, hence, eat in weightlessness. Space food development began with highly engineered foods that met rigid requirements imposed by spacecraft design and short mission durations. Improvements in the habitability of the spacecraft have permitted improvements in the quality of space food. As the missions became longer, the need for better nutrition, more variety, and easily consumable foods also became more important. Currently, the International Space Station astronauts have a wide variety of foods. The goal is to provide acceptable foods that taste similar to foods we eat here on Earth. Extended planetary stays will require even more variety and more technologic advances. Plants will be grown to recycle the air and water and will provide food for the crew. These harvested crops will need to be processed into safe, healthy, and acceptable food ingredients that can then be prepared into menu items.

Eating↗
PubMed2005

Simulation of gaseous diffusion in partially saturated porous media under variable gravity with lattice Boltzmann methods.

Liquid distributions in unsaturated porous media under different gravitational accelerations and corresponding macroscopic gaseous diffusion coefficients were investigated to enhance understanding of plant growth conditions in microgravity. We used a single-component, multiphase lattice Boltzmann code to simulate liquid configurations in two-dimensional porous media at varying water contents for different gravity conditions and measured gas diffusion through the media using a multicomponent lattice Boltzmann code. The relative diffusion coefficients (D rel) for simulations with and without gravity as functions of air-filled porosity were in good agreement with measured data and established models. We found significant differences in liquid configuration in porous media, leading to reductions in D rel of up to 25% under zero gravity. The study highlights potential applications of the lattice Boltzmann method for rapid and cost-effective evaluation of alternative plant growth media designs under variable gravity.

Computer Simulation↗
PubMed2003

The effect of drying and size reduction pretreatments on recovery of inorganic crop nutrients from inedible wheat residues.

Inorganic nutrients can be easily recovered from ALS crop residue solid wastes by aqueous leaching. However, oven drying and milling pretreatment of these residues has been frequently required to accommodate crop scientists and facility storage limitations. As part of a research study that will compare three different bioreactor technologies for processing these wastes, we realized that different drying and size-reduction pretreatments had been utilized for each technology. This paper compares the effects of residue pretreatment on recovery of nutrients by leaching. Pretreatments included three drying methods [fresh, oven-dried (70 degrees C overnight), and freeze-dried] and two size reduction methods [chopped (2 cm length) and milled (2 mm diameter)]. Determination of mass balances (dry weight and ash content of solids) before and after leaching indicated solubilization was least for fresh residues (23% dry weight loss and 50% for ash loss), and most for freeze-dried residues (41-47% dry weight loss and nearly 100% for ash loss). Mineral recovery of major elements (NO3, PO4, K, Ca, and Mg) in leachates was poorest for fresh residues. P and K recovery in leachates were best for oven-dried residues and Ca, Mg, and N recovery best for freeze-dried residues. The differences in recovery for N, P, and K in leachates were minimal between chopping and milling and slightly better for Ca and Mg from milled residues.

Biomass↗
PubMed2004

Water cycle and its management for plant habitats at reduced pressures.

Experimental and mathematical models were developed for describing and testing temperature and humidity parameters for plant production in bioregenerative life support systems. A factor was included for analyzing systems operating at low (10-101.3 kPa) pressure to reduce gas leakage and structural mass (e.g., inflatable greenhouses for space application). The expected close relationship between temperature and relative humidity was observed, along with the importance of heat exchanger coil temperature and air circulation rate. The presence of plants in closed habitats results in increased water flux through the system. Changes in pressure affect gas diffusion rates and surface boundary layers, and change convective transfer capabilities and water evaporation rates. A consistent observation from studies with plants at reduced pressures is increased evapotranspiration rates, even at constant vapor pressure deficits. This suggests that plant water status is a critical factor for managing low-pressure production systems. The approach suggested should help space mission planners design artificial environments in closed habitats.

Atmospheric Pressure↗
PubMed2001

Electrolytic removal of nitrate from crop residues.

The Controlled Ecological Life Support System (CELSS) resource recovery system, which is a waste-processing system,uses aerobic and anaerobic bioreactors to recover plants nutrients and secondary foods from the inedible biomass. Crop residues contain a significant amount of nitrate. There are actually two major problems concerning nitrate: 1) both CELSS biomass production and resource recovery consume large quantities of nitric acid, and 2) nitrate causes a variety of problems in both aerobic and anaerobic bioreactors. The nitrate anion causes several problems in the resource recovery system in such a way that removal prior to the process is highly desirable. The technique proposed to remove nitrate from potato inedible biomass leachate and to satisfy the nitric acid demand was a four-compartment electrolytic cell. In order to establish the electrolytic cell performance variables, experiments were carried out using potato crop residue aqueous leachate as the diluate solution. The variables studied were the potato biomass leachate composition and electrical properties, preparation of compartment solutions to be compatible with the electrolytic system, limiting current density, nutrients removal rates as a function of current density, fluid hydrodynamic conditions, applied voltage, and process operating time during batch recirculation operation. Results indicated that the limiting current density (maximum operating current density) was directly proportional to the solution electrical conductivity an a power function of the linear fluid velocity in the range between 0.083 and 0.403 m/s. During the electrolytic cell once-through operation, the nitrate, potassium, and other nutrient removal rates were proportional to the current density and were inversely proportional to fluid velocity. The removal of monovalent ions was found to be higher than divalent ones. Under batch recirculation operation at constant applied voltage of 4.5 and 8.5 V, it was found that the nutrient removal rates were independent of applied voltage, but were proportional to the ions concentration and operating time.

Anions↗
PubMed2004

Influence of nitrogen nutrition management on biomass partitioning and nitrogen use efficiency indices in hydroponically grown potato.

The National Aeronautics and Space Administration (NASA) has been conducting controlled environment research with potatoes (Solanum tuberosum L.) in recirculating nutrient film technique (NFT)-hydroponic systems as a human life support component during long-duration spaceflight. Standard nutrient solution management approaches include constant pH regulation with nitric acid (HNO3) and daily adjustment of electrical conductivity (EC) equivalent to half-strength modified Hoagland's solution, where nitrate (NO3-) is the sole nitrogen (N) source. Although tuber yields have been excellent with such an approach, N use efficiency indices are expected to be low relative to tuber biomass production. Furthermore, the high amount of N used in NFT-hydroponics, typically results in high inedible biomass, which conflicts with the need to minimize system mass, volume, and expenditure of resources for long-duration missions. More effective strategies of N fertilization need to be developed to more closely match N supply with demand of the crop. Hence, the primary objective of this study was to identify the optimal N management regime and plant N requirement to achieve high yields and to avoid inefficient use of N and excess inedible biomass production. In separate 84-day cropping experiments, three N management protocols were tested. Treatments which decreased NO3(-)-N supply indirectly through lowering nutrient solution EC (Expt. I), or disabling pH control, and/or supplying NH4(+)-N (Expt. III) did not significantly benefit tuber yield, but did influence N use efficiency indices. When supplied with an external 7.5 mM NO3(-)-N for the first 42 days after planting (DAP), lowered to 1.0 mM NO3(-)-N during the final 42 days (Expt. II), plants were able to achieve yields on par with plants which received constant 7.5 mM NO3(-)-N (control). By abruptly decreasing N supply at tuber initiation in Expt. II, less N was taken up and accumulated by plants compared to those which received high constant N (control). However, proportionately more plant accumulated N was used (N use efficiency) to produce tuber biomass when N supply was abruptly lowered at tuber initiation in Expt. II. Hence, a hydroponic nutrient solution N management system may be modified to elicit greater plant N-use while maintaining overall high tuber yield as opposed to achieving high tuber yields through excess N supply and shoot growth.

Biomass↗
PubMed1999

Adsorption processes in spacecraft environmental control and life support systems.

The environmental control and life support system on a spacecraft maintains a safe and comfortable environment in which the crew can live and work by supplying oxygen and water and by removing carbon dioxide, water vapor, and trace contaminants from cabin air. Although open-loop systems have been used successfully in the past for short-duration missions, the economics of current and future long-duration missions in space will make nearly complete recycling of air and water imperative. A variety of operations will be necessary to achieve the goal of nearly complete recycling. These include separation and reduction of carbon dioxide, removal of trace gas-phase contaminants, recovery and purification of humidity condensate, purification and polishing of wastewater streams, and others. Several of these can be performed totally or in part by adsorption processes. These processes are good candidates to perform separations and purifications in space due to their gravity independence, high reliability, relative high energy efficiency, design flexibility, technological maturity, and regenerative nature. For these reasons, adsorption has historically played a key role in life support on U.S. and Russian piloted spacecraft. Among the life support applications that can be achieved through use of adsorption technology are removal of trace contaminants and carbon dioxide from cabin air and recovery of potable water from waste streams. In each of these cases adsorption technology has been selected for use onboard the International Space Station. The requirements, science, and hardware for these applications are discussed. Human space exploration may eventually lead to construction of planetary habitats. These habitats may provide additional opportunities for use of adsorption processes, such as control of greenhouse gas composition, and may have different resources available to them, such as gases present in the planetary atmosphere. Separation and purification processes based on adsorption can be expected to continue to fulfill environmental control and life support needs on future missions.

Adsorption↗
PubMed2003

Life support approaches for Mars missions.

Life support approaches for Mars missions are evaluated using an equivalent system mass (ESM) approach, in which all significant costs are converted into mass units. The best approach, as defined by the lowest mission ESM, depends on several mission parameters, notably duration, environment and consequent infrastructure costs, and crew size, as well as the characteristics of the technologies which are available. Generally, for the missions under consideration, physicochemical regeneration is most cost effective. However, bioregeneration is likely to be of use for producing salad crops for any mission, for producing staple crops for medium duration missions, and for most food, air and water regeneration for long missions (durations of a decade). Potential applications of in situ resource utilization need to be considered further.

Biodegradation, Environmental↗
PubMed2003

Waste system implications for Mars missions.

Waste technologies for Mars missions have been analyzed, considering equivalent system mass and interface loads. Storage or dumping seems most appropriate for early missions with low food closure. Composting or other treatment of inedible biomass in a bioreactor seems most attractive for moderate food closure (50-75%). Some form of physicochemical oxidation of the composted residue might be needed for increased food closure, but oxidation of all waste does not seem appropriate due to excess of production of carbon dioxide over demand. More comprehensive analysis considering interfaces with other mission systems is needed. In particular, in-situ resource utilization is not considered, and might provide resources more cheaply than waste processing.

Biodegradation, Environmental↗
PubMed1997

Computer modeling for advanced life support system analysis.

This article discusses the equivalent mass approach to advanced life support system analysis, describes a computer model developed to use this approach, and presents early results from modeling the NASA JSC BioPlex. The model is built using an object oriented approach and G2, a commercially available modeling package Cost factor equivalencies are given for the Volosin scenarios. Plant data from NASA KSC and Utah State University (USU) are used, together with configuration data from the BioPlex design effort. Initial results focus on the importance of obtaining high plant productivity with a flight-like configuration.

Atmosphere↗
PubMed1998

Bioregenerative [correction of bioregnerative] life support: not a picnic.

If humans are to live permanently in space, regenerative life support systems are an enabling technology and must replace the picnic approach of taking all supplies required for each mission. These systems are classified by technologies as either physical/chemical or bioregenerative. Both of these system-types can recycle water, remove carbon dioxide, produce oxygen, and recover essential elements from waste products. Bioregenerative can also produce food, thus, making it essential if humans are to exist in space independent of earth. A solely bioregenerative life support system includes plants as a biomass production module and microbial organisms in bioreactors as a resource recovery module. In the Advanced Life Support Program, bioregenerative life support systems are being investigated through a research and technology development project which includes large scale testing as part of the Breadboard Project and human tests conducted in the soon to be constructed BioPlex facility. Research and technology development efforts are directed toward optimizing biomass productivity in controlled chambers by developing light weight, energy efficient, and automated systems; recycling liquid and solid wastes; baselining the operation of bioreactors; determining system microbial stability; assessing chemical contamination; and building models required for long term system operations. The program will include space flight studies in the near future to determine if these life support technologies will function in microgravity. When a bioregenerative system is finally incorporated into a mission, the conversion from a picnic and resupply mentality to permanent recycling and independence from earth will be complete.

Biofilms↗