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Technologies for the recycling of water are a primary goal of NASA’s advanced life support programs. Biological processes have been identified as an attractive method for wastewater processing. A fundamental new bioreactor based on a traditional activated sludge process is demonstrated that treats hygiene wastewater using magnetic iron oxide particles agglomerated with microbial cells. In this bioreactor, microbes are suspended in magnetic flocs in a wastewater medium. Instead of a traditional gravity separator used in activated sludge operations, a magnetic separator removes the microbial flocs from the outlet stream. The reactor separation operates continuously, independent of gravitational influences. The reactor has been able to simultaneously remove 98% of high levels of both nitrogenous and organic carbon impurities from the wastewater as well as achieve acceptably low levels of total suspended solids.

Long duration manned space missions will require integrated biological and physicochemical processes for recovery of resources from wastes. This paper discusses a hybrid regenerative biological and physicochemical water recovery system designed and built at NASA's Crew and Thermal Systems Division (CTSD) at Johnson Space Center (JSC). The system is sized for a four-person crew and consists of a two-stage, aerobic, trickling filter bioreactor; a reverse osmosis system; and a photocatalytic oxidation system. The system was designed to accommodate high organic and inorganic loadings and a low hydraulic loading. The bioreactor was designed to oxidize organics to carbon dioxide and water; the reverse osmosis system reduces inorganic content to potable quality; and the photocatalytic oxidation unit removes residual organic impurities (part per million range) and provides in-situ disinfection. The design and performance of the hybrid system for producing potable/hygiene water is described.

Bioreactor technology for waste water reclamation in a regenerative life support system (RLSS) is currently being developed by a team of NASA and major aerospace companies. To advance this technology, several activities are being performed concurrently; these include conducting small-scale studies and developing computer models. Small-scale studies are being performed to characterize and enhance the bioprocesses occurring within the bioreactor. New bioreactor configurations have been investigated which improved total organic carbon degradation as well as nitrification, the polishing step which converts nitrogenous wastes into forms that are easily removable from the water. Small-scale studies have also been performed using an activated sludge reactor demonstrating that TOC reduction and nitrification can occur in a single reactor. Computer models have been developed to guide the laboratory studies and to assist in full-scale system design.

Bioreactor technology is currently being developed by a team of NASA and major aerospace companies to provide capabilities for water reclamation within a Regenerative Life Support System (RLSS). An integrated approach is being used for this development process consisting of fundamental laboratory studies, full-scale experimental studies and mathematical modeling. The laboratory studies are focused on a series of identical bioreactors which are being used to develop an understanding of the kinetics, growth characteristics, and viability of the microbial population in the reactors through variation of key parameters. These studies have provided insight into system control issues, development of advanced reactor design concepts, and establishment of key parameter values for the mathematical modeling effort. The full-scale experimental studies are being used to develop a complete water reclamation system founded on a biologically-based primary water processor.

Development of bioreactor technology for a regenerative life support primary water processor is ongoing by a team, composed of NASA and major aerospace companies, using a concurrent integrated approach. This approach consists of performing small-scale reactor experimental investigations, large-scale experimental studies, and computer modeling efforts on both the bioprocessor subsystem level and on the integrated water recovery system level. Bench-top experimental studies are aimed at developing an understanding of the biological process and the effect of key parameters on the process, determining the operational envelope for the regenerative life support application, and addressing process control issues. The large-scale experimental studies, in which a bioprocessor is one subsystem of an overall water recovery system, address the full-scale system integration and operational issues.

The Lunar Mars Life Support Test Project (LMLSTP) Phase III test was the final test in a series of tests conducted to evaluate regenerative life support systems performance over increasingly longer durations. The Phase III test broke new ground for the U.S. Space Program by being the first test to look at integration of biological and physical-chemical systems for air, water and solid waste recovery for a crew of four for 91 days. Microbial bioreactors were used as the first step in the water recovery system (WRS). This biologically based WRS continuously recovered 100% of the water used by the crew consistent with NASA's strict potable standards. The air revitalization system was a combination of physical-chemical hardware and wheat plants which worked together to remove and reduce the crew's metabolically produced carbon dioxide and provide oxygen.

Computer models are currently being developed by NASA and major aerospace companies to characterize regenerative life support waste water reclamation bioreactors. Detailed models increase understanding of complex processes within the bioreactors and predict performance capabilities over a wide range of operating parameters. Bench-top scale bioreactors are contributing to the development and validation of these models. The purpose of the detailed bioreactor model is to simulate the complex water purification processes as accurately as possible by minimizing the use of simplifying assumptions and empirical relationships. Fundamental equations of mass transport and microbial kinetics were implemented in a finite-difference model structure to maximize accuracy and adaptability to various bioreactor configurations. The model development is based upon concepts and data from the available literature and data from the bench top bioreactor investigations.

The Early Human Testing Initiative (EHTI) Phase I Human Test, performed by the Crew and Thermal Systems Division at Johnson Space Center, demonstrated the ability of a crop of wheat to provide air revitalization for a human test subject for a 15-day period. The test demonstrated three different methods for control of oxygen and carbon dioxide concentrations for the human/plant system and obtained data on trace contaminants generated by both the human and plants during the test and their effects on each other. The crop was planted in the Variable Pressure Growth Chamber (VPGC) on July 24, 1995 and the test subject entered the adjoining airlock on day 17 of the wheat's growth cycle. The test subject stayed in the chamber for a total of 15 days, 1 hour and 20 minutes. Air was mixed between the plant chamber and airlock to provide oxygen to the test subject and carbon dioxide to the plants by an interchamber ventilation system.

The design and operation of hybrid physical/chemical and biological life support systems for space application is a complex and difficult process. This paper describes the approach and results of an effort to characterize wheat growth, under various environmental conditions, at the Johnson Space Center's (JSC) Ambient Pressure Growth Chamber (APGC). Using a designed experiment, a test plan was developed for varying environmental parameters during a wheat growth experiment. The test plan was developed using a Central Composite approach to experimental design. As a result of the experimental runs, an empirical model of both the transpiration process and carbon dioxide assimilation for wheat growth over specified ranges of environmental parameters has been developed. The environmental parameters include carbon dioxide concentration, ambient chamber temperature, vapor pressure deficit, and air velocity.

Reclamation of purified water from waste water will be a necessity for self-sufficiency on Lunar and Martian outposts. Biological waste water treatment is advantageous because it has low temperature, low pressure, and low power requirements. Four different media were tested for use as biological growth substrates in bench-top aerobic trickling filter bioreactors in the Hybrid Regenerative Water Recovery Lab at Johnson Space Center. The four media tested included a mixture of open skeleton polypropylene spheres and cylinders, ceramic berl saddles, solid glass beads, and small rocks. The media were tested to characterize the organism inoculation rate; the steady state performance; the response to system upsets; and the column characteristics like flooding and channeling. Results indicate that the ceramic berl saddles performed best with respect to inoculation rate, steady state performance, and response to system upsets.

An 84 day wheat crop was grown in the Variable Pressure Growth Chamber (VPGC) at Johnson Space Center (JSC). The VPGC is an atmospherically closed, controlled environment facility used to evaluate the use of higher plants as part of a regenerative life support system. The chamber has 10.6 m2 of growing area consisting of 480 pots of calcined clay support media. The chamber is lit by very high output, cool white fluorescent bulbs. Five wheat seeds were planted per pot giving a seeding density of 227 seeds·m-2. Pots were irrigated with a modified half strength Hoagland's nutrient solution three or six times per day depending on the crop age. At the plant canopy, the average temperature during the test was 22 ° C, relative humidity was maintained at 69%, CO2 concentration was 1000 ppm, photoperiod was continuous light, and the light intensity averaged 350 μmol·m-2·s-1.

An integrated water recovery system was operated for 91 days in support of the Lunar Mars Life Support Test Project (LMLSTP) Phase III test. The system combined both biological and physical-chemical processes to treat a combined wastewater stream consisting of waste hygiene water, urine, and humidity condensate. Biological processes were used for primary degradation of organic material as well as for nitrification of ammonium in the wastewater. Physical-chemical systems removed inorganic salts from the water and provided post-treatment. The integrated system provided potable water to the crew throughout the test. This paper describes the water recovery system and reviews the performance of the system during the test.

The development of regenerative life support systems (RLSS) to support long duration manned space exploration is of great importance. To design future chambers effectively, it is necessary to model both chamber performance and plant growth in current systems. The Johnson Space Center RLSS test bed, which consists of the Variable Pressure Growth Chamber (VPGC) and the Ambient Pressure Growth Chamber (APGC), is a facility that is being used to investigate plant growth and support hardware integration. Detailed and simplified models of the VPGC and APGC have been developed to investigate system performance and response to changes in loading as well as to study long-term plant growth under varying environmental conditions, including temperature, light level, CO2 level, dew point or relative humidity, and photoperiod. To support these studies, models of two crops, lettuce and wheat, have also been developed and integrated into the detailed and simplified simulations of each chamber.

The TIMES system was evaluated to determine its ability to process reverse osmosis (RO) brine as one of the Advanced Water Processor steps. Since preliminary testing performed in 1998 showed that the membrane typically used in the process (Nafion 117) offered a very poor ammonia rejection, a search for an alternate membrane exhibiting high ammonia rejection capability was initiated under NASA-JSC funding. This investigation has resulted in the selection of a PolyVinylAlcohol (PVA) composite membrane as a replacement. When processing RO brine and untreated human urine as feeds, the Pervap 2201 membrane showed a 96% ammonia rejection over a large range of ammonia concentration. The water permeation rates in both laboratory-scale and pilot scale testings were also similar to the Nafion. The water permeance of the Pervap 2201 was approximately 7.5 kg/h/m2/atm (1.1 lb/h/m2/psi).

A canopy of plants may become a vital component of advanced controlled ecological life support systems (CELSS). The interactions of the canopy with its environment need to be modeled so that designers can properly assess alternate configurations and operating strategies. Collective behavior of an entire canopy can sometimes be more expeditiously modeled than microscopic processes while preserving the robustness of the model for analysis of a CELSS. Water transpiration is a particularly important canopy process for which it is possible to link underlying microscopic processes and arrive at a description of canopy-level aggregated behavior. The underlying fundamental processes driving transpiration are relatively well understood. Unfortunately, the usual characterization of transpiration relies on parameters such as stomatal and boundary layer conductivities that are not directly measurable in typical CELSS designs.

Two crops of lettuce (Lactuca sativa cv. Waldmann's Green) were grown in the Regenerative Life Support Systems (RLSS) Test Bed at NASA's Johnson Space Center. The RLSS Test Bed is an atmospherically closed, controlled environment facility for the evaluation of regenerative life support systems using higher plants. The chamber encloses 10.6 m2 of growth area under cool-white fluorescent lamps. Lettuce was double seeded in 480 pots, each containing about 250 cm3 of calcined-clay substrate. Each pot was irrigated with half-strength Hoagland's nutrient solution at an average total applied amount of 2.5 and 1.8 liters pot-1, respectively, over each of the two 30-day crop tests. Average environmental and cultural conditions during both tests were 23°C air temperature, 72% relative humidity, 1000 ppm carbon dioxide (CO2), 16h light/8h dark photoperiod, and 356 μmol m-2s-1 photosynthetic photon flux.

Biological wastewater processing has been under investigation by AlliedSignal Aerospace and NASA Johnson Space Center (JSC) for future use in space. Testing at JSC in the Hybrid Regenerative Water Recovery System (HRWRS) in preparation for future closed human testing has been performed. Computer models have been developed to aid in the design of a new four-person immobilized cell bioreactor. The design of the reactor and validation of the computer model is presented. In addition, the total organic carbon (TOC) computer model has been expanded to begin investigation of nitrification. This model is being developed to identify the key parameters of the nitrification process, and to improve the design and operating conditions of nitrifying bioreactors. In addition, the model can be used as a design tool to rapidly predict the effects of changes in operational conditions and reactor design, significantly reducing the number and duration of experiments required.

As part of its integrated system test bed capability, NASA's Advanced Life Support Program has undertaken the development of a large-scale advanced life support facility capable of supporting long-duration testing of integrated, regenerative biological and physicochemical life support systems. This facility--the Advanced Life Support Human-Rated Test Facility (HRTF) is currently being built at the Johnson Space Center. The HRTF is comprised of a series of interconnected chambers with a sealed internal environment capable of supporting a test crew of four for periods exceeding one year. The life support system will consist of both biological and physicochemical components and will perform air revitalization, water recovery, food production, solid waste processing, thermal management, and integrated command and control functions. Currently, a portion of this multichamber facility has been constructed and is being outfitted with basic utilities and infrastructure.