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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.

Activated sludge waste water processing is one of the most common technologies used in municipal waste water treatment facilities. Bioregenerative waste water treatment research at the NASA Johnson Space Center has, however, focused on the use of attached growth bioreactors due to their advantageous solids retention capability. The development of cross flow filtration methodologies in recent years has provided a means for significantly increasing solids retention time of activated sludge reactors. The settling tank traditionally used in municipal activated sludge processes for biomass retention is replaced with a microgravity compatible cross-flow biomass filter. The resulting activated sludge reactor has entirely independent solids and hydraulic retention times that may be modified as necessary to enhance processing performance. This paper describes the development of such an activated sludge bioreactor and the performance characteristics achieved to date.

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.

A mathematical model of a fixed-film biological waste water processor has been developed for system level simulations of the Trickle Filter Bioreactor (TPB) currently operating at the NASA Johnson Space Center (JSC Hybrid Regenerative Water Recovery System (HRWRS) laboratory. The TFB model has been compared against HRWRS lab data as well as an independently developed mathematical model of a waste water processing biofilm. On a microscopic level, the fundamental equations which describe the simultaneous diffusion and reaction within the biofilm are simplified by use of polynomial substitution to provide a solution which can be solved much more rapidly than traditional finite difference solution methods. Phenomenological transport equations are used to couple the biofilm and liquid phases as well as the gas and liquid phases.

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.

The NASA Johnson Space Center has plans to integrate a Solid Amine Water Desorbed (SAWD II) carbon dioxide removal subsystem into the Variable Pressure Growth Chamber (VPGC). The SAWD II subsystem will be used to remove any excess carbon dioxide (CO2) input into the VPGC which is not assimilated by the plants growing in the chamber. An analysis of the integrated VPGC-SAWD II system was performed using a mathematical model of the system implemented in the Computer-Aided System Engineering and Analysis (CASE/A) package. The analysis consisted of an evaluation of the SAWD II subsystem configuration within the VPGC, the planned operations for the subsystem, and the overall performance of the subsystem and other VPGC subsystems. Based on the model runs, recommendations were made concerning the SAWD II subsystem configuration and operations, and the chambers' automatic CO2 injection control subsystem.

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 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.

A computer simulation of the variable pressure growth chamber (VPGC) located at the NASA Johnson Space Center (JSC) has been developed using an expanded version of the Computer-Aided Systems Engineering and Analysis (CASE/A) simulation package. The VPGC is a pressure chamber that has been outfitted to support the growth of approximately 10.6 m2 of plants in an enclosed environment of approximately 27 m3 (Reference 1). CASE/A is a physical/chemical system-level simulation package originally developed to model the life support systems of Space Station Freedom. The expanded version of CASE/A extends the simulation package by including biological components, primarily plant growth algorithms. The configuration, modeling methods and verification of the CASE/A Variable Pressure Growth Chamber model are described. Performance estimates generated from the model are compared to data from recent lettuce growth experiments in the VPGC.

A computer simulation of the Variable Pressure Growth Chamber (VPGC), located at the NASA Johnson Space Center, has been developed using the Computer Aided Systems Engineering and Analysis (CASE/A) package. The model has been used to perform several analyses of the VPGC. The analyses consisted of a study of the effects of a human metabolic load on the VPGC and a study of two new configurations for the temperature and humidity control (THC) subsystem in the VPGC. The objective of the human load analysis was to study the effects of a human metabolic load on the air revitalization and THC subsystems. This included the effects on the quantity of carbon dioxide injected and oxygen removed from the chamber and the effects of the additional sensible and latent heat loads. The objective of the configuration analysis was to compare the two new THC configurations against the current THC configuration to determine which had the best performance.