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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.

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.

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.

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.

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.