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.
Bench top scale bioreactors investigated the effects of different operating conditions, determined reactor-to-reactor variability, and validated the computer models. A Taguchi statistical approach was utilized to investigate the effect of feed pH, air/fluid mixing, and hydraulic retention time (HRT) on the performance of three identical bioreactors. Changes in feed pH, between low and high levels, showed no significant effect on performance. In contrast, higher air/fluid mixing and HRT increased the rate of Total Organic Carbon (TOC) degradation. Operating under identical conditions, all three reactors demonstrated similar performance over a six month period, indicating that there is little internal variability between reactors. Throughout the experiment all three bioreactors maintained TOC degradation of 85 percent or better.
The purpose of this paper is to describe the initial development of the detailed bioreactor model and its supporting experimental investigations.