Effects of Substrate Flow Regime on Bacterial Dynamics in a Continuous Stirred Tank Reactor (CSTR)
This project centered around a previous experiment involving membrane bioreactors (MBR). The primary objective was to determine the effects of varying flow regime of influent substrate to bacterial communities. Past studies showed that a significant variation with respect to bacterial dynamics was exhibited when substrate flow was changed from pulse to continuous input. While it is not known if this operational change was solely responsible for the physiological shift in bacterial attachment, studies were setup to determine if significant deviation was present between the two flow regimes.
Background
• Advanced Life Support (ALS) water recovery systems regenerate dirty water to remove organic and nitrogen compounds filtered into a more usable effluent (2)
• An MBR is used for the treatment of space-generated waste streams
• Combines suspended-growth reactors with the capability of solids separation using membrane technology
• Amount of wastewater processed is increased due to the membranes allow for a high biomass concentration within the reactor
• Slow-growing microbes and faster-growing bacteria are able to grow in the same bioreactor due to long solid retention times (STR)
• In a recent MBR study it was observed that a variation in bacterial dynamics was exhibited when the feed regime was changed from pulse to continuous (see chart below).
Above: Schematic of Chemostat process to evaluate flow regime and the affects associated on bacterial dynamics
Study Setup and Objectives
4-CSTR reactors were used with a stir-bar for fluidization. A nutrient-rich feed solution and an air stream also were provided.
Evaluate effects of different feed regimes as well as determine specific substrate utilization rates and evaluate differences in microbial dynamics due to feed variation.
Conclusions
• From the analysis, a lag of cells is seen in the pulse fed reactors. This may not indicate significant deviation from continuous fed reactors.
• Visual analysis of the reactors showed a larger accumulation of wall growth in the pulse fed reactors.
• In a previous MBR study (2), attached biofilm was present at the time of the modified flow regime. This could not be duplicated in this study due to the required time to develop a steady biofilm prior to the experiment. This may have led to significant changes in the operation and the bacterial dynamics of the reactor systems.
References
1) Garland J, Hummerick M, Levine L, Roberts M, Strayer R. (2003) Integrated Evaluation of Submerged Membrane Bioreactor Technology: Phase II –Nitrification Establishment. NASA. TDP. Year 2 Final Report.
2) Kortenkamp D, Bell S. (2003) Simulating Advanced Life Support Systems for Integrated Controls Research. SAE International. Paper # 2003-01-2546.
3) Rittman, B .E, McCarty, P. L. (2001) Environmental Biotechnology: Principles and Applications. McGraw Hill Inc, New York.
Author: Elinor Davis, SLSTP 2004, University of Wyoming, Laramie, WY
Principal Investigator: Tony Rector, Dynamac Corporation
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