Modeling Spatially Variant Processes in Plug-Flow-Like Activated Sludge Reactors
Publication: Journal of Environmental Engineering
Volume 142, Issue 6
Abstract
The nonideal segregated flow (SF) model was adapted for modeling single-sludge carbonaceous biochemical oxygen demand (cBOD) reduction and nitrification within a plug-flow-like bioreactor. Principles associated with the CMFRs (complete-mix flow reactors) in series (also called continuous-flow stirred tank reactors, CFSTRs, in series, or simply tanks in series, TiS) and plug-flow with dispersion (PFD) models were combined with the SF model to develop a powerful modeling approach with the capability to predict reactant and product concentrations and process rates as a function of position along the reactor flow path. The single CMFR, plug-flow (PF), TiS, and SF models were then used to simulate the steady-state performance of a hypothetical activated sludge bioreactor to compare capabilities to predict spatial process variation. All simulations were forced to a common target effluent ammonia-nitrogen concentration, yielding unique sets of predicted performance parameters from each of the models. Predictions of positional oxygen consumption rates were generated and compared to discern model applicability. The SF model was shown to be quite adaptable to modeling of spatially variant processes in plug-flow-like reactors with predictions highly sensitive to the magnitude of the dispersion coefficient employed to characterize reactor hydrodynamics. Key limitations of the currently developed modeling approach include (1) to-date development is for steady state conditions, (2) the bioreactor is decoupled from sedimentation operations, and (3) the model is not yet calibrated against actual lab-scale or full-scale reactor systems.
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Acknowledgments
The author acknowledges the work of Zane Anthony Green, a MS student at the SD School of Mines and Technology when work on this topic was initiated. Zane’s unfunded thesis work did not gain the final solution. However, his enthusiasm for and willingness to explore nonideal reactor theory and principles were critical in setting this effort on the path leading to the eventual successful application of segregated flow principles to modeling spatially-variant processes operative in plug-flow-like activated sludge reactors.
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Published In
Journal of Environmental Engineering
Volume 142 • Issue 6 • June 2016
Copyright
© 2016 American Society of Civil Engineers.
History
Received: Mar 1, 2015
Accepted: Nov 2, 2015
Published online: Feb 4, 2016
Published in print: Jun 1, 2016
Discussion open until: Jul 4, 2016
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