Impacts of Flow and Tracer Release Unsteadiness on Tracer Analysis of Water and Wastewater Treatment Facilities
Publication: Journal of Hydraulic Engineering
Volume 145, Issue 4
Abstract
Computational fluid dynamics (CFD) was used to investigate how residence time analysis based on passive tracer transport in environmental and chemical engineering fluid systems can be significantly affected by flow or tracer release unsteadiness. The unsteadiness may be caused by intermittent influent flow, time-varying operations, and nonuniform tracer release profiles. Oftentimes these unsteady conditions are considered negligible and their impact on residence time analysis is not considered. Systems analyzed included a full-scale stabilization pond, a full-scale oxidation ditch, and full-scale and lab-scale baffled tanks. In the case of the stabilization pond, it was found that time-dependent inflow based on realistic water consumption pattern does not significantly affect mean residence time (MRT) but does have a nonnegligible effect on baffling factor relative to constant inflow. In the case of a surface aerated oxidation ditch, aerator speed was found to have a nonnegligible impact on MRT, and thus it is recommended that CFD tracer studies should consider changes in aerator speed during daily cycles of operation. The slug and step methods were considered for tracer analysis in baffled contactors. It was found that the tracer release time in the slug method should be kept at less than 5% of the theoretical residence time in order to obtain accurate measurements of residence time characteristics. Furthermore, residence time distribution obtained from tracer analysis based on the step method can be affected by the initial transient and subsequent fluctuations in the time series of injected tracer concentration that often characterizes physical experiments.
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Acknowledgments
The authors acknowledge the use of the services provided by Research Computing at the University of South Florida. This work also used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562. K. Pierre acknowledges the Florida Education Fund—McKnight Doctoral Fellowship and the Alfred P. Sloan Foundation for financial support. The authors acknowledge the Bachman Water Treatment Plant and the Hillsborough County Public Utilities for their support this work.
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Published In
Journal of Hydraulic Engineering
Volume 145 • Issue 4 • April 2019
Copyright
©2019 American Society of Civil Engineers.
History
Received: Apr 25, 2018
Accepted: Sep 5, 2018
Published online: Jan 18, 2019
Published in print: Apr 1, 2019
Discussion open until: Jun 18, 2019
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