Online Control of Magnesium Hydroxide Dosing for Sulfide Mitigation in Sewers: Algorithm Development, Simulation Analysis, and Field Validation
Publication: Journal of Environmental Engineering
Volume 142, Issue 12
Abstract
Magnesium hydroxide is a commonly used chemical for controlling corrosion and odor problems in sewers by reducing the transfer of hydrogen sulfide from the liquid to the gas phase through pH elevation. The effectiveness of many current dosing practices is unsatisfactory due to negligence of the dynamics of sewage flow and characteristics, and their effects on sewage pH. This paper reports the design and validation of the first online control algorithm for dosing to sewers. The control algorithm consists of a combination of feedforward and feedback loops. A feedback controller is used to calculate the dosing rate to raise the sewage pH at the pumping station to the set-point. A feedforward controller is then used to calculate the additional dose based on the prediction of acid production in the downstream sewer pipe due to in-sewer processes. A further feedback controller is used to adjust the dosing rate to correct the error between the sewage pH at the end of the pipe and the pH set-point. Following comprehensive assessment using modeling and simulation, the control was successfully validated and its effectiveness demonstrated in a 2-month field study. The online control algorithm reduced the variation of pH at the discharge point, i.e., from to . In addition to improved sulfide control, the controller also resulted in 15% saving in chemical consumption, leading to significant financial benefits and lower environmental footprint. It was also found that the sewage flow rate should be predicted online for sewers influenced by rainwater infiltration as the variation of flow rate and sewage dilution are important disturbances for the controller.
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Acknowledgments
The authors acknowledge the financial support provided by the Australian Research Council and many members of the Australian water industry through LP0882016 the Sewer Corrosion and Odour Research (SCORe) Project (www.score.org.au). The authors would like to thank also South Australian Water, and specially Bevan Dearman and David Monceaux, for supporting the field trial, sampling campaign and data collection. Ramon Ganigué gratefully acknowledges support from Ghent University BOF postdoctoral fellowship (BOF15/PDO/068).
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Information & Authors
Information
Published In
Journal of Environmental Engineering
Volume 142 • Issue 12 • December 2016
Copyright
© 2016 American Society of Civil Engineers.
History
Received: Jan 26, 2016
Accepted: Apr 27, 2016
Published online: Jul 15, 2016
Published in print: Dec 1, 2016
Discussion open until: Dec 15, 2016
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