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Friday 07 Feb 2020Impact of hydraulic paths on chlorine degradation in water distribution systems

Prof Genevieve Pelletier - Universite Laval, Canada

Harrison 103 14:35-15:25


The research program was designed to develop methodologies to predict free residual chlorine (FRC) and disinfection by-products (DBPs, mainly THMs and HAAs, and some emerging contaminants) in water distribution systems (WDS) through microbiological and chemical reactions in the bulk volume and at the pipe walls along hydraulic paths dependent on instantaneous water demands. Predicted FRC and DBP concentrations are used by operators, managers and engineers to reduce the microbiological risks in vulnerable areas of a WDS and to manage disinfection cost-effectively. Intensive and seasonal sampling campaigns were conducted to evaluate FRC and DBP concentrations at the neighbourhood scale. Hydraulic models were then calibrated by adjusting the chlorine pipe wall coefficients to obtain the best fit between predicted and observed field measurements (total decay), after fixing bulk volume coefficients from laboratory analyses. The predictive model for FRC concentrations simply uses first-order decay for both the bulk volume and pipe wall kinetics; for DBP, it is more complicated… The hydraulic and water quality model enables the simulation of FRC concentrations for different bulk volume and pipe wall kinetics and/or water demand scenarios. The methodology was tested on three neighbourhood-scale WDS in the Quebec City region (Canada) with populations ranging from 6,900 to 18,700. As expected, a decrease in FRC concentrations was observed due to flow reduction from both local repairs of leaks and breaks (-10%) and global water conservation strategies (-20%). This is mainly because FRC concentrations are strongly impacted by the increase in mean residence time in WDS from lower water demands and by the change in hydraulic paths according to instantaneous water demands. Results showed that an increase in initial FRC concentrations ranging from 7% to 13% ($) in our case studies is required to obtain similar FRC concentrations in the WDS when realistic flow reductions are applied.


Prof. Genevieve Pelletier is a full professor in the Department of Civil & Water Engineering at Universite Laval and the Water Engineering undergraduate program director (when not on sabbatical leave). She obtained her engineering degree from McGill University in Agricultural Engineering (1990), her MSc in Civil Engineering from the University of Ottawa (1995) and her PhD in Water Science from INRS in Quebec City (2000). She then worked for six years in water engineering for an international consulting firm before obtaining a tenure-track position at Universite Laval in 2005 targeted for their new water engineering program.

She specializes in urban hydraulics and, more precisely, in the integrated management of all urban waters. She develops methodologies and tools to help water managers and engineers integrate water quality, real-time control and climate change aspects in the planning, design, operation and rehabilitation/renewal of drinking water distribution and wastewater, combined water and stormwater collection systems. She mainly works within two research teams: Universite Laval-NSERC Industrial Research Chair in drinking water quality (Chair holder: Dr. Manuel Rodriguez) and a stormwater research group with Prof. Sophie Duchesne (INRS) and Prof. Paul Lessard (Universite Laval).

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