Computational Fluid Dynamic Modeling of a Hydraulic Flocculator for the Charles-J.-Des Baillets Water Treatment Plant (City of Montreal)

«ABSTRACT: This study aims to provide a sustainable and resilient solution to address the adverse impacts of climate change on the water source quality of the Charles-J.-Des Baillets water treatment plant. Increased occurrence of storms may lead to significant increases in turbidity on certain days leading to a decreased efficiency of the filtration process. Accordingly utilizing a hydraulic flocculator prior to direct filtration is proposed to improve turbidity removal and increase the length of filtration cycles. Analyzing the function and efficiency of this flocculator with two configurations (8 or 16 baffles) was performed utilizing Computational Fluid Dynamics (CFD) through OpenFOAM in addition to an experimental study to define flocs growth kinetics according to the Camp number (Gt). The results indicate that adding baffles upstream from the filters can effectively create the necessary head loss to perform hydraulic flocculation. Moreover, velocity analysis revealed distinctive flow pattern variations and recirculation lengths, with the 16-baffle setup demonstrating a more consistent and controlled flow, potentially impacting overall flocculation efficiency. Examining velocity gradient (G value), the 16-baffle configuration significantly narrows the range to from 10 s-1 to 500 s-1, indicating superior flow control compared to the wider range, 10 s-1 to over 1000 s-1, observed in the 8-baffle channel. In addition, qualitative assessment of Camp number (Gt) illustrates a notable Gt increase after adding baffles, the current Gt in the channel without baffle is lower than 10,000, while the 16-baffle channel is experiencing higher Gt values of 53,000 and the 8-baffle setup has the Gt value of 26,000 at the flocculator exit, which aligns with the lower range of typically used Gt.»