Physical and computational modelling of residence and flow development time in a large municipal disinfection clearwell

Abstract

In this study, a two-dimensional, depth-averaged computational model (River2DMix) was used to predict the flow pattern and residence time distribution for flow through the Calgary Glenmore Water Treatment Plant northeast clearwell. Results are compared to those from flow visualization and tracer studies in a 1 : 19 scale model of the clearwell, as well as tracer studies conducted at the plant. Tests were carried out for three flow rates that ranged from minimum to maximum operating conditions. A key observation in the physical model was that it was necessary to let the flow fully develop before starting a tracer test to determine the residence time distribution. This flow development time to achieve steady-state results was approximately 10.5 h at the minimum flow rate tested. Results also show that it was unnecessary to model the structural columns either in the simulation or the scale model for developed flow in this clearwell, although for undeveloped or transient flow conditions the columns were important to consider.