UPGRADING THE NORTH TORONTO COMBINED SEWER OVERFLOW (CSO) STORAGE AND TREATMENT FACILITY

摘要

Traditional CSO storage facilities can be environmentally upgraded by optimising their hydraulics and implementing chemically aided settling. In the case study presented for the North Toronto CSO facility, a number of structural measures serving to enhance the facility treatment rate and inducing favourable settling conditions in the settling basins were addressed by means of physical and computer modelling. A physical scale model was effective for establishing the hydraulic performance of the facility (flow rates, water levels, and changes in these parameters) and verifying a CFD model. The CFD model simulated well the hydraulic phenomena in the facility and will be used in the next study stage for particle tracking. With respect to chemically aided settling, the settleability of CSOs can be assessed well by elutriation testing. The choice of a coagulant/flocculant depends on the characteristics of the wastewater treated, including pH, dissolved organic matter contents and characteristics, and temperature. Jar testing offers the best way for selecting the most suitable chemical and its dosage. Finally, the solids removals in excess of those required by a provincial (Ontario) CSO control directive (primary treatment equivalency) were achieved at the facility studied with flow-proportional polymer dosing of 6-8 mg/L and the surface load rates of 15 m/h. Further refinements of settling conditions in the facility (by flow conditioning baffles), dosing (switching to solids flux proportional dosing) and higher surface loading rates are planned and will be assessed by both CFD modelling and field observations.