CSO PLANNING: INTEGRATED COLLECTION SYSTEM AND WASTEWATER TREATMENT PLANT HYDRODYNAMIC SIMULATION

The City of Edmonton's Gold Bar Wastewater Treatment Plant (GBWWTP) is at the downstream end of a collection system servicing approximately 634,000 people plus industrial and commercial areas. The plant has a relatively flat hydraulic profile, where the effluent weir on the primary tanks is 0.23 m above the invert of the incoming conduit and the effluent weir on the secondary clarifiers is only 0.38 m below the primary tank weir.Hydraulic simulation of the collection system has proceeded on the assumption of a controlled head relationship at the headworks of the treatment plant. As work progressed on the City's Combined Sewer Overflow Strategy and a preferred method of control was to convey more flow to the GBWWTP for treatment and expand treatment capacity, the hydraulic gradeline at the inlet and the headworks of the plant became more significant as hydraulic elements. Without lowering the gradeline at the plant inlet, it was found to be difficult to achieve the objective of treating a flow rate of 1600 ML/D on a sustained basis and using this capacity without premature combined sewer overflows (CSO) upstream of the plant when the plant still had treatment capacity. These conditions made it necessary to lower the hydraulic profile at the plant and simultaneously evaluate the system flows.To understand and evaluate the hydraulic relationship between the upstream collection system and the GBWWTP a detailed hydraulic model was developed and included as part of the collection system hydraulic model. The hydraulic model was constructed in the Danish Hydraulic Institute MOUSE model using approximately 150 elements to describe the various treatment processes. This included grit tanks, screens, primary settling basins, bypasses, secondary aeration basins, secondary clarifiers, ultra violet disinfection, and outfall to the river.This paper discusses the hydraulic relationship between the collection system and the treatment plant, provides details on the structure of the treatment plant hydraulic model and the approach used to integrate the collection system and treatment plant hydraulic modeling activities to evaluate CSO Long Term Control strategies for the City.