The City of Hamilton, Ontario has one of the largest combined sewer systems on the Great Lakes, conveying both wastewater and stormwater to the Woodward Avenue Wastewater Treatment Plant (WWTP). The Woodward Avenue plant serves a population of approximately 380,000, and has an average
day dry weather flow of approximately 350 ML/d. During wet weather, the flow entering the plant can be several times average dry weather flow. Flows that exceed the capacity of the plant bypass the treatment process and enter Hamilton Harbour via Red Hill Creek. The Woodward Avenue
plant has limited space available for the construction of the new treatment units that would be required to treat wet weather bypasses. High rate treatment technologies offer the ability to achieve high standards with relatively small footprints. Two well established high-rate clarification
technologies, Actiflo® and DensaDeg®, were of particular interest to the City, because they offered the potential to achieve the bypass treatment goals and, in addition, possibly allow the City to use the same treatment units as a tertiary “polishing” of dry weather flows
to meet harbour loading targets for total suspended solids and total phosphorus. The providers of both technologies were invited to demonstrate their units by pilot testing at the plant. The testing concluded that both processes are capable of meeting the Ministry of Environment (MOE) Procedure
F-5-5 standards, when treating wet weather flows, and Hamilton Harbour Remedial Action Plan (RAP) initial targets, when treating secondary effluent. Both processes were able to achieve considerably higher rise rates than enhanced primary treatment using conventional clarifiers. The pilot testing
also demonstrated that both processes can start-up very quickly for both wet weather flow treatment and polishing of secondary effluent. Concept designs and life cycle costs were developed for both processes, operating in CSO and dual treatment mode. At the conceptual costing level, the two
processes appear to be cost competitive and worthy of more detailed evaluations.
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