Just 24 months after the Mayor of the Town of Renfrew, Sandi Heins, officially broke ground at the site of the town’s future STP, the state-of-the-art secondary sewage treatment facility was commissioned, and has been producing “near tertiary” quality effluent ever since. The original plant, designed by our firm in the late 1960s, had served Renfrew well, but was in need of an upgrade due to its age and ability to provide primary treatment only. Before the ground-breaking ceremony, our firm was retained as part of a consulting group that also included CH2M HILL, XCG Consultants, and Trow Consultants to design and oversee the construction of the new plant.
Topography, soils, and footprint restrictions presented a number of challenges during design. The original Class Environmental Assessment (EA) suggested that components of the existing plant be incorporated into the new works. However, during a value engineering session, the preliminary design concepts were revamped and it was decided that a new facility located at a nearby site would provide better long-term value. From that point on, designers carefully fine-tuned the plant layout to ensure optimal functionality, as well as flexibility for future expansion. This flexibility included designing the aerated digester to be converted to a third aeration tank, if and when required, and allowing for sufficient space and tie-ins for the possibility of a third secondary clarifier. The plant was also sized to ensure full capture of high peak flows generated within the sanitary collection system, avoiding the need for any separate wet weather treatment system.
An important cost-saving measure identified for interim operation of the old plant involved the temporary installation of a rotary (or “Fournier”) press, the first such installation in Ontario, to dewater liquid biosolids that were previously being hauled to the City of Ottawa, which was extremely expensive. By installing this equipment at the old plant, Renfrew saved hundreds of thousands of dollars. The equipment was later relocated to the new plant as a back-up to the main centrifuge dewatering equipment. Other features of the plant include septage receiving, screening and degritting, an extended aeration treatment process, ultraviolet disinfection, chemical feed systems, standby generator, and administration facilities, including a laboratory, offices, and a service garage.