The Region of Waterloo’s Galt Wastewater Treatment Plant in Cambridge, ON has provided advanced treatment of the area’s wastewater since the 1950s. The wastewater treatment facility comprises nitrifying activated sludge reactors to biologically treat the wastewater, followed by secondary clarifiers where activated sludge settles and is removed, tertiary filtration of secondary effluent (treated liquid), and ultraviolet disinfection.
The facility was expanded and upgraded in 1992 to create two parallel treatment trains, Plant A (original) and Plant B (new), and increase capacity to 56,800 cubic metres per day (average day flow) and 171,000 cubic metres per day (peak hour flow).
By 2013, the facility, which is operated by the Ontario Clean Water Agency, was experiencing operational issues. The Region retained Associated Engineering to resolve issues related to solids carrying over to and clogging tertiary sand filters under peak flow conditions. Also, during peak hour flows, if one of the Plant B clarifiers was shut down for maintenance, partially treated wastewater would overflow from the common inlet distribution chamber into the secondary effluent chamber, flowing to and clogging downstream filters.
In addition, during warm weather, algae would grow in the clarifier launders (effluent channels). Algae would clog downstream filters, reducing treatment capacity, and creating maintenance problems.
The Region identified that the clarifier mechanisms (rotating sludge collection equipment in the clarifiers) in the two Plant B secondary clarifiers needed to be upgraded to allow the plant to function successfully. Design Lead and Senior Environmental Engineer, Nancy Liu tells us, “There are many older circular secondary clarifiers, like those at the Galt facility, that use draft-tube-type sludge collection mechanisms. As these clarifier mechanisms approach the end of their service life, there is an opportunity to replace them with new mechanisms which can significantly improve clarifier performance and solve operational issues.”
The process design team evaluated various clarifier mechanism technologies. A suction header sludge collector in conjunction with a multiple-plate-type energy dissipating inlet, large diameter feed well, density current baffles, and effluent launder covers were recommended for the clarifier upgrades.
Significant leakage at the clarifier inflow isolation sluice gates created challenges for upgrading the clarifier mechanisms, and complicated construction. Nancy advises, “The sluice gates were essential to isolating the clarifiers and performing the upgrades, as well as ongoing maintenance of the clarifiers in the future. Replacing the sluice gates required significant effort. We designed a temporary bypass pumping system, as well as custom, temporary, high pressure, inflatable, isolation bags to isolate yard piping and facilitate replacing the sluice gates. Once completed, the clarifiers could be isolated and the mechanisms replaced.”
Project Manager, Ed Salenieks says, “Upgrades to the existing secondary clarifiers solved the hydraulic capacity issues, and improved overall plant performance, lowering the total solids and total phosphorus in the treated effluent. Covering the effluent launders blocks sunlight to the effluent, controlling algae growth.”
Key staff involved in the project included Ed Salenieks, Nancy Liu, Kevin Yu, Paul Shi, David Holyer, Jimmy Looi, and Melissa Reichert-Kilbey.