WCW24

This presentation will showcase a unique hybrid DAF technology implemented at the Ruthven Water Treatment Plant in Southwestern Ontario and will cover the existing system, the basics of DAF, how the new hybrid DAF was integrated into the existing system, and the performance since construction. The raw water source for the plant is Lake Erie. Lake Erie is the shallowest and warmest of the Grate Lakes, which leads to frequent and severe algae blooms often concentrated near the plant's intake. Additional challenge is posed by so-called high turbidity events (HTE), i.e. periods when lake sediments are disturbed either by storms on the lake or by pulsing river discharge. The turbidity of raw water intake may exceed 400 NTU. Water treatment systems in such conditions need to be able to simultaneously and effectively remove solids that naturally tend to float, like algae and heavier mineral suspension which tends to settle. The existing treatment plant comprised of upflow clarifiers followed by gravity sand filters. The clarifiers were effective in the removal of heavier mineral solids but struggled with removing algae. A pilot test of a conventional DAF proved that DAF would be able to remove the algae, but it could be overwhelmed with mineral solids during HTE. The project team chose a third option: combining the two technologies for a different solution. In 2020, the project converting one of the clarifiers to a hybrid DAF commenced. The clarifier mechanism was completely removed and a new internal mechanism including flocculation well, reaction zone, new scum throughs and sludge rakes was installed. The result was a system that effectively doubled the unit capacity without increasing its footprint. The new hybrid system proved to be easy to operate, and resilient to both fluctuating water demands and fluctuating intake characteristics.