Retrofitting Clarifiers to DAFs for Intensified Solids Separation
Wednesday, September 30, 2026 9:00 AM to 9:30 AM · 30 min. (US/Central)
New Orleans Convention Center
Technology Spotlight
Hall H Booth 7249
Information
Utilities treating highly variable surface water increasingly face the need to intensify solids separation within constrained footprints while improving resilience to algae, turbidity spikes, and hydraulic fluctuations. This session presents a case study of a clarifier-to-DAF retrofit implemented at the Ruthven Water Treatment Plant (WTP) in Kingsville, Ontario, where a conventional circular clarifier was converted into a hybrid dissolved air flotation (DAF) system.
Kingsville's experience has proven retrofitting legacy clarification basins with a hybrid flotation system can increase treatment capacity and improve performance under challenging influent conditions typical of Lake Erie source water, including seasonal algal blooms and rapid water quality changes. The DAF conversion incorporated rapid mixing, flocculation, air-saturation recycle, surface skimming, and bottom sludge removal within the existing tank geometry.
Findings highlight the needs to apply DAF, a high-rate separation process to handle performance challenges on surface water treatment, where algae and higher level of organics in water cause poor performance from conventional gravity clarifiers. DAF systems, which employ microbubbles (10–40 µm) to float low-density particles, are particularly effective for algae, lighter flocs and fine solids that do not settle well in lamella or gravity clarifiers. The hybrid DAF approach integrates flotation and sedimentation mechanisms, enabling simultaneous removal of both buoyant and settleable fractions and doubling capacity relative to the original clarifiers under equivalent footprint constraints.
Key design considerations identified include effective coagulation and flocculation process, even flow distribution, sufficient scum removal system, and reliable air saturation system, and the retained ability to remove heavy solids through the bottom sludge scraper mechanisms. Retrofit-specific challenges-such as customized engineering adapting to the existing circular tank and piping, innovative field erection method and schedule management to shorten plant down time, are discussed alongside lessons learned during startup and phased implementation.
Operationally, the system employs a moderate-to-high level of automation, including factory-integrated saturation skids, mechanical skimmers, and process controls, reducing operator intervention to routine monitoring and chemical adjustments.
The significance of this work lies in demonstrating a practical pathway for intensifying conventional treatment plants through hybrid, high-rate separation technologies. Attendees will gain actionable insights into technology selection, design trade-offs, and retrofit strategies that enhance robustness to flow and water quality variability, while leveraging existing assets to defer capital-intensive expansions.
Kingsville's experience has proven retrofitting legacy clarification basins with a hybrid flotation system can increase treatment capacity and improve performance under challenging influent conditions typical of Lake Erie source water, including seasonal algal blooms and rapid water quality changes. The DAF conversion incorporated rapid mixing, flocculation, air-saturation recycle, surface skimming, and bottom sludge removal within the existing tank geometry.
Findings highlight the needs to apply DAF, a high-rate separation process to handle performance challenges on surface water treatment, where algae and higher level of organics in water cause poor performance from conventional gravity clarifiers. DAF systems, which employ microbubbles (10–40 µm) to float low-density particles, are particularly effective for algae, lighter flocs and fine solids that do not settle well in lamella or gravity clarifiers. The hybrid DAF approach integrates flotation and sedimentation mechanisms, enabling simultaneous removal of both buoyant and settleable fractions and doubling capacity relative to the original clarifiers under equivalent footprint constraints.
Key design considerations identified include effective coagulation and flocculation process, even flow distribution, sufficient scum removal system, and reliable air saturation system, and the retained ability to remove heavy solids through the bottom sludge scraper mechanisms. Retrofit-specific challenges-such as customized engineering adapting to the existing circular tank and piping, innovative field erection method and schedule management to shorten plant down time, are discussed alongside lessons learned during startup and phased implementation.
Operationally, the system employs a moderate-to-high level of automation, including factory-integrated saturation skids, mechanical skimmers, and process controls, reducing operator intervention to routine monitoring and chemical adjustments.
The significance of this work lies in demonstrating a practical pathway for intensifying conventional treatment plants through hybrid, high-rate separation technologies. Attendees will gain actionable insights into technology selection, design trade-offs, and retrofit strategies that enhance robustness to flow and water quality variability, while leveraging existing assets to defer capital-intensive expansions.