DAF and SAF: Performance, Tradeoffs, and Retrofit Approaches for Municipal Sludge Thickening
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
High rate flotation systems are a valuable part of many municipal wastewater treatment plants. Dissolved air flotation (DAF) has long been a trusted and reliable option for sludge thickening, and suspended air flotation (SAF) is a newer approach that changes how air is introduced and how solids are contacted. This session will be co-authored and co-presented by WesTech, with extensive experience in DAF systems and Heron/Komline, with specialized expertise in SAF technology. While both technologies rely on air bubbles to float solids, they behave differently and each has its own strengths and limitations. This Technical Spotlight focuses on how to choose between DAF and SAF for municipal secondary clarifier sludge thickening as well as co thickening with primary sludge.
The presentation begins with a practical comparison of DAF and SAF fundamentals. A bench-scale DAF demonstration unit will be used to show how air is dissolved and then released in a DAF to float solids. This will be compared with a SAF to illustrate the differences in air distribution, surfactant use and loading capabilities. The discussion includes where each technology tends to perform best and how sludge characteristics (including WAS‑only versus blended primary and secondary sludges) and available footprint impact each approach. Polymer use, loading rates, equipment requirements and energy costs will be presented and contrasted for both options.
The session will include a presentation on a full scale DAF to SAF retrofit at a municipal Wastewater Treatment Facility in Sauk Centre Minnesota. The facility operates a WesTech rectangular DAF system for waste activated sludge thickening. As loading increased over time, the existing DAF became capacity limited and more demanding to operate. Rather than expanding the facility, the utility partnered with WesTech and Heron to convert the existing DAF to a SAF process, which allowed the to keep the same tank and many of the same internals. Following the retrofit, the SAF system handled significantly higher hydraulic loading while reducing total operating time. Energy and polymer consumption were reduced, and the resulting decrease in biosolids volume helped with storage and hauling.
The session concludes with a case involving a large metropolitan utility challenged by increasing load and limited expansion options. The discussion outlines how a DAF‑to‑SAF retrofit can address these constraints and contrasts design considerations at large scale for both circular and rectangular DAFs.
The presentation begins with a practical comparison of DAF and SAF fundamentals. A bench-scale DAF demonstration unit will be used to show how air is dissolved and then released in a DAF to float solids. This will be compared with a SAF to illustrate the differences in air distribution, surfactant use and loading capabilities. The discussion includes where each technology tends to perform best and how sludge characteristics (including WAS‑only versus blended primary and secondary sludges) and available footprint impact each approach. Polymer use, loading rates, equipment requirements and energy costs will be presented and contrasted for both options.
The session will include a presentation on a full scale DAF to SAF retrofit at a municipal Wastewater Treatment Facility in Sauk Centre Minnesota. The facility operates a WesTech rectangular DAF system for waste activated sludge thickening. As loading increased over time, the existing DAF became capacity limited and more demanding to operate. Rather than expanding the facility, the utility partnered with WesTech and Heron to convert the existing DAF to a SAF process, which allowed the to keep the same tank and many of the same internals. Following the retrofit, the SAF system handled significantly higher hydraulic loading while reducing total operating time. Energy and polymer consumption were reduced, and the resulting decrease in biosolids volume helped with storage and hauling.
The session concludes with a case involving a large metropolitan utility challenged by increasing load and limited expansion options. The discussion outlines how a DAF‑to‑SAF retrofit can address these constraints and contrasts design considerations at large scale for both circular and rectangular DAFs.
