AC25 Advancing Solids Thickening Through Suspended Air Application

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Presentation Description: In a recent project funded by California Energy Commission (CEC), an innovative thickening process -Suspended Air Flotation (SAF®)- was selected to be tested at demonstration scale. SAF® process presents a compelling alternative to traditional thickening methods considering its potential to reduce energy consumption and to separate emerging contaminants such as Per- and polyfluoroalkyl substances (PFAS).

The SAF technique employs a suspension of micron-sized air bubbles, ranging from 7 to 50 µm, in water to attain a volumetric air content of 40 to 50%. These bubbles are coated with a thin layer of soap film derived from an electrically charged anionic or cationic surfactant. The charged bubbles offer a substantial interfacial area for the adsorption of oppositely charged flocculated wastewater solids. In practice, suspensions of charged bubbles are introduced into the flotation tank to interact with wastewater solids. The solids then ascend to the surface and are skimmed off. The clarified effluent is recirculated to the headworks.

SAF enhances traditional thickening methods like Dissolved Air Flotation (DAF) by eliminating the need for dissolved air, thus obviating the requirement for pressurization systems, recirculation pumps, compressors, and airlines, leading to considerable energy savings. SAF's capability to manage high solids loads also results in substantial footprint and power savings, high solids recovery (up to 99%), and a high solids loading rate (up to 40 lb/ft2/hr). Moreover, no polymer is needed to thicken sludge to 4% solids. Owing to these benefits, adopting SAF technology can lead to an energy savings of up to 90% compared to its conventional counterparts, such as DAF.
This presentation will assess this novel technology, its performance, present results from case studies, and elaborate on the potential of this technology for PFAS separation.

Learning Objectives:
Define the suspended air flotation technology (SAF) and difference between dissolved air flotation (DAF) technology
Demonstrate the advancements of SAF technology for various case studies including thickening of Advanced primary treatment solids and secondary solids
List the important criteria for the design and operational challenges of the SAF technology

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