Dissolved Air Flotation (DAF)
DAF systems are designed to remove suspended solids along with fat, oils and grease (FOG) from a waste stream by flotation, as opposed to gravity separation. DAF systems work exceptionally well in waste streams that include solids that tend to remain in suspension or float such as food, chemical, and petroleum-based waste streams.
Prior to the DAF, the wastewater must be chemically treated by pH adjustment, coagulation, and flocculation. DAF systems are designed to remove the solid particles formed by the coagulation and flocculation processes by using very small air bubbles that attach to the floc particles causing them to float to the surface for removal by skimming.
The tiny bubbles are formed by injecting air under pressure into a wastewater recirculation stream. This recirculation loop uses 10% to 30% of the discharge from the DAF. This air-saturated recirculation stream is returned back to the influent of the DAF for mixing with the incoming, untreated wastewater. When the pressurized water is suddenly released to atmospheric pressure, the air comes out of solution and creates very fine air bubbles (whitewater) that attach and enmesh to the solid particles causing them to float.
DAF systems are equipped with a skimmer for removing the “float” into a sludge hopper. The float is then transferred to the solids handling system for further processing.
Many DAF systems incorporate a pipe flocculator for mixing and dosing coagulants and flocculants instead of conventional tanks and mixers. The pipe flocculator is a serpentine section of pipe fitted with chemical injection ports and flow restricting orifices that create turbulence and mixing of the wastewater and chemicals. Pipe flocculator systems take up less space than conventional mixing systems.