Dissolved air flotation (DAF)
In this process, wastewaters (or other waters) are clarified by the removal of suspended matter such as oil or solids. Pressurized air is dissolved in the water or wastewater and then is released at atmospheric pressure in a flotation tank or basin. Tiny bubbles which results by releasing air adhere to suspended matter causing them to float to the surface of the water; a skimming device may collect and remove them from the surface.
Air dissolution occurs within the air dissolving tank that is receiving either pumped raw flow or pumped recycle flow that will be mixed with compressed air or gas. The air/water mixture is then held under pressure in the air dissolving tank by a backpressure valve assembly. The backpressure valve injector releases the pressurized flow near the center of the flotation unit into a distribution well which allows the dissolved air to come out of solution in the form of microscopic bubbles. These small bubbles attach themselves to suspended solid particles contained in the waste stream and float them to the surface of the cell. The accumulated float is collected on the surface by multiple skimmer arms which move the solids into the float box. The clarified water exits the tank by passing down and under a full diameter baffle skirt, then rises up and over a peripheral effluent weir and out of the tank. Heavier solids that may settle to the basin floor are collected and removed with the rotating scraper arms.