Dissolved Air Filtration Flotation (DAFF) is a water treatment process used as an alternative to sedimentation. Due to certain inlet (raw) water quality characteristics (e.g. oil presence, high colour and low turbidity), traditional sedimentation techniques are not suitable and thus, the DAFF process is preferable.

Basic Process
Raw water enters the plant where it is initially dosed with a coagulant like metal salts (mostly ferric chloride or aluminium sulphate) to coagulate to break the double charged layers around the contamination in the raw water. During intense mixing small flocs are created, which then will be treated with a flocculant the create larger flocs. The water then will pass into several flocculation tanks depending on the process. The chemical like could be other than alum and even the scheme could be implemented without any chemical depending on process to process. The process of dissolved air generation and separation is identical as observed in aerated water bottle. This is where the DAFF process differs from the sedimentation process.

In the typical sedimentation process the flocculant (floc particles) - the coagulated material - is allowed to fall to the bottom in large sedimentation tanks. In the DAFF process, high pressure product water (from the end of the plant) is saturated with air and then released up into the flocculation tanks. This causes a sudden pressure drop which releases small bubbles of air. These bubbles effectively 'lift' the flocculant to the surface of the flocculation tank. This flocculant then remains on the surface where it is either scraped off or overflows (by deliberate raising of the tank water level).

The water then travels down through a filter which is typically either sand or multimedia (anthracite-sand-gravel). This removes any floc particles which didn't properly rise to the surface.

The rest of the process is the same as the sedimentation process whereby the sludge (floc particles and water) is further dried and then this water (supernatant) is returned to the front of the plant. Also, the product water is then adjusted for pH and fluoride added. Note: these two steps may differ slightly between plants (e.g. sludge put down the sewer where it is treated).