Dissolved Air Flotation (DAF)

Dissolved Air Flotation (DAF) is a physio-chemical water treatment process that separates suspended solids, fats, oils, and grease (FOG) from wastewater by attaching fine micro-bubbles to contaminant particles, causing them to float to the surface for mechanical removal. DAF is widely deployed as a primary clarification stage ahead of biological treatment, as a secondary clarifier for reducing colour and turbidity, and as a sludge thickener in municipal sewage treatment plants.

The core of a DAF system is an Air Dissolving Tube (ADT) or pressurisation vessel in which air is dissolved into a recycle stream of treated water under pressure, typically 4–6 bar. When this saturated stream is released into the atmospheric-pressure flotation tank, the dissolved air comes out of solution as countless micro-bubbles measuring 10–100 microns in diameter. These bubbles attach to suspended particles, reducing their effective density and causing them to rise rapidly to the water surface as a floating sludge blanket, which is continuously removed by surface scrapers or paddles.

Chemical dosing — coagulants and flocculants — is integrated upstream of the DAF unit to destabilise colloidal particles and form larger, more buoyant flocs. This chemical pre-treatment significantly improves TSS and FOG removal efficiency, enabling DAF systems to handle highly variable and high-strength industrial effluents. Heavier solids that do not float settle to the tank bottom and are periodically purged as bottom sludge.

DAF units are available in rectangular and circular tank configurations to suit site constraints, and can be engineered for capacities from 5 m³/hr to over 1,000 m³/hr per unit. Clarified water exits from mid-tank outlet nozzles, suitable for discharge, reuse, or further biological treatment.