In order to separate the suspended finely dispersed solid particles, wastewaters are conveyed to the flotation unit. Dissolved air flotation (DAF) has been successful in treating industrial wastewater effluents from oil refining and chemical enterprises, companies of food or pulp and paper industries and from other numerous industry fields in particular.
The flotation installation consists of the following components:
- Feeding pumps
- Float tank
- Sludge pumps (conveying sludge for dewatering)
- Air saturation path (incl. air blowers, pressure tank and pump)
- Coagulant, NaOH and polymer dosing tank stations
Coagulant * flocculants * feed water * froth * sludge * saturation pump * aeration valve * air * recycle flow * outlet water
Image 2 The layout of a flotation process
The process of flotation is achieved by dissolving air in wastewater effluents under pressure and then releasing the air at atmospheric pressure in a flotation tank or basin. The released air forms tiny bubbles which adhere to the insoluble matter causing it to float to the surface of the water where it may then be removed by a scraping device. A portion of the clarified effluent water leaving the DAF tank is pumped into a small pressure vessel (called the air drum), into which compressed air is also introduced. This results in saturating the wastewater effluents with air under pressure at the inlet. The air-saturated water upflow is recycled to the front of the float tank and flows through a pressure reduction valve the same way it enters the front of the float tank, i.e. the air being released in the form of tiny bubbles. The latter adhere to the suspended particles causing the suspended matter to float to the surface and form a froth layer, which is then removed by a skimmer, while the clarified water effluent exits the float tank.