Dissolved Air Flotation (DAF) System

Dissolved Air Flotation (DAF) System is an important unit of operation in wastewater treatment plant, which is used to separate oils and others solid particles from its liquid phase. It involves both mechanical and chemical mode to achieve a good separation and basically this is made possible by introducing fine gas, usually by using compressed air bubbles injected into the liquid phase. The flotation system here is a very crucial step that removes the solid waste resulting in high reduction of COD and BOD before proceeding to the next step of wastewater treatment processes.

The principle that enables the system to work is by using buoyant force of the combined waste particle and gas bubbles which will both attach together and then rise to the surface so that this can then be skimmed off easily by using mechanical scrapper. In this case, air will act as a flotation agent to facilitate removal of unwanted materials. In today’s industrial wastewater treatment plant, flotation can be a very effective method to remove suspended matter and to concentrate biological sludge before sending to aeration pond; and then finally to dewatering phase before moving to effluent discharge. The advantage of using flotation over sedimentation is that, smaller and lighter particles that settle slowly can be removed more thoroughly, which is otherwise almost impossible to achieve without the flotation system.

In dissolved air flotation (DAF) unit, pressurized air is introduced at the pump discharge point and the wastewater will then be diverted to a retention tank so that this will allow the air to slowly dissolve into the water. This will then be followed by release of the accumulated pressure that goes through either a pressure- reducing valve or control valve (for better adjustment of water flow) back to the flotation tank. Once the water is exposed to normal atmospheric level, fine air bubbles will float to the top and will carry along with it all the attached particles to the surface. In other conventional DAF systems, the unit of operation might be differ slightly, in which the recycled flow is mixed with unpressurized water stream just before going back to the flotation tank. Either way, all systems operate on the same principle to achieve a good separation.

For more information you can refer to this article that goes into details studying different options available and the types of flotation systems that should be selected depending on the applications.

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