DAF:
DISSOLVED AIR FLOTATION
An Advanced Wastewater Treatment
What the DAF process does is to separate suspended contaminant particles from liquids, like oil and grease, by bringing them to the surface of the liquid. These light particles are thus easily removed using physical methods. DAF also facilitates efficient wastewater and process water treatment through flotation with micro bubbles.
The incoming wastewater into a DAF system usually requires pre-treatment. Chemical coagulant(s) and/or flocculant(s) are usually added and the adjustment of pH may may also be necessary to ensure optimum operating conditions for DAF.
Dissolved Air Flotation: Theory
Dissolved Air Flotation system is an advanced wastewater treatment used mostly in the industrial sector to treat wastewater algae, organics, oil and grease. It is very efficient for the reduction of Chemical Oxygen Demand (COD) present in fat, grease, oil, biological sludge, coloured organic matter, and colloidal material.
It is also excellent for removing oil and grease from industrial wastewater, as mentioned.
DAF has been used for treating drinking water clarification and treatment in several countries like the UK in Europe since the late 1960s and is a common method of choice in drinking water treatment systems in the US too since the 1980s.
DAF Pressure Floatation
Flotation is an extremely critical part of wastewater treatment. In pressure flotation what happens is that air is dissolved in water under high pressure and released at atmospheric pressure through a nozzle or needle valve to produce small air bubbles. These air bubbles then make the lighter contaminants and suspended matter in the wastewater float on to the surface of the water in the flotation tank, and these can easily be removed by a skimming device.
This is the reason, Dissolved air flotation is widely used in treating the industrial wastewater effluents from petrochemicals, oil refineries, and chemical plants where the effluent is made of lighter solids. General water treatments also use DAF for removing colour and organic particles like algae.
What the DAF process does is to separate suspended contaminant particles from liquids, like oil and grease, by bringing them to the surface of the liquid. These light particles are thus easily removed using physical methods. DAF also facilitates efficient wastewater and process water treatment through flotation with micro bubbles.
The incoming wastewater into a DAF system usually requires pre-treatment. Chemical coagulant(s) and/or flocculant(s) are usually added and the adjustment of pH may may also be necessary to ensure optimum operating conditions for DAF.
DAF Advantages
Process Efficiency
It gives higher quality effluent that can be safely discharged into the sewer system while fulfilling PCB compliances for industry effluents.
System Design and Flexibility
It boasts a compact design and a much smaller footprint in comparison to other wastewater treatment technologies/systems.
Chemical and Technology
DAF gives the flexibility of multiple chemical sampling and injection points to be included as per the requirements of the effluent.
Process Efficiency
It gives higher quality effluent that can be safely discharged into the sewer system while fulfilling PCB compliances for industry effluents.
System Design and Flexibility
It boasts a compact design and a much smaller footprint in comparison to other wastewater treatment technologies/systems.
Chemical and Technology
DAF gives the flexibility of multiple chemical sampling and injection points to be included as per the requirements of the effluent.
Process Efficiency
It gives higher quality effluent that can be safely discharged into the sewer system while fulfilling PCB compliances for industry effluents.
System Design and Flexibility
It boasts a compact design and a much smaller footprint in comparison to other wastewater treatment technologies/systems.
Chemical and Technology
DAF gives the flexibility of multiple chemical sampling and injection points to be included as per the requirements of the effluent.
Process Description
Flotation Tank - For introducing Bubbles
The flotation tank is divided into two zones: the front zone, where the contact of the dissolved contaminants happen with the flocculants that are introduced to trap them. It is also called the reaction zone. The other zone is the separation zone. A ‘baffle’ is fixed between the two to control flow. Small air bubbles are introduced into the contactor reaction zone. This part of the flotation tank is actually designed to form bubble–floc agglomerates. The bubble size is absolutely critical to form agglomerates. In DAF, small bubbles are required to achieve an actionable solid–liquid separation. Infact, a bubble size in the range of 50–100 μm is the most suitable for the DAF process. If the bubbles are larger, they may create turbulence in the flotation tank and, simultaneously, decrease the surface area of the particle-bubble attachment. To obtain the preferred bubble size, air is dissolved in a saturator under pressure delicately. The pressure controls the total amount of air introduced into the contact zone at any given time. Once the bubbles and contaminant particles come into contact through trapping, adhesion, or absorption process in the contact zone, the bubble–floc aggregates move on to the separation zone so that the process water can be clarified.
Industries that use DAF for their wastewater treatment
