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Dissolved Air Flotation to Treat Industrial Wastewater

In dissolved air flotation, a change in pressure produces microbubbles that float impurities to the surface of a liquid.

Learn how DAF works, and why it’s effective at treating industrial wastewater

Dissolved air flotation (DAF) is a wastewater treatment process that effectively clarifies water or wastewater by removing suspended solids from liquids. It uses dissolved air to float solid particles to the surface, where they are removed by a skimmer. The liquid being treated can be sewage, liquid sludge, or raw water.

DAF is commonly used to treat water and domestic sewage, as well as wastewater from various industrial facilities, including paper mills, chemical plants, natural gas operations, oil refineries, and petrochemical plants.

How Dissolved Air Flotation Works

A DAF system is comprised of four key components:

  • An air supply
  • A high-pressure pump
  • A retention tank (saturator)
  • A flotation tank

Air is pumped into liquid in a retention tank under a pressure of 25-90 psi (172-620 kPa) and left for three to 30 minutes to allow the air to dissolve into the liquid.

The liquid then passes through a pressure-reducing valve to the flotation tank, which operates at atmospheric pressure. The sudden drop in pressure releases the dissolved air from the water in the flotation tank, forming microbubbles that attach to the suspended solids and carry them to the surface.

A coagulant or a flocculant is often added to the mixture to bring the particles together. A skimmer is then used to remove solids on the surface, and the clarified effluent exits the DAF system.

DAF Also Suitable for Oily Wastewater

DAF treatment is not limited to particulate matter, it can also be used to separate oil from water. Industrial wastewater can contain a variety of oils and oil components, including lubricating oil, crude oil, and animal fats, depending on the industry. DAF treatment causes air to attach to oil droplets in an emulsion, helping them rise to the surface of the wastewater.

In the petroleum industry, dissolved gas flotation (DGF) systems reduce explosion risk by using nitrogen gas rather than oxygen-containing air to create microbubbles. DAF and DGF offer simple, efficient, and cost-effective methods of separating oil from an oily emulsion without any risk of secondary contamination.

DAF systems can be either circular or rectangular in design. Circular systems are more efficient and can take just three minutes to separate particles or oil droplets from wastewater, whereas rectangular systems typically take 20-30 minutes. The separation efficiency of a DAF system can be enhanced by incorporating parallel plates, or lamellas, into the system design.

Improving Efficiency, Cutting Costs With Dissolved Air Flotation

Fluence can install a stand-alone DAF treatment system or a wastewater treatment system consisting of DAF and a combination of other treatment technologies, depending on your requirements.

For example, Fluence upgraded the wastewater treatment plant at a fish processing plant in Ecuador, helping the company to improve the quality of its wastewater effluent, reduce the volume of disposable waste generated, and also cut energy costs.

The original plant was upgraded to include DAF, anaerobic digestion, double-stage nitrification-denitrification, and final clarification. The upgraded waste-to-energy plant has reduced energy consumption by up to 40% and cut wastewater treatment costs by 50%, saving the company more than $120,000 a year.

Contact Fluence’s team of wastewater experts to learn more about DAF and other wastewater treatment solutions, and how we can help you improve efficiency while cutting costs.

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