Dissolved Air Flotation

Fluence’s dissolved air flotation (DAF) systems provide high-quality, efficient clarification of suspended particles from wastewater

Quick Removal of Oils and Buoyant Particles

Dissolved air flotation (DAF) uses microfine bubbles to float greases, oils and solids to the surface, from where they’re removed.

Fluence has been developing and continually improving dissolved air flotation (DAF) systems for decades, and has successfully implemented installations in a variety of applications.

DAF is a wastewater clarification process for the separation of solids, grease, and oils. The system helps concentrate sludge, removes a wide range of suspended solids (fats, oil, and grease) in wastewater and reduces COD and BOD. Our dissolved air flotation solutions provide high-quality, high-capacity, and efficient clarification.

DAF works by producing a stream of microfine bubbles that attach to solids and lift them to the surface, where they can be removed by a surface scraping mechanism.

Extensive Applications

DAF systems can be applied as a pretreatment to meet a municipality’s specific limits for oil, grease, or suspended solids, or to remove contaminants that would negatively impact an industrial biological wastewater treatment system downstream.

DAF technology is ideally suited to neutral-density particles and those that are buoyant or settle slowly. This is particularly relevant to the food industry and other businesses that produce light, high-volume solids that are resistant to settling. DAF also takes up about 25% of the equivalent surface area compared to conventional clarification technologies.

DAF is a proven, robust, and effective physical-chemical technology commonly used for many industrial and municipal applications, including:

  • Product recovery and reuse
  • Pretreatment to meet sewer discharge limits
  • Pretreatment to reduce loading on downstream biological systems
  • Polishing of biological treatment effluent
  • Removing silt and grease from industrial water

DAF is used extensively in the following industries:

  • Meat, poultry, and fish processing
  • Dairy industry
  • Petrochemicals
  • Pulp and paper
  • Food and beverage
How Dissolved Air Flotation Works

The flotation process is based on coagulation and flocculation mechanisms. By adding specific chemicals, such as iron chloride and aluminum chloride, colloidal particles are destabilized and floc formation takes place. Flocculation with other chemicals, such as polyelectrolyte, facilitates the collision between the destabilized suspended and colloidal particles to form larger clots that can be readily removed.

The process separates solid particles from the liquid. At first water is saturated with dissolved air under pressure. This recycle stream (pressurized from 4 to 6 bar), called the hypersaturated stream, is then mixed with the incoming wastewater in an internal contact chamber, where the microscopic air bubbles attach to solids and float them to the surface, forming a floating sludge bed.

A scraping assembly skims the sludge from the surface of the water and into a sump, from where it’s pumped to sludge treatment. The treated water is then discharged or undergoes other treatment processes.

Solution Architecture
  • The flotator is made of AISI 304 stainless steel and equipped with a flocculate accumulation basin.
  • The flocculate scraper is composed of a driveshaft with two gears at its extremities; a secondary shaft, also with two gears; two transmission chains that transmit the motion from the driveshaft to the secondary shaft; and four rubber scraper blades on the two chains.
  • The hypersaturation system is composed of a centrifugal multi-impeller pump equipped with valves and a delivery pipeline. The reserve unit will be supplied but not assembled. The pumps’ electric motors are not included.
  • An air-injection device in the pump body
Key DAF Features
  • Total suspended solids (TSS) reduction up to 97%
  • Chemical oxygen demand (COD) removal up to 85%
  • Low-cost operation and maintenance
  • Standard and customized units meet a variety of application and flow ranges
  • Designed for ease of installation and use
  • Suitable for high-salinity water

Efficient Dissolved Air Flotation Systems

At Fluence, our experienced process designers and field personnel offer support during all stages of the project, from preliminary design through commissioning and operation. Our highly reliable solutions are designed and customized to handle a wide range of influent quality and flow rate. Our DAF solutions are robust and compact. They are easy to install, operate and maintain.

Contact our experts to learn more about dissolved air flotation, or to discuss your specific project details.

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