Dissolved Air Flotation (DAF) Systems

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Our dissolved air flotation systems provide high-quality, efficient clarification for suspended matters such as solids, oil, and grease.

Dissolved air flotation (DAF) is a water clarification process for the separation of solids, grease, and oils. The advantages of DAF systems are in wastewater sludge thickening and in the ability to treat a wide range of suspended solids (fats, oil, and grease) in water at a high rate of removal.

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.

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 considerably less space than settling methods, generally requiring less than 25% of the equivalent surface area.

DAF is a proven 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
  • Removal of silt and grease from industrial water

The DAF Process

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 overall process separates solid particles from the liquid by saturating water with dissolved air under pressure into a recycle stream of clarified DAF effluent. 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 off the surface of the water and into a sump, from where it is pumped to sludge treatment. The treated water is then discharged or undergoes other treatment processes.

Dissolved Air Flotation process

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.
Treatment flow with DAF.

*average values that depend on characteristics of the treated flow

Key DAF Features

  • Total suspended solids (TSS) reduction up to 97%
  • Chemical oxygen demand (COD) removal up to 85%
  • Low-cost operation and maintenance (O&M)
  • Standard and customized units meet a variety of application and flow ranges
  • Designed for ease of installation and use
  • Suitable for high-salinity water

DAF Applications

Industrial:

  • Meat/poultry/fish processing
  • Dairy industries food processing
  • Petroleum refineries
  • Pulp and paper plants

Municipal:

  • Water treatment plants
  • Wastewater treatment plants
  • Biological treatment plants — algae removal
  • Fat and oil removal plants

Advantages of RWL Water’s DAF Systems

RWL Water has been developing and continually improving DAF systems for more than 20 years and has successfully implemented installations in a variety of applications. We offer full support by experienced process designers and field personnel during all stages of the project, from preliminary designing through commissioning and operation. Our highly reliable solutions are designed and customized to handle a wide range of influent water quality and flow rate. Our DAF solutions are robust and compact, utilizing the space in an efficient way. They are easy to install, operate, service, and clean, with an optimum price-quality ratio.

Contact us for more information about our dissolved air flotation systems, or to request a quote.