Ovivo® DAF Dissolved Air Flotation

Ovivo® has numerous DAF design options available, including “open end” saturation systems, which are based on sound technical grounds, skid mounted systems and submerged subnatant launder designs. The option of a shallow or tiered system is available where site constraints govern equipment layout. We offer DAF tank covers in steel, aluminum or fiber reinforced plastic (FRP) materials.

Ovivo®Ovivo DAF DAF units are used to remove suspended solids from liquids in industrial and municipal applications. They are especially effective where oils, fats, fibers, greases or colloidal solids are present. In many applications, Ovivo flotator units recover valuable by-products, partially offsetting the operating cost of the plant.

Circular and rectangular configurations are available. Basic operating principles and many advanced design features are described  in the brochure.

  • Sludge thickening
  • Algae removal
  • Clarification
  • Membrane pre-treatment
  • Backwash recovery
  • Clarification
  • Municipal sludge thickening (WAS)
  • Algae removal
  • Oil refinery waste
  • Industrial waste including food and beverage, dairy and meat packing

 

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  • Pressurization systems generate a uniform flow of air bubbles for optimum solids floatation/removal.
  • Single-stage pressurization pump and air compressor methods result in high saturation efficiency.
  • Four skimmer arms ensure efficient removal of floating solids.
  • Constant and variable speed drives are available to control float removal rate.
  • Designs up to 50-ft diameter are standard. Custom sizes are also available.

OCSDistrict submerged launder Picture1Pressurization Systems

Our pressurization units incorporate unique design features into the DAF mechanisms to provide a uniform flow of air bubbles for optimum operation and economy, with the pressurization type and flow rate specifically selected for each individual application. The recycled flow pressurization system developed by Ovivo and used exclusively on all our DAF units, generates 50 to 100 micron-sized air bubbles helping to eliminate detrimental coalescing.

A single-stage pressurization pump and air compressor are used to pressurize a portion of clarified effluent in a saturation tank. As a result of the high saturation efficiency, the cost of pumps, saturation tank, and other pressure system components is reduced. Once saturated with air, the pressurized, clean liquid is returned to the raw waste flow for injection into the flotation unit. A unique back pressure valve is specially designed to maintain the proper pressure in the pressurization tank and to aid in the formation of minute air bubbles.

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Pressurized flow is released in a conical pattern inside the flotation unit, producing thorough mixing with minimal turbulence. Loss of dissolved air through external piping or distribution systems is prevented. The air-water-solids mixture is uniformly distributed across the flotation tank by action of the inlet diffusion chamber.

Dissolving efficiency of the pressurization tank provides 80 percent or greater saturation. The tank is specially designed to reduce the exit velocity of the pressurized recycle flow to ensure that all free air is removed from the liquid prior to leaving the tank. This feature ensures that turbulence caused by large bubbles is reduced and that the micron-sized bubbles form properly. In accordance with Henry’s Law, more air is dissolved into a given volume of water at increased pressures. A 65 psi system requires less recycled water and produces smaller air bubbles than those operated at lower pressures. Recycled water serves to transport dissolved air to the flotation unit. Minimum recycling reduces hydraulic loading and turbulence, increasing the amount of treatable liquid that can be introduced in a given tank, thus reducing the cost capital and operating costs.

Once air has been dissolved in the recycled liquid, the pressurized stream is released into the flotation unit to provide air bubbles to effect flotation. A shearing force occurs as the pressurized stream contacts the treated liquid. Micro-sized air bubbles form by action of the relief valve and diffuser, and then attach to floc particles in the waste stream at the point of pressure release. Maximum solids capture and high quality subnatant is assured when air bubbles form on solids particles by the three methods of air bubble attachment.

 

What technical service is available?
Technical service is available for installation and start-up of new systems.

 

Why use DAF?
Dissolved air flotation is designed for the removal of suspended solids or water immiscible liquids from process or wastewater to produce an effluent of high clarity and free of objectionable particles or liquid. Dissolved air flotation is best applied to remove materials that normally settle slowly, persist by remaining in suspension, or have a tendency to float. Benefits of flotation are rapid process results – flotation happens immediately while sedimentation takes time, higher loading rates than gravity thickening, and fresher sludge / solids.

 

What is a DAF thickener and a DAF clarifier?
For a DAF thickener, solids thickening is the goal. Both solids and hydraulic loading must be considered for proper sizing.
For a DAF clarifier, subnatant clarification is the goal. Hydraulic loading governs and solids loading is usually not a problem. With high volumes of dilute solids, a higher air/solids ratio is used and a recycle rate of 10-30% of the forward flow is selected depending on how “easy to float” the material is.

 

Is there an easy test to tell if a DAF is right for an application?
A simple lab test will generally determine if the use of a DAF is feasible. Further testing can be done to simulate the operation of the DAF under specific operating conditions.

 

Can a DAF be used in a batch process?
Yes, although the DAF operates as a continuous separation device, it can be used in batch processes. In these cases, the unit would be operated intermittently as needed.

 

How is the correct size determined?
Lab or pilot testing is often the best way to determine the correct separation characteristics of a given waste stream. In many cases, a DAF has been previously installed or tested for the same or a similar application. This provides a good starting point in selecting equipment.

 

How does DAF compare to gravity thickeners?
DAF units typically have a smaller footprint when treating the same waste because they can handle greater loading rates. DAF units are typically loaded at 24 – 48 lb/day/sf. Gravity thickeners are usually loaded at 5 – 7 lb/day/sf. DAF units produce a fresher sludge that floats immediately – there is no need to wait for it to settle and compact.
DAF units typically produce 3 – 6% solids concentration from waste activated sludge (WAS), without polymer, compared to 2%+ from gravity thickeners.
What designs are available?
The design of the DAF can be customized to suit specific needs for a given application. Both circular and rectangular units are available. Bottom collectors are used in a DAF to remove any portion of the influent solids that settle rather than float. DAF’s can be constructed of a variety of materials including carbon steel or stainless steel.

 

What other auxiliary equipment is needed?
Generally, chemical pre-treatment tanks with mixers and chemical metering pumps are required. In some cases, feed or effluent pumps are needed as well. Depending on customer needs, dewatering equipment can also be provided. Auxiliary equipment can be provided by for a complete system including controls and instrumentation.

 

What utilities are required?
Electric power is required to run the skimmer, rake drive and the recycle pump. Compressed air is required for the air dissolving system.

 

How much operator attention and maintenance are required?
The DAF is essentially a hands-off mechanism that requires little operator attention. Maintenance usually involves lubrication of drives and bearings and occasional replacement of wear items. Existing units can also benefit from a service visit to assist in optimizing performance. Please contact us for a service proposal.

 

Are pilot units available?
DAF pilot units are available for rental for testing at customer facilities. Please contact us for pilot equipment availability.

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