An Introduction to Dissolved Air Flotation

What is it?

Dissolved Air Flotation, or DAF, is a method of wastewater treatment in which dissolved air is released from solution in a flotation tank. The resulting bubbles collect around any materials suspended in the wastewater, floating those materials to the surface where they can be removed by a skimming device.

DAF is particularly useful for industrial wastewater treatment and other applications in which wastewater contains high levels of suspended materials.

How does it work?

Initial wastewater is pumped to the mixer inlet (flocculator), where the wastewater is treated with reagents. Treated effluents enter the mixing chamber of the flotator with a simultaneous supply of a water-air mixture. The air bubbles and waste form flotation complexes that float to the surface.

Larger flotation complexes reach the surface in the mixing chamber, while the rest passes along with the waste water to the flotation chamber, where it is separated from the liquid.

The resulting foam is removed from the surface of the water with a scraper mechanism and discharged into the collection tray. Heavy contaminants settle on the bottom, from where they are removed through a special pipe.

Clarified wastewater is discharged through a controlled overflow into the tank for purified water and removed from the installation. Part of the purified water is taken by the recirculation pump to saturate it with air.

After that, the air-water mixture is distributed for dispersed supply into the flotation and reagent wastewater treatment areas.

DAF’s high performance and removal efficiency prevents materials from passing downstream, preventing the clogging, blockages and abrasion damage that can cause costly downtime or shorten equipment lifetimes.

What contaminants does DAF remove, and at what rate?

Depending on the industry, sector and application, a DAF system can remove the following materials at the following rates:

• COD: 35-80%
• Suspended solids: 85-95%
• Phosphates: 90%
• Sulfides: 99%
• Metals: 95%

What should potential customers look for in a DAF system?

• Low cleaning requirements, or a self-cleaning system. This extends the equipment routine cleaning period.
• Low reagents consumption and improvement of chemical precipitation. Static mixers and smart reagent dosing systems can enable this.
• Safety features. As with any system, things like explosion proofing, foam fire extinguishers, service platforms etc provide enhanced safety.
• A large flotation area. This can be increased through the use of a lamella module or equivalent technology.
• Automated operation, or easy-to-use controls.
• Long-lasting and robust design. Look for systems fabricated from stainless steel or fibre-reinforced polymer.

Summary

A DAF unit could help you to reduce surcharge costs and prevent compliance breaches by discharging treated, environmentally compliant effluent with a high purification efficiency. It can also help to improve operational efficiency with automated processes and low-input, uninterrupted operation.

In industrial environments, time is money and a DAF system can help to prevent downstream damage, blockages and wear through reliable capture of abrasive and clogging materials.