What is the dissolved air floatation system in wastewater treatment plants? How does it work?

The majority of industrial wastewater is left untreated in India. As a result, the Indian government actively partners with wastewater treatment plant manufacturers to reduce the discharge of untreated waste material in the natural water stream. For example, the Gujarat government’s scheme for financial assistance to the Common Effluent Treatment Plant for the industrial park. Various techniques like screening, sedimentation, flow equalization, biological and chemical treatments, and dissolved air floatation are used to treat water. However, the dissolved air floatation technique is widely used in industries. The NCBI study says that the first DAF systems used in wastewater treatment were Adka and Sveen-Pederson models from the 1920s. The second generation was introduced in the 1960s, followed by the invention of floatation filters at the end of the 1960s. Finally, the development of the third generation was in the 1990s. 

In dissolved air floatation, a specific amount of air is induced in the wastewater using external pressure. Air bubbles adhere to the suspended matter and make sure that suspended matter floats in the water for easy removal.

Advantages of dissolved air floatation (DAF)

• DAF efficiently removes small particles and turbidity.

• It has a short detention time in the flocculation tank.

• It is efficient in removing low-density contaminants formed due to the coagulation of total organic compounds (TOC).

• It leaves a lesser environmental footprint.

• Effectively removes light particles like algae.

• Less sensitive to flow variations.

• Usually achieves lower effluent turbidity (less than 0.5 NTU).

• Because of air bubbles in DAF, it does not require a polymer.

• As it requires lower coagulant dosages, it reduces the sludge volume.

• It also performs better with cold water.

• Its strengthened plastic parts eliminate corrosion.

• Easy to use for recovery and recycling of non-emulsified oils.

• Fully automated DAF systems reduce manual operation.

• Multiple dissolved air floatation units can be installed parallelly for better efficiency.

• It has a rapid start-up time of about 30 minutes.

• Modular designs of dissolved air floatation are easy to set up.

Industries that use DAF for their wastewater treatment

For proficient results, various industries like paper mills, meat, personal care products, seafood, brewery, winery, soft drinks, baking and confectionery, packing manufacturers, cosmetic, dairy, fish processing, petrochemical, pharmaceutical, and textile industries choose the dissolved air floatation technique in wastewater treatment systems.

What are the types of dissolved air floatation techniques?

• Vacuum floatation

In vacuum floatation, the air dissolved in water under atmospheric pressure is released by reducing the surface pressure. Vacuum floatation has been valuable for many years in the pulp and paper industries for the recovery and concentration of fibers.

• Microfloatation

In micro floatation, the air bubble size is minimized to 10-80 µm, and other advancements of micro floatation are lower pressure operation, smaller footprints, and less energy consumption.

• Pressure floatation

The air is dissolved under high pressure and released at atmospheric pressure through a nozzle in pressure floatation. Pressure floatation has received greater acceptance than any other method due to the massive pressure drop available and a significant advantage in expense.

How dissolved air floatation system works in wastewater treatment?

• In the dissolved air floatation treatment, firstly, the wastewater enters the floatation tank. 

• Then tiny air bubbles are introduced into the wastewater through diffuser nozzles. Here, the size of bubbles plays a critical role because large bubbles may cause turbulence in the floatation tank. The optimum size for air bubbles in DAF is 50-100 µm.

• The microbubbles attach themselves to chemical flocculents or suspended solid contaminants. Due to this, pollutants like oil and grease floats to the surface. A mechanical skimmer containing a series of paddles removes the floating impurities.

• Finally, the sinking solids are removed through a valve, and the clear water is collected from the bottom of the floatation tank.

Wastewater treatment plant manufacturers consider dissolved air floatation an ideal treatment for raw water with light particles, drinking water, and seawater desalination. DAF is also a standard treatment to remove matters like oil and grease. However, with stringent effluent discharge limits by CBCP, it is essential to choose a trustworthy wastewater treatment plant manufacturer.