Dissolved Air Flotation

Dissolved Air Flotation

Dissolved Air Flotation(DAF) system is a kind of commonly used solid-liquid separation equipment in the sewage treatment industry, which can effectively remove the suspended matter, grease, rubber substances in the sewage, and is the main equipment of the sewage preliminary treatment.

(I) structural features: the main body of the equipment is rectangular steel structure. The main components are dissolved air pump, air compressor, dissolved air tank, rectangular box, air flotation system, mud scraper system, etc.

1. The air dissolving tank produces small bubbles with a particle size of 20-40um, and adheres to the flocculate firmly, which can achieve good air flotation effect;

2. Less use of flocculant and lower cost;

3. The operation procedures are easy to master, the water quality and quantity are easy to control, and the management is simple.

4. Equipped with back flushing system, the releaser is not easy to block.

(II) working principle: the dissolved water is produced in the dissolved gas tank, and the dissolved water is released to the water to be treated through the releaser under reduced pressure. The air dissolved in the water is released from the water to form 20-40um micro bubbles. The micro bubbles combine with the suspended solids in the sewage to make the proportion of the suspended solids smaller than the water, and gradually float to the water surface to form scum. There is a scraper system on the water surface to scrape the scum into the sludge tank. Clear water enters the clean water tank through the overflow tank at the lower part.

(III) scope of use: 1. It is used to remove the solid suspended matter, oil and various colloidal substances in the sewage, such as the sewage treatment of petrochemical, coal mine, paper making, printing and dyeing, slaughtering, brewing and other industrial enterprises; 2. It is used to recover useful substances, such as the collection of small fibers in the white water of paper making.

What is a DAF ?

Dissolved air flotation (DAF) is a water treatment process that clarifies wastewater by removing suspended solids. The removal is achieved by dissolving air in the water or wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank. The released air forms tiny bubbles which adhere to the suspended matter causing the suspended matter to float to the surface of the water where it is then removed by a skimming device. Chemicals can be added to the feed water to improve solids removal.

Where and Why are DAFs used?

DAFs are widely used in treating industrial wastewater effluents from oil refineries, chemical plants and paper mills to the food & beverage industries. DAFs are used to removed suspended solids, such as Total Suspended Solids (TSS), Fats, Oil & Grease (FOG) and other pollutants from wastewater so that the water is suitable for re-use or discharge to a wastewater treatment facility.

How does a DAF work?


Dissolved Air Flotation


Wastewater is fed into a DAF system and hit with a stream of “whitewater”, which is recirculated clarified water from the DAF that’s super saturated with dissolved air. As these two mixtures blend together, microscopic bubbles attach to solid particulates, giving them enough buoyancy to surface in the DAF tank.

As solids accumulate in a floating layer on the top of the DAF tank, a skimmer gently nudges the sludge toward a discharge hopper.

Any solids that don’t float will sink to the “V” bottom of the DAF tank. Settled solids are concentrated and discharged by an automatically controlled pneumatic drain valve.

The clarified water flows out via an under-over weir on either side of the DAF unit. Some of this water is used in the recirculation loop while the rest flows out of the vessel.

Dissolved Air Flotation


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