dissolved air flotation process (DAF process) is an efficient and fast method for separating solid particles from water and wastewater.

Working principle:

Part of the treated wastewater is circulated into the dissolved air tank. In the state of pressurized air, the air is supersaturated and dissolved, and then mixed with the raw water added with flocculant at the inlet of the air flotation tank. Due to the pressure reduction, the supersaturated air is released. Tiny air bubbles are formed, which quickly attach to the suspended matter, lifting it to the surface of the flotation tank. This forms a sludge floating layer that is easy to remove, and the heavier solids settle at the bottom of the tank and are also removed.

Scope of application:

It is suitable for purifying sewage with high chroma, low dissolved oxygen and many organic impurities. It is especially effective for sewage purification with low water temperature and unsuitable gravity sedimentation. This process is suitable for industrial wastewater treatment and production water treatment after printing and dyeing, electroplating, tanning, papermaking, chemical industry, textile, meat processing, oil refining, canned food, etc. It is also suitable for the separation of biological mud film and water in biological treatment. 

Process flow:

(1) Coagulation part of dosing and dosing mixer:

The sewage is pumped from the sewage tank to the vortex reactor by the sewage pump. Generally, dosing is used before the sewage pump. In this way, the liquid medicine and sewage can be fully mixed through the rotation of the impeller of the sewage pump. The liquid medicine is supplied by the dosing device. The medicated sewage enters the vortex reactor, and the sewage is fully coagulated.

(2) The part of the reflux water-soluble gas releaser:

The quality of the air flotation effect mainly depends on the effect of the reflux water-dissolved air and the release. The air flotation adopts energy-saving dissolved air and release equipment. The compressed air of the air compressor and the reflux water pressurized by the water pump after treatment are fully mixed and dissolved in the dissolved gas tank to form dissolved gas water. The working pressure of the dissolved gas tank is generally 2-3.5kg/cm2.

(3) Air flotation part:

The sewage that is coagulated by adding medicine enters the air flotation tank, and the dissolved air water in the dissolved air tank is suddenly decompressed by the dissolved air releaser at the lower part of the inlet and outlet pipes, so that the air dissolved in the water is suddenly decompressed and a large amount of water is released. Microbubbles. Micro-bubbles encounter the suspended solids in the sewage during the rising process, and the micro-bubbles adhere to the suspended solids and make them float up quickly, so that all the suspended solids treated in the sewage float on the top. Then they are scraped off by the scraper on the upper part of the air flotation and discharged into the sludge tank, and the bottom of the tank is discharged through the treated clean water.

(4) Electrical control part:

This equipment is equipped with an electrical control cabinet, which can reach unmanned operation status after debugging and installation. The electric control cabinet controls the operation of air pumps, foam scrapers, dosing mixers and other equipment.

Process flow and characteristics of dissolved air flotation (Figure 2)

Process features:

1. Under pressurized conditions, the solubility of air is large, and the number of air bubbles used for air flotation is large, which can ensure the air flotation effect;

2. The dissolved gas is suddenly decompressed and released, and the generated bubbles are not only fine, uniform in particle size, high in density, but also floating and stable, and have little disturbance to the liquid, so it is especially suitable for solid-liquid separation of loose flocs and fine particles;

3. The technological process and equipment are relatively simple, which is easy to manage and maintain; especially the partial return type, the treatment effect is remarkable and stable, and the energy consumption can be greatly saved.

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