What is dissolved air flotation technology?

 

Author: Mike   Time: January 19, 2026   Introduction: I'm Mike, I've been deeply engaged in the field of wastewater treatment and environmental protection equipment for a long time, with extensive front-line experience. I focus on engineering implementation and operation optimization, sharing practical and applicable industry insights.

 

By Mike

Time: January 19, 2026

Introduction: long-term engaged in the production of wastewater treatment and environmental protection equipment, a wealth of on-site construction experience, focusing on the process ideas/equipment selection/operation points

 

#sewage treatment #wastewater treatment #DAF

 

The so-called Dissolved Air Flotation refers to the dissolution of air in water under pressurized conditions, and then the pressure is suddenly reduced to atmospheric pressure so that the oversaturated air is released in the form of fine bubbles. At present, the commonly used Dissolved Air Flotation mainly has two forms of shallow air flotation and stratified air flotation.

 

 

Conventional Dissolved Air Flotation is done in a pressure vessel tank. Whether the pressure vessel tank is horizontal or vertical, it is through the 1-2 kg pressure difference will be melted into the water (back to the water), is in a static state to complete the process of dissolved air, so the efficiency is quite low, in order to improve this problem, and later the appearance of the Bauer ring improves the efficiency of the efficiency of a little bit, but still can not meet the requirements of high efficiency, and then later appeared in the jet dissolved air, that is, in the air flotation dissolved air tanks inside the installed Venturi

 

Conventional Dissolved Air Flotation in the release before the release of the releaser, there is a shut-off valve to complete the release process, due to the simple structure, so the release of air bubbles than the larger, generally advertised by manufacturers in the 20-50 microns, the actual should be between 50-100 microns; conventional Dissolved Air Flotation due to the addition of the releaser, and its own processing Conventional Dissolved Air Flotation has a general effect, so it is easy to be clogged from time to time, and it needs to be stopped and cleaned up.

 

The traditional container pressure tank has the following disadvantages: low air dissolution rate, about 3%; dissolved air efficiency is affected by the environment, the higher the temperature, the worse the effect; only rely on the pressure difference to complete the static dissolved air process.

 

 

 

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Inclined-flow dynamic separation results in significant hydraulic disturbance and a high bubble breakage rate, leading to the formation of suspended solids that are partially floating and partially settling. Consequently, the effluent contains a high concentration of suspended solids.

 

The separation height is approximately 2,500 mm, with a hydraulic retention time of 30–45 minutes and a surface loading rate of 2–5 m³/(m²·h).

 

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The air dissolution method of shallow air flotation, including MST shallow air flotation, fundamentally departs from the conventional static dissolution approach and instead employs a dynamic air dissolution system.

 

After entering the dissolution tube, the return water is immediately sheared into ultra-thin water layers by the outlet air distribution device. Air is then efficiently dissolved through porous air distribution, significantly enhancing gas–liquid contact efficiency.

 

By applying the zero-speed principle, vertical separation, and a shallow-tank configuration, the effective separation path is limited to approximately 400 mm, with a hydraulic retention time of only 3–5 minutes and a surface loading rate of 5–15 m³/(m²·h).

 

The system is characterized by a compact footprint, high dissolved air efficiency, rapid and thorough separation, and low suspended solids concentration in the effluent.

 

The overhead structural design further improves land utilization efficiency, making shallow air flotation particularly suitable for advanced wastewater treatment applications.

 

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MST Shallow Ion Air Flotation is developed based on conventional horizontal flow DAF systems and Krofta shallow air flotation technology, featuring a disruptive redesign of the dissolved air system structure.

 

It adopts a high-frequency common-rail jet injection strong dissolution and cutting patented technology, enabling dissolved air efficiency to remain unaffected by environmental conditions. The theoretical air dissolution rate reaches the maximum value of approximately 22%.

 

In addition, the release mechanism has been innovatively upgraded with a microbubble generation system, which can alter the surface tension of water molecules, adsorb chromophoric groups, and destabilize certain hydrophilic colloids, thereby significantly enhancing flotation performance.

 

 

The main difference between conventional Dissolved Air Flotation (DAF) systems-including horizontal flow DAF and combined DAF-and shallow air flotation lies in the structure of the tank.

 

Conventional DAF tanks typically have a water depth of about 2–2.5 meters, while shallow air flotation tanks have a depth of approximately 0.6–0.85 meters.

 

There are also differences in the length of the separation process. In conventional DAF systems, water enters at one end and exits at the other. Separation occurs along an inclined upward path, and the separation distance is relatively long. It is also affected by the sludge scraping method; therefore, the separation effect is not very thorough.

 

Shallow air flotation tanks are circular in structure and mainly focus on achieving "zero-velocity" water distribution. The so-called zero velocity is a relative concept. It refers to a condition in which the velocity of the influent water flow is opposite to the backward movement of the traveling bridge. When the two velocities are equal, the water reaches a relative zero-velocity state at the moment it is released.

 

Conventional Dissolved Air Flotation uses a one-cut (full-width) sludge scraping method, which causes significant disturbance to the water body. Shallow air flotation, however, cuts at a single point and lifts the sludge immediately, resulting in very little disturbance to the water body.