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DAF flotation equipment operates based on a specific principle to achieve efficient separation of contaminants from water.
Air Dissolution Stage
First, a portion of the treated water is pumped into a pressurized tank, known as the air - saturation tank. In this tank, air is introduced under pressure. The pressure forces the air to dissolve in the water, creating a supersaturated solution of air in water. The solubility of air in water increases with pressure according to Henry's law. For example, when the pressure in the air - saturation tank is set at around 3 - 5 atmospheres, a significant amount of air can be dissolved in the water.
Bubble Generation Stage
After the water is saturated with air, it is then released suddenly into the flotation tank through a pressure - reducing device, such as a special nozzle or a throttling valve. The sudden drop in pressure causes the dissolved air to come out of solution and form numerous tiny bubbles. These bubbles typically range in size from 20 to 100 micrometers in diameter. The small bubble size is crucial as it provides a large surface area for attachment to suspended particles.
Particle - Bubble Attachment Stage
In the flotation tank, the wastewater containing suspended contaminants is introduced. The tiny air bubbles rise slowly through the water column. As they ascend, they come into contact with suspended particles, such as fine - grained solids, oil droplets, or organic matter. Due to the hydrophobic nature of many contaminants, they have an affinity for the air bubbles. Through processes like Van der Waals forces and electrostatic interactions, the particles attach to the surface of the bubbles. For instance, oil droplets, which are non - polar, are attracted to the non - polar surface of the air bubbles and adhere to them.
Separation Stage
Once the particles are attached to the bubbles, the combined particle - bubble aggregates become buoyant. The buoyant force of the bubbles is strong enough to overcome the gravitational force of the particles. As a result, these aggregates float to the water surface quickly. At the surface, they form a foam - like layer, which can be easily skimmed off using mechanical scrapers or other removal devices. The clarified water, now free from most of the contaminants, can be discharged or further treated as required. This entire process of air dissolution, bubble formation, particle - bubble attachment, and separation enables DAF flotation equipment to effectively clean wastewater and separate valuable substances from it.
