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Reasons for the Ineffective Performance of the Dissolved Air Flotation

Dissolved air flotation (DAF) is a long-established solid-liquid separation technology widely used in water treatment applications globally. Its principle involves introducing a large number of tiny air bubbles into wastewater. Through the interaction of bubbles with particulate matter facilitated by surface tension, including processes such as adsorption, coagulation, and hydrodynamics, the bubbles adhere to suspended particles. This results in an overall specific gravity less than 1, causing them to float to the water surface based on the principle of buoyancy and achieving solid-liquid separation, thereby purifying the wastewater.


Reasons for the poor performance of the DAF unit include:

  1. Wastewater Flow Rate

The impact of wastewater flow rate on treatment effectiveness is significant. During dissolved air flotation machine operation, it is essential to ensure uniform distribution of water to each DAF cell. Changes in flow rate indicate variations in pollutant quantity, requiring timely adjustments to chemical dosing for optimal results. Excessive wastewater flow accelerates the horizontal flow velocity in the DAF cell, reducing residence time, which is unfavorable for the upward flotation and separation of flocs. High flow velocities can lead to excessive turbulence in the separation zone, causing the breakup of bubble-floc aggregates. When water volume is excessive, adjustments to the effluent weir height should be made promptly to prevent wastewater from entering the float sludge system.

  1. Dissolved Air Water Volume, Recycle Ratio, and Dissolved Air Tank Pressure

The turbidity of the source water for dissolved air is crucial, and lower turbidity makes air dissolution easier. The dissolved air water volume and recycle ratio (dissolved air water volume/original water volume) should be determined based on water quality conditions. Higher dissolved air water pressure facilitates the dissolution of oxygen into the water, with the optimal pressure range being 4.0-5.0 kg/cm2. Adjustment of dissolved air tank pressure can be achieved through the dissolved air water outlet valve in the DAF unit. Tightening the valve increases pressure, while loosening it decreases pressure. If the raw water contains an increased amount of floc, the recycle ratio can be adjusted appropriately, but attention should be paid to the pressure of dissolved air water. Simultaneously, the normal working status of the recycle pump should be ensured.

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