Dissolved Air Flotation

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Dissolved Air Flotation (DAF) is a process utilized in wastewater treatment for the removal of fine suspended material from an aqueous suspension. The term "flotation" indicates something that floats on or at the surface of a liquid.

The DAF system provides the energy for effective flotation in the form of extremely fine air bubbles, which attach themselves to the suspended material to be removed. This attachment reduces the density of the particle, resulting in increased buoyancy and thus facilitating flotation. Chemical conditioning is often employed to enhance the effectiveness of the dissolved air flotation process.

The most reliable method for producing bubbles of the proper size within a DAF system is to dissolve air into water under pressure and then reduce the pressure of the solution. As the pressure decreases, the air comes out of solution in the form of micro bubbles.

Our Dissolved Air Flotation Clarifier is designed to handle wastewater streams that contain solids, oils, and greases, which are challenging to settle or have a tendency to float. With appropriate chemical conditioning, we effectively remove colloidal and emulsified materials. Complete pretreatment systems can be supplied to ensure optimal performance.

Key features of our DAF system include:

- High rate design

- High removal efficiency

- Compliance with effluent discharge requirements

- Recovery of suspended material

- Reclaiming water for reuse

- Thickening of slurries and sludges

The Drop-X Dissolved Air Flotation Clarifier is specifically engineered for the removal of suspended solids or water immiscible liquids from process or wastewater, producing an effluent of high clarity that is free of objectionable particles or liquids. Dissolved air flotation is particularly effective for removing materials that typically settle slowly, remain suspended, or tend to float.

DAF APPLICATION

Applications of the DAF system include:

- Clarification of a wastewater stream

- Reduction of TSS, COD, and BOD to meet effluent discharge limits

- Recovery of suspended material

- Reclaiming water for reuse

- Thickening of slurries and sludges

Design Parameters

Several key design parameters are commonly applied when assessing the design of a DAF system. The parameters listed below are accompanied by design figures where applicable.

Air : Solids Ratio

The Air : Solids (A:S) ratio may be reported as a volume:mass ratio or a mass:mass ratio and will be specific to each application. Typical values for A:S ratios range between 0.005 - 0.06 ml/mg, which, at 20°C and atmospheric pressure (approximately 1.0133 bar), translates to 0.006 mg - 0.072 mg of air per mg of solids to be removed.

Hydraulic Loading Rate

The hydraulic loading rate in a DAF system measures the volume of effluent applied per unit effective surface area per unit time.

Typical Solids Loadings

Typical figures range from around 2 kg/m².h up to 15 kg/m².h, although the design will be application-specific based on the nature of the solids to be removed and the extent to which chemical aids are utilized.

Recycle Ratio

The recycle ratio can vary significantly, with typical rates being 15-50% for wastewater treatment applications. However, for activated sludge flotation thickening, recycle rates of up to 150-200% have been observed.

Saturation of Effluent

The production of saturated water from which micro-bubbles are generated is typically achieved in two ways. The first method, common in potable water treatment, involves passing the required flow of treated effluent through a packed bed system that is pressurized using a centrifugal pump. In systems where solids are likely to be encountered, such as sludge treatment, the saturation vessel is often kept empty to avoid fouling of packing materials. The percentage of saturation that can be achieved is dependent on system design, but with proper engineering, saturation efficiencies of up to 80-95% can be expected.

Flow Regime

To ensure that DAF systems operate as intended, it is crucial to avoid sudden changes in the flow regime. For this reason, some form of flow balancing or regulation is recommended to maintain a consistent flow rate.