DISSOLVED AIR FLOTATION

The treatment process is based on chemical coagulation, clarification and rapid sand filtration. This process train is widely accepted and is very applicable to the treatment of coloured and turbid surface waters for municipal and industrial applications.

In the Rawdon Technologies System, the clarification stage employs dissolved air flotation (DAF). DAF is a very efficient, high rate clarification process that has been in use for many years in water and waste-water treatment.

The suspended solid matter in the chemically treated water is separated by introducing a recycle stream containing small bubbles which floats this material to the surface of the tank. This is achieved by recycling a portion of the clarified flow back to the DAF unit. The recycle flow is pumped to higher pressure and is then mixed with compressed air. The flow passes through a tank where the air dissolves to saturation at the higher pressure. When the pressure is released at the clarifier, the dissolved air precipitates as a cloud of micro bubbles which attach to the particulate matter causing it to rise to the surface.

The DAF process is particularly well suited for the removal of floc formed in the treatment of low alkalinity, low turbidity, coloured water. This type of floc tends to be very fragile and voluminous, making traditional gravity sedimentation inefficient. Flotation processes do not require large, heavy floc in order to achieve efficient solids removal. This results in lower chemical dosages and reduced time required for flocculation. The compressive forces applied to the sludge by the buoyant bubble/floc agglomerates result in greatly reduced volumes of waste-water from the clarification process. This enhances the efficiency of chemical use and reduces the volume of residuals to be treated.

An equally important benefit of the technology is the efficiency of the clarification process. Since the performance of the filtration process is directly affected by the amount of solids in the clarified water, thehigh degree of solids removal achieved in the DAF results in an overall increase in system performance. In order to meet the new, stringent standards for turbidity removal in potable water applications, this high performance is essential.

 

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