Biosludge DAF


In a continuous system the biological treatment plant is continuously fed and the sludge is separated from the waste water in a separate clarifier. It is often so that this clarifier creates a lot of problems such as to light sludge and still too many suspended solids in the effluent. A conventional clarifier is after all a gravity sedimentation tank/settler.

A Biosludge DAF saves a lot of space as well as the investment in a classic clarifier.

Usually a small dose of flocculant (polymer) is added as to improve the flocculation and the separation efficiency. In this way, even with very light sludge, we get a very clear effluent.

Additionally the already obtained flotation sludge already has a solid content of > 4%, so the excess sludge volume has drastically decreased.  The Biosludge DAF is often used :

  • in stead of a clarifier after a continuous aerobic treatment 
  • as a residual phosphate removal step
  • as a sludge separation in "2 stage biological treatments" with sludge separation
  • in aerobic treatment plants with relatively low sedimentation velocity of the biological sludge.
  • for economic reasons and lack of space
  • as a more reliable and efficient sludge separation technique than a conventional clarifier
  • as thickener of excess sludge for the further sludge disposal and sludge treatment 
A biosludge DAF is intended to separate the  flakes of the effluent. This by means of use of "supersaturated water".

The microscopic airbubbles (20 to 50 micron) of the supersaturated water attach to the sludgeflakes like balloons and lift them to the surface of the floatation-unit. The necessary water, supersaturated with dissolved air, is produced in a pressure vessel. The water used in this vessel is recycled from the processed wastewater from the effluentcompartment.

A Biosludge-DAF needs a lot of supersaturated water in order to saturate all the sludge flocs with it.  Proper sizing of the recirculation flow, the size of the saturation vessel and the size of the recirculation pump are therefore of prime importance.

This floating sludge is thickened by means of a sludgethickening grid.  The partly dewatered sludge is then skimmed into the sludge compartment.  A dry solid content of the floatation sludge of 3 to 4% DS is realistic.

The dry solid content of the sludge can be adjusted by a simple levelcontroller and the motionspeed of the skimmer.

A biosludge-DAF is usually equipped with an additional plate pack in the latter part of the DAF so even the smallest flakes can be removed.

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