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 :
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.
In the pressure vessel of an AAQUA-DAF an air-water mixture is created at a pressure of approximately 5 to 6 bar to produce the "white water".
This supersaturated water is then injected into the flotation-unit trough injection nozzles. With the depressurisation "white water " is created.
This "white water" is saturated with tiny bubbles of only +/- 50 micron. Those bubbles adhere on the surface of the flocs. This way the flocs are moving upwards in the DAF unit.
The supersaturated water, which is so important for good flotation, is continuously produced by circulating a part of the purified water (from 20% to 100%).
A centrifugal pump pumps this partial flow back to a pressure vessel and ensures an optimum pressure for the solution of air in water.
The sludge-thickening grid is important to get a very dry sludge. By dewatering the sludge, the amount of floating sludge to be skimmed, can be strongly reduced. We obtain a sludge with a high dry solid content but wich is still pumpable.
Only the most dewatered sludge on the upper surface is skimmed toward the sludge compartment.
The sludge skimmer is composed of specially profiled flights, fixed onto two stainless steel chains.
The adjustable time controller makes it possible to get a consistent floating sludge.
The flights are equipped with flexible tops.
The sludge compartment is also a standard feature on the AAQUA-DAF Flotation-unit. This compartiment is provided with highly inclinated walls to guide the sludge easily into the suction pipe of the sludge pump.
From this compartment the sludge can be pumped directly into a sludge tank or a sludge thickening-unit.
A laser-level or a hydrostatic level probe on the sludge compartment controls the sludge pump.
Thanks to the laminar flow between the plates the use of an additional platepack can achieve a large reduction of the suspended solids in the processed waste water.
The plate pack increases the effective area of the DAF unit or the settler. The installations are much more compact this way. For the same flows the net floor surface is much lower.
