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 too light sludge and still too many suspended solids in the effluent. To solve this problem the effluent is directed to an Effluent-polishing DAF to obtain further clearance.
To increase the efficiency of COD, phosphate and suspended solids, a physical chemistry can be installed on the effluent of the clarifier, prior to the flotation.
This additional effluent treatment may realise an additional COD removal of 40% on "hard biodegradable water"and reduce phosphate concentrations to <1 mg / l.
Additionally the already obtained flotation sludge already has a solid content of > 4%, so the excess sludge volume has drastically decreased. The effluent-polishing DAF is often used :
An Effluent-Polishing-DAF is intended to remove suspended solids. This by means 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 flotation-unit.
This floating sludge is thickened by means of a sludge-thickening grid.
The partly dewatered sludge is then skimmed into the sludge compartment. The dry solid content of the sludge can be adjusted by a simple levelcontroller and the motionspeed of the skimmer.
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.
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.
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.
The effluent compartment is a standard feature on the AAQUA-DAF Flotation-unit. This compartment can be used to inject neutralizing chemicals for pH correction. If the effleunt has to be pumped, an additional pumppit is not necessary. From this compartment the waste water can be pumped directly for further processing, with dry-mounted pumps or with submerged pumps, mounted in the effluent compartment of the DAF-unit.
