The pre-treatment AAQUA-DAF (Dissolved Air Flotation) is a widespread technique for the purification of wastewater.
Once the wastewater is filtered, additional oil, grease and suspended solids can be removed with high efficiency by means of an Aaqua-DAF.
The technique of flotation is often combined with a prior physico-chemical treatment, using a coagulant (FeCl3 or PAC) and a flocculant (Polymer). This transforms certain solutes (eg: proteins, heavy metals) into flocs and this technique can also break down emulsions, which increases the efficiency of the oil and grease removal.
Depending on the type of wastewater, COD removal efficiencies between 30 and 95% are achieved.
The AAQUA-DAF is often used:
Suspended solids, fats and oils can be removed using a dissolved air flotation (DAF) unit. The buoancy force of the microscopic air bubbles (20 tot 50 micron) lifts the suspended solids up to the surface. 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 level controller and the motion speed of the skimmer.
The water, supersaturated with dissolved air, is produced in a pressure vessel. The water used in this vessel is recycled from the processed waste water from the effluent compartment.
In certain cases an Aaqua-DAF can be equiped with an additional plate package to obtain a maximum suspended solids removal.
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.
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.
