Dissolved
air flotation separator is a oil/water separator, which is used for the
removal of suspended solids and emulsified oil from liquids. To remove
the emulsified oil, the emulsion is first broken by the addition of
chemicals. For this, the additional flash mixer and flocculation units
are provided upstream of the dissolved air flotation tank. Flotation of
solids is achieved by the introduction of millions of microscopic
bubbles into the process water. This is attained by drawing a component
of the effluent from the downstream end of the dissolved air flotation
tank and pumping the recycled effluent and atmospheric air to an
adequate pressure saturation vessel / retention tank. The recycled
effluent gets saturated here at an increased pressure in the pressure
tank. The air-saturated stream is then blended with raw wastewater in
the dissolved air flotation tank. When the pressurized flow is restored
to atmospheric pressure in the tank, millions of microscopic bubbles are
released that attach themselves to the suspended particles in the flow
and lift the particles to the surface for effective removal.
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The important components of a dissolved air flotation separator include -
- Oil Skimming Device
- Mixing unit
- Flocculation unit
- DAF tank
- Pressure tank
- Associated equipment, such as pumps, compressors, piping, valves, instrumentation etc.
Dissolved Air Flotation Tank
Dissolved air flotation tanks are designed in both circular as well as rectangular tank configuration configurations. These tanks can be constructed in steel or concrete, which depends on the flow and size. Steel tanks are generally designed for smaller sizes. The rectangular dissolved air flotation tanks can be designed with either separate or integral mixing and flocculation units.
Oil Skimming Device
Oil skimming device is designed at the downstream end of the separator section for disposal and collection of the oil skimmed to the downstream end by the scraper and chain mechanism. The oil skimming devices, which are typically employed for this purpose are the rotatable pipe skimmer, rotary drum skimmer and the floating oil skimmer.
The devices that are generally provided for the mixing and flocculation units include the agitators (mixing unit) and flocculators (flocculation units). The agitators for mixing units are typically vertical motor driven agitator units, which are provided with high efficiency propellers. The flocculators designed for flocculation units are motor driven and can be either vertical or horizontal paddle wheel type depending on the configuration of tank.
Features and Benefits
Some important features and benefits of the modern day dissolved air flotation separators is given below -
- High overflow rate
- Excellent TSS removal
- Small footprint
- Easily handles settled solids
- High float concentration
- Low cost
- Easy to cover
- Excellent oil and grease removal
- Tolerant of large flow changes
- Tolerant of large concentration changes