March 17, 2021
For the removal of grease, dissolved air flotation (DAF) is very suitable, especially in the specific gravity of suspended solids is close to 1.0. For example, wool washing wastewater, Contains up to 12,500 mg/L of oil. The oil exists in a dissolved state (<20 µ) in an emulsified form (Between 20 – 150µ) and free oil (> 150µ).
The DAF process uses compressed air to release microbubbles (10-50 microns Diameter) attached to the particles, making the free oil particles easy to rise to Surface, then skim off. DAF is very effective in removing grease because Oil does not settle naturally, and its specific gravity is less than that of water. When the oil is If it exists in an emulsified form, chemicals are needed to destroy the stability of the oil emulsion layer.
The pressurized water flow can be the entire inflow of wastewater, part of the inlet flow, or Water (waste water) that has been treated in this process. This leads to the three available types of DAF The processes are called full flow, partial flow or recirculation flow (R-DAF). Figure 23 A schematic diagram of the DAF process is shown. The most common application of DAF in wastewater Processing is a circulating flow system because it requires less pressurized equipment (Reduce energy consumption), avoid the problem of pump wear and prevent the formation of the pump Colloids and emulsions in the pump system.
The DAF device can reduce the influent concentration to 10-25 mg/L. Not more than 500 mg/L. Hydraulic load factor ratio of DAF system 5 – 15 m/h gravity sedimentation system, so the residence time is shortened 15-30 minutes. This makes the DAF system more compact and has a smaller footprint. DAF systems are available in circular or rectangular configurations.
The operating parameters important to DAF control are: hydraulic loading rate (HLR), solids
loading rate (SLR) and air to solids ratio (A/S).
HLR is effluent flow divided by the area of the tank and expressed as m/h.
SLR is determined by dividing the solids loading by the surface area of the tank and is expressed as kg/h/m. It is a parameter used to evaluate whether a DAF unit is overloaded or underloaded with respect to solids loading2.
A/S expressed in mL/mg – is the volume of air available / mass of solids to be removed.
