Dissolved Air Flotation: How It Works and Its Benefits in Wastewater Treatment
In many industrial sectors, especially Food & Beverage, rendering, oleochemical, slaughterhouse, and textile, the generated wastewater contains:
- High oil & grease (O&G)
- Suspended solids (TSS)
- Intense color
- Chemical emulsions
- Surfactants that are difficult to separate
These components make conventional sedimentation unable to separate contaminants quickly. When this type of wastewater enters the biological stage, the system may become overloaded because bacteria must work much harder. This is where Dissolved Air Flotation (DAF) becomes a solution capable of significantly reducing the load as a pretreatment process before the subsequent stages.
Why Conventional Sedimentation Is Not Enough
In principle, sedimentation relies on gravity to sink solids to the bottom of the tank. However, in oily wastewater or wastewater with lightweight particles, solids:
- Do not sink
- Float
- Form emulsion layers
- Or become trapped in oil, making separation difficult
This means that this type of wastewater requires the opposite approach of sedimentation: instead of sinking, it must be lifted (flotation). And that is the core of DAF technology.
Working Principle of Dissolved Air Flotation (DAF)
DAF works by utilizing micro-sized air bubbles (microbubbles), which are very small in size and can attach to particles such as:
- Oil
- Fat
- Suspended solids
- Coagulation flocs
These air bubbles create upward buoyancy so that contaminants are “lifted” to the surface and form a flotation layer (scum). The smaller the bubbles, the more effective the lifting process.
DAF Process Stages from Inlet to Sludge Disposal
- Inlet & Conditioning: Wastewater enters the DAF after being treated with coagulation-flocculation chemicals to enlarge the separable particles.
- Pressurization (Saturator): A portion of the water is recycled and depressurized to dissolve air into the water.
- Release & Bubble Formation: When pressure is released, microbubbles are formed and immediately attach to contaminants.
- Flotation Zone: Bubbles carry particles to the surface, forming a thick layer of solids and oil.
- Skimming & Sludge Removal: An automatic scraper removes this layer toward the sludge box.
- Clarified Water: Clear water at the bottom is discharged to the filtration or biological process.
This workflow allows DAF to handle high TSS loads in just minutes.
5. Factors Determining DAF Performance
To ensure optimal DAF performance, several technical factors must be considered:
- Microbubble Size: Smaller → larger contact surface → more effective flotation.
- Saturator Pressure: Typically 4-6 bar; below this, microbubbles are not optimal.
- Coagulation-Flocculation Quality: DAF heavily depends on effective floc formation.
- Recycle Flow Ratio: Typically 10-30% of the total flow.
- Chamber Design: Affects laminar flow and hydraulic retention time (HRT).
Failure in one of these factors can drastically reduce DAF performance.
6. DAF Compared to Other Separation Technologies
| Technology | Suitable For | Weakness |
| Sedimentation | Heavy particles | Not effective for oil & lightweight particles |
| Oil Trap | Free oil | Cannot handle emulsions & surfactants |
| Filter | Low TSS | Easily clogged by oil & grease |
| DAF | High TSS, oil, emulsions | Requires chemical support |
DAF is the highest-efficiency pretreatment method for oily industrial wastewater.
7. Examples of DAF Applications in Various Industries
- Food & Beverage Industry: Effectively reduces oil and grease by 80-95%.
- Slaughterhouse: Removes animal fat & protein residues, drastically reducing biological load.
- Textile Industry: Removes color, chemical flocs, and surfactants.
- Palm Oil Industry: DAF is used to separate oil losses in wastewater.
These applications show that DAF is not only about TSS separation, but also energy efficiency and stable downstream processing.
- Operational Estimation & Maintenance
DAF is categorized as equipment with moderate energy consumption, but highly efficient in separation results. Things to pay attention to:
- Regular cleaning of nozzles & diffusers
- Control of chemical dosage
- Maintaining stable saturator pressure
- Monitoring sludge consistency
- Checking skimmer cycles
With proper maintenance, DAF can operate stably for many years. DAF is a crucial technology for industries with high oil, grease, and TSS content. With the advantages of microbubbles and fast flotation, DAF significantly reduces system burden and keeps biological processes stable. Need a DAF solution? PJL Enviro provides end-to-end solutions tailored to your industrial needs.
