Dissolved air flotation (DAF) is a water treatment process that uses air bubbles to remove suspended solids like oils, solids, and algae from water. Air is dissolved into the water under pressure, and when this saturated water is released into a tank at atmospheric pressure, fine air bubbles form. These bubbles attach to the suspended particles, decreasing their density and causing them to rise to the surface, where they are then skimmed off.

In a Dissolved Air Flotation (DAF) system, feed water is often treated with a coagulant (e.g. ferric chloride or aluminum sulfate) and/or a flocculant to aggregate fine particles. A portion of the clarified effluent is pressurized and saturated with air in a vessel (air drum), then released into the float tank through a pressure valve. This produces fine air bubbles that attach to suspended particles, lifting them to the surface to form a froth, which is skimmed off. The clear water beneath exits as treated effluent.

Two main configurations exist: circular (more efficient, ~3 min retention time, uses a spiral scoop) and rectangular (longer retention time, 20–30 min).

The Krofta Multifloat DAF units include lamella plates to increase separation efficiency.

CLARIFICATION

Principle:
Uses gravity to settle suspended solids to the bottom.

Process:

• Water enters a clarifier or settling tank.

• Heavier-than-water particles (sludge, sand, grit, flocs) settle down to the bottom.

• Clarified water overflows from the top.

• The settled solids are scraped and removed as sludge.

Typical applications:

• Primary or secondary settling in municipal wastewater treatment.

• Pre-treatment of industrial wastewater with high-density solids.

• Drinking water treatment after coagulation/flocculation.

Advantages:

• Simple and robust.

• Low energy consumption.

Limitations:

• Inefficient for light, slow-settling particles (e.g. oils, algae, or fine colloids).

• Requires large tanks → more footprint.

Principle:

Uses buoyancy from tiny air bubbles to lift suspended solids to the surface.

Process:

• Compressed air is dissolved in water under pressure.

• When pressure is released, microbubbles form.

• The bubbles attach to suspended solids or oils, making them lighter.

• The particles float to the surface, forming a froth layer.

• A skimmer removes the floated sludge.

Typical applications:

• Industrial wastewater (food & beverage, oil & gas, pulp & paper, dairy, brewery).

• Sludge thickening.

• Removal of fats, oils, grease (FOG) and light solids.

Advantages:

• Excellent for light or colloidal particles that don’t settle easily.

• Produces higher-quality effluent in compact footprint.

• Fast separation.

Limitations:

• Higher energy demand (air compressor, pumps).

• Requires chemical dosing (coagulant/flocculant) for optimal performance

Yes, Dissolved Air Flotation is an effective and robust method for removing fats, oils, and grease (FOG) from wastewater. 

It works by injecting fine air bubbles into the water, which attach to FOG particles, causing them to float to the surface for removal by a skimming device. DAF systems can significantly reduce FOG, along with other suspended solids like those contributing to biochemical oxygen demand (BOD). 

Air flotation (specifically DAF: Dissolved Air Flotation) is very good at removing suspended solids (TSS) from water and wastewater.

But how effective it is depends on the type of solids and how well the process is conditioned (coagulation/flocculation, bubble contact, etc.

1. DAF is designed to remove fine, light, or slow-settling suspended solids that don’t settle easily in a clarifier.
Examples include:

• Algae, fibers, oils, greases, colloids, organic fines

• Emulsified solids or low-density particles

• Coagulated or flocculated solids after chemical treatment

These are precisely the types of solids that float when attached to air bubbles.

2. Typical TSS removal efficiency: 

With proper coagulation/flocculation:

• Industrial wastewater: 80–95% TSS removal

• Municipal secondary effluent: 70–90% TSS removal

• Oily or food-processing effluent: often >95% removal

DAF also removes:

• 60–90% of BOD/COD (when solids are organic)

• 80–99% of fats, oils and grease (FOG)

Microbubbles attach to suspended solids and form aggregates that float.

Coagulants neutralize charges and allow colloids to bind.

Flocculants form larger flocs, improving bubble attachment.

Skimmer removes the floated sludge, producing a clear effluent.

The remaining clarified water usually has <20 mg/L TSS, depending on feed concentration.

You need chemicals in air flotation because most suspended particles in water are too small, too stable, and too light to attach effectively to air bubbles on their own:

The Problem: particles are too stable. 

Most particles in wastewater are colloids — microscopic solids (1–10 µm) that:

• Carry electrical surface charges (usually negative).

• Repel each other electrostatically.

• Stay in suspension instead of aggregating or floating.

So if you inject air bubbles directly into raw wastewater, the bubbles won’t stick well to the particles — they’ll just slip past them.

The Solution: chemical conditioning

To make DAF work efficiently, we pre-treat the feed water with:

a. Coagulants

(e.g. ferric chloride, aluminium sulfate, polyaluminium chloride)

• Neutralize the surface charge on particles.

• Destabilize colloids so they can come together.

• Form small, sticky microflocs.

b. Flocculants (polymers)

(e.g. polyacrylamide)

• Bind the microflocs into larger flocs.

• Make them denser and more cohesive.

• Provide a larger surface for bubble attachment.

Result: you get bigger, lighter, more hydrophobic flocs that can easily capture air bubbles and float to the surface.

Krofta DAFs achieve much lower energy and chemical consumption than conventional dissolved air flotation units because of their unique hydraulic design, high efficiency air dissolution, and integrated circular architecture.

Traditional DAFs use a pressurized air tank (air drum) to saturate recycled water with air — often requiring high pressures (4–6 bar) and high recycle ratios (20–50%).

Krofta’s Air Dissolving Tube (ADT) achieves the same or better air saturation at lower pressure (2–3 bar) and lower recycle rate (8–12%), because of:

• Continuous, plug-flow mixing of air and water inside a special tube geometry.

• Perfect air dissolution and no bubble coalescence.

Result:

• Less compressed air needed → lower energy use.

• Smaller recycle flow → smaller pump → less power.

2. Better floc-bubble contact and reduced chemical demand.

Krofta’s hydraulics and microbubble dispersion create:

• Uniform bubble distribution across the flotation zone.

• Controlled, gentle upward velocity of bubbles.

• Extended contact time between bubbles and flocs.

This allows excellent solids capture even with smaller, looser flocs.

Result:

• You can achieve the same separation efficiency with less coagulant and polymer (often 30–50% less).

• Fine-tuning of pH and flocculation is simpler.

3. Integrated design: coagulant, flocculant, flotation all in one compact unit. 

Krofta systems integrate:

• Flocculation chamber (pre-contact zone)

• Air dissolving tube

• Flotation and clarified water collection
  into one compact circular unit.

Result:

• Minimal piping, fewer pumps, fewer dosing points.

• Lower residence time → faster process control.

• Small footprint with high hydraulic loading rates

Renting a flotation (DAF) unit is often a smart, flexible and cost-efficient solution, both technically and financially.

1. No large upfront investment

Buying a DAF system can require hundreds of thousands of euros in capital expenditure (CAPEX).
When you rent, the treatment capacity becomes an operational expense (OPEX) instead.

Benefits:

• No impact on balance sheet or depreciation.

• Immediate access to treatment capacity.

• Ideal for short projects, seasonal production, or emergencies.

Rental DAF units (like Krofta Rental DAFs) are:

• Containerized or skid-mounted

• Fully equipped with pumps, air dissolving system, and controls

• Ready to connect to existing process lines

Benefits:

• Quick installation (often within hours or days).

• No need for civil works or permanent infrastructure.

• Perfect for temporary bypass, pilot, or commissioning phases

If you’re unsure about:

• Effluent variability

• Chemical dosing requirements

• Expected performance

… renting allows you to test real conditions before committing to a permanent system.

Benefits:

• Collect reliable performance data.

• Optimize chemical treatment (coagulant/flocculant).

• Reduce technical and financial risk before investment

Rental DAFs are commonly used for:

• Seasonal production peaks (e.g. brewery, dairy, food industry).

• Temporary non-compliance (e.g. plant upsets, overload).

• Construction or maintenance shutdowns.

• Pilot or remediation projects.

Benefits:

• Stay compliant with discharge limits.

• Avoid production downtime or regulatory penalties.

Rental contracts often include:

• Preventive maintenance

• Remote monitoring

• Chemical and process support

• Option to extend, upgrade, or buy later

Benefits:

• No need for in-house technical expertise.

• Fully supported by the manufacturer.

• Easy to scale up or down depending on flowrate

Renting a Krofta DAF system supports:

• Cash flow optimization — pay only for what you need, when you need it.

• Off-balance-sheet financing — ideal for companies under CAPEX constraints.

• Rapid compliance with environmental regulations.