Dissolved air flotation with high capacity and efficiency

Dissolved Air Flotation DAF:An Overview of the Technology for Water and Wastewater Treatment
Dissolved Air Flotation(DAF)is a water treatment process that removes suspended solids,oil,grease,and other contaminants from wastewater.
It has been used for decades in various industrial applications,including food processing,mining,paper production,and desalination plants.
In this article we will explore DAF technology which is an effective and reliable,making it one of the most popular methods for wastewater and sewage treatment.
What is Dissolved Air Flotation DAF?
Dissolved air flotation DAF is a process that separates solids and liquids in wastewater by introducing fine bubbles of air into the water.The air bubbles attach to the suspended solids and float them to the surface of the water,where they can be removed.
DAF technology can range from simple circular basins equipped with a configuration of submersible nozzles,which bubble pressurized air up through a near stagnant pool of wastewater,to dynamic systems designed with multiple compartments,which capitalize on different water retention times in each compartment and a combination of settling,flotation,and impingement to remove contaminants.
Dissolved Air Flotation(DAF)System Design
Dissolved Air Flotation(DAF)systems are designed to remove:
Total suspended solids(TSS)
Chemical oxygen demand(COD)
Biochemical oxygen demand(BOD)
Oils and greases(O&G)
Contaminants are removed using a dissolved air-in-water solution produced by injecting air under pressure into a recycle stream of clarified DAF effluent.
This recycle stream is then combined and mixed with incoming wastewater in an internal contact chamber where the dissolved air comes out of the solution in the form of micron-sized bubbles that attach to the contaminants.
The bubbles and contaminants rise to the surface and form a floating bed of material that is removed by a surface skimmer into an internal hopper for further handling.
A first-principles design would involve predicting how much air per kg of water could be dissolved in water at a given temperature and pressure using Henry’s law,then working out the required recycle water flowrate based upon an amount of air per incoming solids load.It is this second factor which cannot be determined from first principles.It can be measured experimentally,or more commonly estimated based on experience.

How does Dissolved Air Flotation DAF Process Work?
The DAF process involves three main steps: 
Coagulation
Flocculation
Flotation
In the coagulation stage,a coagulant is added to the wastewater to destabilize the suspended solids and other contaminants.
In the flocculation stage,a flocculant is added to the water to create larger particles that are easier to remove. 
Finally,in the flotation stage,fine bubbles of air are injected into the water,causing the flocculated particles to float to the surface of the water.The floating particles are then removed by a skimming device.
In the picture below we describe the DAF unit process design:

(A)The effluent enters the flotation tank clarification chamber
(B)Tiny air bubbles are released from diffuser nozzles into this chamber pre effluent entry
(C)These micro-bubbles attach to the solid contaminants or chemical flocculants.This causes the impurities like oil and grease to float to the surface and these are then trapped and removed using a mechanical skimmer
(D1)The skimmer consists of a series of paddles or flights in the flotation tank.These skim just below the surface of the flotation tank removing the floated Sludge containing contaminants into a separate trough for recovery.
The clarified water flows to the bottom of the flotation clarifying chamber and then to an effluent control weir for separation and collection
(D2)The sinking solids are collected in the hopper and these are then removed via a manual or automated valve
(E)The final treated and clarified effluent gets discharged into a sewage drain or for further treatment,as required
Treatment Efficiency of Dissolved Air Flotation(DAF)Units
The treatment efficiency of a Dissolved Air Flotation(DAF)unit can range from 25%to 99%,depending on the specific conditions of the wastewater being treated and the design and operation of the unit.
It is important to carefully evaluate the factors that can affect treatment efficiency when selecting and operating a DAF unit for wastewater treatment.
In the following table we summarize the minimal efficiency of DAF in removing significant pollutants parameters from sewage and wastewater:Parameter

Dissolved Air Flotation(DAF)Pollutants Removal Efficiency
Minimal Removal   Efficiency(
Applications of Dissolved Air Flotation DAF
Dissolved Air Flotation technology is widely used in various industries,including:
Desalination plants
Food and beverage production
Paper and pulp production
Mining and mineral processing
Oil and gas production
Wastewater treatment plants
Dissolved air flotation(DAF)is a commonly used pre-treatment technology in desalination plants.The DAF process removes suspended solids,organic matter,and other contaminants from seawater before it enters the reverse osmosis system for further treatment.
In the food and beverage industry,DAF is used to remove suspended solids,oils,and greases from wastewater generated during food processing.
In the paper and pulp industry,it is used to remove ink and other contaminants from wastewater.
In the mining industry,DAF is used to remove solids from wastewater generated during the extraction and processing of minerals.In the oil and gas industry,it is used to separate oil and water.
For more applications you can get in touch with our team.
Advantages and Benefits of Dissolved Air Flotation DAF
Dissolved Air Flotation (DAF) technology offers several advantages and benefits over other wastewater treatment processes,including:
High removal efficiency:DAF can remove up to 90%of suspended solids and other contaminants from wastewater.
Flexibility:DAF can be used in various applications and can treat a wide range of wastewater types.
Small footprint:DAF systems require less space than other wastewater treatment processes.
No space constraints on industrial sites tend to mean that high-intensity processes like dissolved air flotation(DAF)are favored over low-intensity alternatives such as sedimentation,though design quality is often low in industrial effluent treatment.
More recently, high-intensity DAF has been used to pre-treat seawater to protect against algal blooms prior to its desalination for drinking or industrial water.In this application,surface loadings of 50m/h are common as the algal cells have densities close to or lower than seawater.
An additional advantage of dissolved air flotation(DAF)is that it yields sludge at 5%dry solids content as opposed to approximately 1%dry solids from a settlement tank,which means that sludge pumping and dewatering are cheaper.
A suitable mixed buffer tank is recommended to avoid problems caused by variable sludge solids content on downstream processes and for degassing DAF sludge.
Disadvantages of Dissolved Air Flotation(DAF)
Despite its many advantages,dissolved air flotation(DAF)technology also has some disadvantages, including:
Limited capacity:DAF systems may not be suitable for large-scale wastewater treatment.
Sensitivity to temperature:DAF efficiency can be affected by changes in water temperature.
Chemical requirements:DAF requires the use of chemicals such as coagulants and flocculants,which can be expensive.
Complexity:DAF systems can be complex and require skilled operators.
For high-rate dissolved air flotation(DAF),sludge treatment,and industrial applications,required recycle rates may be several hundred percent of the throughput.Air solubility in water is temperature-dependent,which may also be a factor in selecting a DAF process,since sludges and industrial effluents may be warm,as may seawater used by those countries which desalinate for drinking water treatment.

Sewage Treatment Equipment

Rotary Drumfilter