DAF (Dissolved Air Flotation) Systems
Dissolved Air Flotation System for Industrial Wastewater
DAF system for industrial wastewater pretreatment and solids separation. Review process position, wastewater data, chemical treatment and selection requirements.
How a DAF System Works
A dissolved air flotation system separates suspended and floatable material by introducing fine air bubbles into conditioned wastewater. The bubbles attach to floc, oil droplets and suspended solids, reducing their apparent density and carrying them to the surface for mechanical skimming.
In most industrial applications, flotation performance is closely linked to the upstream chemical treatment. pH adjustment, coagulant selection, polymer dosage and floc formation all affect what eventually reaches the flotation zone.
For this reason, a DAF unit should not be selected only from wastewater flow. The hydraulic load, solids load, oil and grease concentration, chemical program and required effluent quality all need to be considered.
Industrial Wastewater Applications
DAF is commonly considered where gravity settling is difficult or where wastewater contains light suspended solids, emulsified or free oils, fats, grease, or chemically formed floc.
Typical industrial applications include:
- food and beverage wastewater
- meat and poultry processing
- dairy processing
- edible oil and food-oil wastewater
- textile and dyeing wastewater
- pulp and paper wastewater
- chemical and manufacturing effluent
- pretreatment before biological wastewater treatment
- pretreatment before filtration or reuse systems
The role of DAF is different from project to project. In some plants it is mainly an oil and solids-removal stage. In others it reduces the load entering biological treatment. It may also be used after biological treatment where flotation is more suitable than gravity clarification.
Where DAF Fits in an Industrial Wastewater Treatment Train
A DAF unit should not be selected as an isolated piece of equipment. Its position depends on the form of the pollutants and the downstream treatment objective.
A typical industrial treatment sequence may be:
Equalization → pH adjustment → coagulation / flocculation → DAF → biological treatment → tertiary treatment
The exact arrangement depends on the wastewater and discharge or reuse target.
DAF Before Biological Treatment
Before biological treatment, DAF can remove suspended solids, fats, oils, grease and chemically formed floc that would otherwise increase the load on the biological stage.
This can be particularly important where the incoming wastewater contains high concentrations of floatable solids or process oils.
The biological process should still be selected from the wastewater that actually leaves the DAF—not simply from the raw wastewater flow.
DAF After Biological Treatment
DAF can also be considered downstream of biological treatment when biomass or fine suspended solids do not separate effectively by gravity.
Whether flotation is appropriate depends on sludge characteristics, solids loading, chemical conditioning requirements and the quality required from the clarified effluent.
For projects involving reuse or more stringent discharge limits, the DAF effluent may then proceed to filtration, membranes, disinfection or other tertiary processes.
Handling the Floated Sludge
The floated sludge is part of the DAF design—not a separate problem to be considered after equipment selection.
The project should review:
- expected sludge production
- approximate sludge concentration
- sludge storage requirements
- pumping arrangement
- polymer conditioning
- operating hours
- final dewatering requirement
- filtrate or centrate return point
- final cake disposal route
A typical sludge line may be:
DAF floated sludge → sludge storage / thickening → conditioning → dewatering → cake handling
For some projects, a screw press, belt filter press, chamber filter press or another dewatering method may be suitable. Selection should be based on sludge characteristics and required cake condition.
Information Required for DAF Selection
A useful DAF quotation requires more than one design flow number.
For preliminary selection, please provide as much of the following information as possible:
Hydraulic data
- average flow, m³/h
- peak flow, m³/h
- operating hours per day
- batch discharge conditions, if applicable
Wastewater characteristics
- TSS
- COD
- BOD, if available
- oil and grease
- pH
- temperature
- salinity or conductivity where relevant
- other important industrial contaminants
Chemical treatment
- existing coagulant, if any
- polymer type, if known
- current dosage
- pH adjustment requirement
- jar-test or pilot-test results, if available
Project objective
- pretreatment before biological treatment
- final solids separation
- reuse pretreatment
- required discharge target
- downstream biological or tertiary process
Sludge handling
- expected sludge volume
- sludge storage arrangement
- existing dewatering equipment
- required final sludge condition
When these data are available, the DAF can be evaluated around both hydraulic capacity and solids-separation duty.
DAF System Configuration Options
The final equipment configuration should follow the process requirement rather than a fixed catalogue layout.
Depending on the project, the DAF scope may include:
- coagulation and flocculation tanks
- chemical dosing equipment
- flotation tank
- recycle pump
- air-dissolving system
- pressure-release arrangement
- surface skimmer
- sludge hopper or collection zone
- control panel
- access platform
- sludge transfer equipment
Chemical preparation and dosing can also be coordinated with the DAF package where required.
HydroNovus already has a live polymer preparation page, so如果你愿意增加第三条内链，可以把：
Frequently Asked Questions
What information is most important for DAF sizing?
Flow is only the starting point. TSS, oil and grease, chemical treatment, solids loading, peak flow and the required effluent quality are also important for preliminary selection.
Does every DAF system require coagulation and flocculation?
Not necessarily. It depends on the wastewater and the pollutants to be removed. However, many industrial wastewater applications use pH adjustment, coagulation and/or polymer conditioning to improve separation.
Can DAF be installed before an MBBR system?
Yes, when pretreatment is required to reduce suspended solids, oils, grease or chemically removable contaminants before biological treatment. The actual process sequence should be based on the wastewater analysis and biological treatment objective.
Can DAF be used after biological treatment?
It can be considered for biomass or fine-solids separation where flotation is more appropriate than gravity settling. Sludge characteristics and downstream water-quality requirements should be evaluated.
What happens to DAF sludge?
Floated sludge normally requires collection, storage and further handling. Depending on its concentration and characteristics, it may require conditioning, thickening and mechanical dewatering before disposal or further treatment.
Can HydroNovus supply the complete DAF pretreatment package?
The project scope can be configured around the required process and may include chemical preparation, coagulation/flocculation, DAF equipment, controls and related sludge-handling equipment. Final scope should be confirmed from the wastewater data and project requirements.
Request a Preliminary DAF Configuration
Selecting a DAF system from flow rate alone often produces an incomplete quotation.
For a preliminary engineering review, send your wastewater analysis and flow profile to HydroNovus.
Please include:
- average and peak flow
- TSS
- COD
- oil and grease
- pH
- operating hours
- current chemical treatment, if any
- discharge or reuse target
- downstream treatment process
With this information, we can review the DAF position in the treatment train, preliminary equipment configuration and the information still required before final selection.