Dissolved Air Flotation (DAF) System in Textile Wastewater Treatment?

The Dissolved Air Flotation (DAF) system is a physicochemical process used to remove suspended solids, oils, greases, and colloidal particles from wastewater. In textile wastewater treatment, DAF is often employed as a pretreatment or intermediate step to enhance the efficiency of downstream processes by reducing pollutant load.

Key Components

1. Pressure Tank: Dissolves air into water under high pressure.

2. Flotation Tank: Releases pressurized water, creating microbubbles that attach to particles.

3. Skimmer Mechanism: Removes floated sludge from the surface.

4. Clarified Water Outlet: Discharges treated water for further processing.

Process in Textile Applications

1. Coagulation/Flocculation:

   • Textile wastewater often contains dyes, surfactants, and organic compounds. Cationic coagulants (e.g., alum, polyaluminum chloride) neutralize anionic dyes and form flocs.

   • Polymers may be added to aggregate fine particles into larger, buoyant flocs.

2. DAF Operation:

   • Pressurized water saturated with air is injected into the flotation tank.

   • Microbubbles (20–50 µm) attach to flocs, lifting them to the surface.

   • Skimmers remove the floating sludge layer, while clarified water exits below.

Advantages in Textile Wastewater

• Efficiency: Removes 60–80% of suspended solids (TSS) and 30–50% of COD/BOD, depending on pretreatment.

• Footprint: Compact design compared to sedimentation tanks.

• Flexibility: Handles variable influent quality (common in batch dyeing processes).

• Speed: Faster separation than gravity-based methods, especially for low-density particles.

Challenges

• Chemical Dependency: Requires precise coagulant dosing for optimal floc formation.

• Foam Formation: Surfactants in wastewater may cause excessive foaming.

• Sludge Management: Generated sludge (3–5% solids) needs dewatering/disposal.

• Operational Costs: Energy for pressurization and chemical expenses.

Case Study Insights

• A textile mill in India reported 70% TSS and 40% COD removal using DAF after coagulation with polyaluminum chloride.

• Another study showed improved color removal when DAF was combined with advanced oxidation (e.g., ozone).

Integration with Broader Treatment

DAF is typically part of a multi-stage system:

1. Pretreatment: Screening, equalization.

2. Primary Treatment: Coagulation/DAF.

3. Secondary Treatment: Biological processes (e.g., activated sludge).

4. Tertiary Treatment: Filtration, membrane processes, or advanced oxidation for residual dyes

What is dissolved air flotation (DAF)?

Dissolved Air Flotation System with the purpose to reduce and remove or low down the COD, TSS and FOG from industrial wastewater.  The DAF system utilises fine air bubbles, also known as ‘White Water’, which attach themselves to the suspended material within the waste stream, increasing buoyancy and floating them to the surface. The floated solids are then removed by a simple but effective scraper mechanism. More often than not chemical conditioning is used to increase the effectiveness of the Dissolved Air Flotation process.

DAF is used in municipal wastewater treatment, industrial wastewater treatment, In these treatment systems, DAF is used to remove a diverse range of pollutants as listed in Table 1. These include suspended solids, organic matter, hydrocarbons from the oil and gas industry, phosphorus and nitrogen from the food and beverage industry, and minerals and metals from the mining industry.

Dissolved air flotation DAF System

How does a dissolved air flotation system work?

In a DAF system, compressed air is pumped into the flocculation chamber of the wastewater system and the compressed air is released at atmospheric pressure. The released air forms tiny bubbles that adhere to the suspended matter. The air bubble-suspended matter floats to the surface of the water (called the floc) and can be removed by a skimming device.

Coagulantor flocculants are added to allow suspended solids and colloidal solids to clump together for their removal by the DAF system. Polyelectrolyte or polymers could be included in situations of reduced performance of the DAF system if the floc is fragile and cannot be removed entirely by skimming.

Coagulants include alum, poly aluminum chloride, poly aluminum sulfate, ferric chloride, bentonite, and organic polymers. The use of these chemicals depend on what needs to be removed. For example, a study showed that monomeric aluminum was more efficient in removing suspended solids and soluble chemical oxygen demand (COD) than polymeric or colloidal aluminum. However, polymeric or colloidal aluminum were more effective in removing soluble silica.

The DAF System Advantages:

• Light particles such as algae that are difficult to settle can be removed by DAF.
• DAF treatment can remove light particles of low concentrations unlike sedimentation that requires a higher concentration of particles to settle for their removal. DAF treatment can be operated using much higher surface loading rates (SLR) than sedimentation.
• DAF treatment leads to clarified water by removing pollutants to assist the water in meeting regulatory standards and depending on the wastewater treatment system, for safe discharge of the treated water into the water bodies.
• Chemical oxygen demand (COD) and biological oxygen demand (BOD) removal.
• Helps drinking water achieve clarity and contributes to preventing issues related to taste, odor, and the possible formation of disinfection byproducts during the water treatment.

What is dissolved air flotation (DAF)?

Dissolved Air Flotation System with the purpose to reduce and remove or low down the COD, TSS and FOG from industrial wastewater.  The DAF system utilises fine air bubbles, also known as ‘White Water’, which attach themselves to the suspended material within the waste stream, increasing buoyancy and floating them to the surface. The floated solids are then removed by a simple but effective scraper mechanism. More often than not chemical conditioning is used to increase the effectiveness of the Dissolved Air Flotation process.

DAF is used in municipal wastewater treatment, industrial wastewater treatment, In these treatment systems, DAF is used to remove a diverse range of pollutants as listed in Table 1. These include suspended solids, organic matter, hydrocarbons from the oil and gas industry, phosphorus and nitrogen from the food and beverage industry, and minerals and metals from the mining industry.

How does a dissolved air flotation system work?

In a DAF system, compressed air is pumped into the flocculation chamber of the wastewater system and the compressed air is released at atmospheric pressure. The released air forms tiny bubbles that adhere to the suspended matter. The air bubble-suspended matter floats to the surface of the water (called the floc) and can be removed by a skimming device.

Coagulantor flocculants are added to allow suspended solids and colloidal solids to clump together for their removal by the DAF system. Polyelectrolyte or polymers could be included in situations of reduced performance of the DAF system if the floc is fragile and cannot be removed entirely by skimming.

Coagulants include alum, poly aluminum chloride, poly aluminum sulfate, ferric chloride, bentonite, and organic polymers. The use of these chemicals depend on what needs to be removed. For example, a study showed that monomeric aluminum was more efficient in removing suspended solids and soluble chemical oxygen demand (COD) than polymeric or colloidal aluminum. However, polymeric or colloidal aluminum were more effective in removing soluble silica.

The DAF System Advantages:

• Light particles such as algae that are difficult to settle can be removed by DAF.
• DAF treatment can remove light particles of low concentrations unlike sedimentation that requires a higher concentration of particles to settle for their removal. DAF treatment can be operated using much higher surface loading rates (SLR) than sedimentation.
• DAF treatment leads to clarified water by removing pollutants to assist the water in meeting regulatory standards and depending on the wastewater treatment system, for safe discharge of the treated water into the water bodies.
• Chemical oxygen demand (COD) and biological oxygen demand (BOD) removal.
• Helps drinking water achieve clarity and contributes to preventing issues related to taste, odor, and the possible formation of disinfection byproducts during the water treatment.

What is dissolved air flotation (DAF)?

Dissolved Air Flotation System with the purpose to reduce and remove or low down the COD, TSS and FOG from industrial wastewater.  The DAF system utilises fine air bubbles, also known as ‘White Water’, which attach themselves to the suspended material within the waste stream, increasing buoyancy and floating them to the surface. The floated solids are then removed by a simple but effective scraper mechanism. More often than not chemical conditioning is used to increase the effectiveness of the Dissolved Air Flotation process.

DAF is used in municipal wastewater treatment, industrial wastewater treatment, In these treatment systems, DAF is used to remove a diverse range of pollutants as listed in Table 1. These include suspended solids, organic matter, hydrocarbons from the oil and gas industry, phosphorus and nitrogen from the food and beverage industry, and minerals and metals from the mining industry.

How does a dissolved air flotation system work?

In a DAF system, compressed air is pumped into the flocculation chamber of the wastewater system and the compressed air is released at atmospheric pressure. The released air forms tiny bubbles that adhere to the suspended matter. The air bubble-suspended matter floats to the surface of the water (called the floc) and can be removed by a skimming device.

Coagulantor flocculants are added to allow suspended solids and colloidal solids to clump together for their removal by the DAF system. Polyelectrolyte or polymers could be included in situations of reduced performance of the DAF system if the floc is fragile and cannot be removed entirely by skimming.

Coagulants include alum, poly aluminum chloride, poly aluminum sulfate, ferric chloride, bentonite, and organic polymers. The use of these chemicals depend on what needs to be removed. For example, a study showed that monomeric aluminum was more efficient in removing suspended solids and soluble chemical oxygen demand (COD) than polymeric or colloidal aluminum. However, polymeric or colloidal aluminum were more effective in removing soluble silica.

The DAF System Advantages:

• Light particles such as algae that are difficult to settle can be removed by DAF.
• DAF treatment can remove light particles of low concentrations unlike sedimentation that requires a higher concentration of particles to settle for their removal. DAF treatment can be operated using much higher surface loading rates (SLR) than sedimentation.
• DAF treatment leads to clarified water by removing pollutants to assist the water in meeting regulatory standards and depending on the wastewater treatment system, for safe discharge of the treated water into the water bodies.
• Chemical oxygen demand (COD) and biological oxygen demand (BOD) removal.
• Helps drinking water achieve clarity and contributes to preventing issues related to taste, odor, and the possible formation of disinfection byproducts during the water treatment.

What is dissolved air flotation (DAF)?

Dissolved Air Flotation System with the purpose to reduce and remove or low down the COD, TSS and FOG from industrial wastewater.  The DAF system utilises fine air bubbles, also known as ‘White Water’, which attach themselves to the suspended material within the waste stream, increasing buoyancy and floating them to the surface. The floated solids are then removed by a simple but effective scraper mechanism. More often than not chemical conditioning is used to increase the effectiveness of the Dissolved Air Flotation process.

DAF is used in municipal wastewater treatment, industrial wastewater treatment, In these treatment systems, DAF is used to remove a diverse range of pollutants as listed in Table 1. These include suspended solids, organic matter, hydrocarbons from the oil and gas industry, phosphorus and nitrogen from the food and beverage industry, and minerals and metals from the mining industry.

How does a dissolved air flotation system work?

In a DAF system, compressed air is pumped into the flocculation chamber of the wastewater system and the compressed air is released at atmospheric pressure. The released air forms tiny bubbles that adhere to the suspended matter. The air bubble-suspended matter floats to the surface of the water (called the floc) and can be removed by a skimming device.

Coagulantor flocculants are added to allow suspended solids and colloidal solids to clump together for their removal by the DAF system. Polyelectrolyte or polymers could be included in situations of reduced performance of the DAF system if the floc is fragile and cannot be removed entirely by skimming.

Coagulants include alum, poly aluminum chloride, poly aluminum sulfate, ferric chloride, bentonite, and organic polymers. The use of these chemicals depend on what needs to be removed. For example, a study showed that monomeric aluminum was more efficient in removing suspended solids and soluble chemical oxygen demand (COD) than polymeric or colloidal aluminum. However, polymeric or colloidal aluminum were more effective in removing soluble silica.

The DAF System Advantages:

• Light particles such as algae that are difficult to settle can be removed by DAF.
• DAF treatment can remove light particles of low concentrations unlike sedimentation that requires a higher concentration of particles to settle for their removal. DAF treatment can be operated using much higher surface loading rates (SLR) than sedimentation.
• DAF treatment leads to clarified water by removing pollutants to assist the water in meeting regulatory standards and depending on the wastewater treatment system, for safe discharge of the treated water into the water bodies.
• Chemical oxygen demand (COD) and biological oxygen demand (BOD) removal.
• Helps drinking water achieve clarity and contributes to preventing issues related to taste, odor, and the possible formation of disinfection byproducts during the water treatment.