What is DAF in wastewater treatment?
Dissolved air flotation (DAF) is a process that uses microscopic air bubbles to separate contaminants from water or wastewater. It’s particularly used to treat wastewater by removing suspended solids, oils, and greases. While DAF can be used to recover resources from wastewater or as a polishing stage after biological treatment, it is most commonly used as a pretreatment stage for wastewater treatment across many sectors and industries.
Benefits of Dissolved Air Flotation
DAF has numerous benefits, including:
- Enhanced contaminant removal and regulatory compliance: DAF achieves up to 90% contaminant removal efficiency, offering superior treatment performance and ensuring compliance with environmental regulations.
- Versatility across diverse wastewater streams: DAF effectively treats various wastewater types, from industrial to municipal, addressing a wide range of contamination issues.
- Space-efficient design: With its compact physical footprint, DAF installations maximize space utilization, ideal for facilities with limited land availability.
- Rapid commissioning for agility: DAF systems offer quick commissioning, offering swift adaptability to changing operational needs and immediate response to treatment demands.
- Streamlined sludge management: DAF produces denser sludge than sedimentation methods, leading to less waste volume and easing the sludge handling and disposal process.
- Automation for operational efficiency: DAF systems can be fully automated, enhancing operational efficiency and ensuring consistent, reliable treatment results.
- Continuous and reliable operation: DAF systems maintain continuous and stable operation with minimal input and consistent treatment performance to meet ongoing operational demands.
- Proven technology with wide applicability: DAF represents a well-established technology with broad applicability, offering reliable wastewater treatment solutions across various industries and effectively addressing different treatment challenges.
Image Credit: Mbeychok/CC 3.0.
How Does a Dissolved Air Flotation System Work?
In the DAF process, chemicals are added to the incoming water to promote the formation of flocs from smaller particles, facilitating their removal as these larger aggregates are easier to separate.
The water after flocculation moves to a contact cell (or coagulation chamber), where it is mixed with water into which air has been dissolved under pressure. Upon mixing, the air is released in the form of tiny bubbles that attach to the flocs, aiding in their flotation and removal.
After entering the flotation tank, the flocs, carried by the bubbles, rise to the surface, forming a layer known as “surface float,” or “skimmings” which is skimmed off A separate skimmer also removes any solids that settle at the bottom of the tank.
The clarifier effluent is then separated from the surface float and settled solids using an effluent discharge baffle and chamber, ensuring the removal of containments before the water is discharged.
In the final stage, a saturation system recycles some of the clarified effluent, infusing it with air and reintroducing it to the start of the process, thus maintaining the cycle’s efficiency.
Image Credit: Mbeychok/CC 3.0.
Dissolved Air Flotation Frequently Asked Questions (FAQ)
What is dissolved air flotation particularly good for?
Dissolved air flotation (DAF) effectively clarifies wastewater by targeting suspended substances such as oil, grease, or solids. This process involves dissolving air into water under pressure, which then releases as microbubbles in the water, causing impurities to rise to the surface for removal.
What are some of the applications of DAF?
Oil and Gas Industry: In the oil and gas sector, DAF is utilized to cleanse produced water by eliminating oil, grease, and other contaminants. It’s a common treatment method in refineries and petrochemical plants for purifying wastewater generated from a variety of processes.
Municipal Wastewater Treatment: In municipal wastewater treatment plants, DAF systems are commonly used as a preliminary treatment to remove suspended solids, oils, and other contaminants.
Food and Beverage Industry: In commercial operations such as dairy and food-processing facilities, DAF is used to clarify wastewater and remove solids and organic matter prior to discharge.
Mining: DAF systems assist in the industrial sector as well, such as in the treatment of wastewater generated in mining operations, helping to separate solids and contaminants to ensure clean discharge.
Paper and Pulp: DAF is widely used in paper and pulp operations to remove suspended solids, fibers, and chemical impurities from the wastewater, aiding in the treatment and purification process.
Textile Industry: Textile plants use DAF systems to treat wastewater, focusing on removing color and chemical pollutants.
Energy Sector: DAF is used in power plants to treat cooling tower wastewater and other streams.
Landfills: Landfills use DAF to treat their leachate.
Agriculture: DAF is applied in agriculture to clean runoff and effectively remove sediments, nutrients, and other contaminants.
How efficient is DAF at removing solids?
DAF’s effectiveness in solids removal depends on several factors, including the chemical program used. While micron-sized air bubbles can float larger particles to the surface, a robust chemical program is essential for efficiently removing fine solids and emulsified fats, oils, and greases. Without appropriate chemical treatment, smaller particles are less likely to be effectively removed.
How is algae removed by DAF?
DAF effectively removes algae by making the algae particles buoyant with dissolved air bubbles, causing them to float to the surface. The removal process is similar to that for suspended materials and can be optimized with a well-designed chemical program to improve efficiency.
What chemicals are used in DAF wastewater treatment?
Commonly used chemicals in DAF wastewater treatment include:
- Coagulants: These are used to aggregate fine particles into larger flocs, making them easier to remove during the treatment process.
- Flocculants: These promote the formation of larger and denser flocs, which are easier to float and remove from the water’s surface.
Ferric-based chemistry: These are particularly effective in treating poultry wastewater, as they excel at separating substances like blood from the water.
What is the air-to-solids ratio?
The air-to-solids ratio (A/S) determines the efficiency of the DAF system. It is calculated as the mass of air used per mass of solids in the system. Typical A/S ratio ranges from 0.005 to 0.01, with variations depending on the application. The experts at Seven Seas can help determine the optimal ratio.
DAF Systems With Staying Power
Seven Seas Water Group’s focus on our Water-as-a-Service® (WaaS®) model means we own and operate most of the water and wastewater infrastructure assets we deliver, and we hope that our satisfied customers extend agreements indefinitely.
To make the model work, it is important that we use only the most durable, reliable equipment and components in the industry, and in our quest for quality, we have developed a widespread supplier network. The result is our plants maintain a superior 97% availability rate (the industry standard is 80-85%).
Request a Quote for Dissolved Air Flotation Wastewater Treatment
Contact Seven Seas to explore the possibilities of DAF under financing arrangements that are tailored to your needs. Our experts can work with you to design the right DAF wastewater treatment system for your situation.
Seven Seas Water Group and its affiliates are dedicated to protecting our team members and the environment where we work, live, and operate. See what we’re doing to meet U.N. Sustainable Development Goals and achieve carbon net-zero status.
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