Dissolved Air Flotation Units in Oily Wastewater Treatment June 1, 2025 sazenviro Post in Uncategorized Oily wastewater poses a major challenge in industrial effluent treatment due to the presence of free and emulsified oils, grease, and suspended solids. Industries like petroleum refining, food processing, textiles, and metal finishing often struggle to meet discharge norms without effective oil separation technology. Among the most efficient methods is Dissolved Air Flotation (DAF)—a system engineered to separate light, hydrophobic contaminants by floating them to the surface for removal. This article explains the role of DAF systems in oily wastewater treatment, and provides design insights, operational tips, and how to choose the right DAF unit manufacturer for your application. What Is a Dissolved Air Flotation (DAF) Unit?Contents1 What Is a Dissolved Air Flotation (DAF) Unit?2 Why Use DAF for Oily Wastewater Treatment?2.1 Role of DAF in Oily Wastewater Treatment3 Key Components of a DAF Unit3.1 What a DAF Unit Manufacturer Typically Supplies4 How a DAF System Works5 Design Criteria for Oily Wastewater DAF Systems5.1 Key Factors in DAF Unit Manufacturer Design Proposals6 Applications of DAF in Industry6.1 Common Uses of DAF for Oily Wastewater Treatment7 Types of DAF Units7.1 Configurations Offered by a DAF Unit Manufacturer8 Pre-Treatment Requirements9 Automation and Control Features10 Case Study: DAF Unit in a Dairy Processing Plant (Egypt)11 Common Challenges in DAF Operation and Their Solutions12 Best Practices for DAF Performance13 Selecting a DAF Unit Manufacturer13.1 How to Choose the Right DAF Unit Manufacturer14 Top Global DAF Unit Manufacturers15 Conclusion A DAF unit is a water treatment device that removes suspended solids, oils, and greases by injecting fine air bubbles into the wastewater. These microbubbles attach to particulate matter and oils, reducing their density and causing them to float. The resulting float layer is skimmed off, and the clarified water exits from the bottom or overflow channel. Why Use DAF for Oily Wastewater Treatment? Role of DAF in Oily Wastewater Treatment Separates free and emulsified oils effectively Removes up to 90–95% of suspended solids Helps meet COD and BOD discharge limits Reduces organic load before biological treatment Prevents membrane fouling in RO/ZLD systems DAF is often the preferred primary treatment technology for petrochemical, dairy, meat processing, and textile effluents. Key Components of a DAF Unit What a DAF Unit Manufacturer Typically Supplies Component Function Flotation Tank Main vessel where separation occurs Recycle Pump Pressurizes a portion of treated water for air saturation Air Dissolution Vessel Injects and dissolves air under pressure Pressure Relief Valve Releases air-water mixture into flotation tank Coagulant/Floc Dosing Unit Enhances bubble-particle attachment Skimmer System Rotating or chain scraper to remove floated sludge Sludge Hopper Collects thickened sludge or float layer Control Panel Automates pumps, valves, dosing, and float removal How a DAF System Works Wastewater enters the flocculation tank where coagulants and flocculants are added to destabilize suspended particles and emulsions. A portion of the treated water is recycled and saturated with air in the pressurized vessel. When released into the main tank, the air comes out of solution as fine bubbles (20–50 microns). Bubbles attach to oil droplets and solids, causing them to rise and form a float layer. A surface skimmer removes the float layer while clarified water exits from the bottom. Design Criteria for Oily Wastewater DAF Systems Key Factors in DAF Unit Manufacturer Design Proposals Parameter Typical Range/Target Hydraulic Loading Rate (HLR) 4 – 10 m³/m²/hr Air-to-Solids Ratio (A/S) 0.015 – 0.04 Recycle Ratio 10 – 50% of inlet flow Bubble Size 20 – 50 microns Sludge Concentration (float layer) 3 – 8% solids Residence Time 15 – 30 minutes Dissolved Air Pressure 4 – 6 bar (typically) Applications of DAF in Industry Common Uses of DAF for Oily Wastewater Treatment Industry Application Example Oil & Gas Produced water treatment, refinery effluent Food Processing Fat, oil, and grease (FOG) removal from waste streams Textile Separation of dyes, emulsions, and surfactants Automotive Pretreatment of paint booth wash water Dairy & Slaughterhouses Separation of proteins, oils, and solids Chemical Manufacturing Removal of organic emulsions and polymers Types of DAF Units Configurations Offered by a DAF Unit Manufacturer DAF Type Description Conventional DAF Horizontal flow system with float scraper Circular DAF Radial flow with rotating skimmer Compact DAF Skid Modular, containerized unit for portable use High-Rate DAF Smaller footprint with enhanced recycle pressure Vertical DAF Designed for very limited space (less common) Pre-Treatment Requirements To improve the effectiveness of the DAF unit in oily wastewater treatment, the following are often used: Coagulants: Alum, PAC, ferric chloride Flocculants: Cationic or anionic polymers pH Adjustment: For optimal floc formation (usually pH 6.5–7.5) Oil-Water Separators (API units): For bulk oil removal before DAF Automation and Control Features Modern DAF systems are available with advanced automation options: PLC/SCADA-based operation Level sensors for float and sludge layers Automated chemical dosing pumps Flow and pressure monitoring Remote monitoring capability via GSM or cloud Case Study: DAF Unit in a Dairy Processing Plant (Egypt) Flow: 150 m³/day Influent Oil & Grease: 800 mg/L DAF Type: Compact skid with horizontal scraper Result: O&G reduced to <30 mg/L TSS reduced by 92% COD reduction: 45% (from 1800 to 990 mg/L) Improved downstream MBR membrane lifespan by 2× Common Challenges in DAF Operation and Their Solutions Challenge Cause Solution Poor float formation Inadequate coagulant/floc dosing Optimize chemical program and mixing system Sludge carryover High surface loading rate Reduce flow or increase tank surface area Excessive sludge blanket buildup Skimmer not operating properly Adjust skimmer speed or scraper interval Oil emulsions not separating Incorrect pH or insufficient air pressure Modify pre-treatment dosing and recycle ratio Best Practices for DAF Performance Regular calibration of chemical dosing pumps Clean recycle pumps and air dissolution vessel weekly Backflush nozzles to avoid clogging Use coagulant aids (e.g. lime) for tight emulsions Monitor A/S ratio and recycle pump efficiency Compact Effluent Treatment Plants Selecting a DAF Unit Manufacturer How to Choose the Right DAF Unit Manufacturer Application Experience– Does the manufacturer have references in your industry? Design Flexibility– Can they size and configure the DAF unit based on variable flow and contaminant loads? Automation Capability– Are SCADA/remote control options offered? Local Support– Critical for spares and emergency servicing Export Readiness– For international projects, packaging, manuals, and compliance matter Top Global DAF Unit Manufacturers HydroFloTech (USA)– Offers oil & gas-focused DAF systems KWI International (Austria)– Specialized in large-scale municipal and food processing plants FRC Systems (USA)– DAF for high-COD and oily water recovery SAZ ENVIRO (India, Export-Ready)– Compact and conventional DAF systems– Capacity: 1–1000 m³/hr– Pre-engineered skids with dosing systems– Installed in UAE, Ghana, Kenya, Oman, Bangladesh– FRP, SS 304/316, and containerized units available Conclusion The DAF system is one of the most effective and reliable technologies for treating oily and high-TSS industrial wastewater. It offers superior oil, grease, and solids removal with a relatively compact footprint and rapid startup time. By choosing a proven DAF unit manufacturer, you gain access to application-specific expertise, automated dosing integration, and optimized design—ensuring long-term compliance and low operating costs. For industries seeking consistent and efficient oily waste water treatment, Dissolved Air Flotation is the gold standard.