Dissolved Air Flotation (DAF) Unit

Dissolved Air Flotation (DAF) units are widely utilised in industrial wastewater treatment processes to remove suspended solids, oils, and other contaminants. This document provides a comprehensive technical specification for DAF units,outlining their operating principle and key industrial applications.

Operating Principle of DAF Unit

The core operating principle of a DAF unit is based on the separation of suspended particles from water using microbubbles of air. The process involves saturating water with air at high pressure and then releasing it at atmospheric pressure within the flotation tank. This sudden release of pressure causes the dissolved air to come out of solution as fine bubbles. These microbubbles attach to the suspended solids, fats, oils, and other contaminants, reducing their effective density and causing them to float to the surface of the water. The floated material forms a sludge layer, which is then mechanically skimmed off for further processing or disposal. The clarified water exits from the bottom of the tank for reuse or discharge.

Key Components

  • Flotation Tank: The main chamber where separation occurs.
  • Air Saturation System: Utilises pressurised air to saturate water.
  • Recycle Pump: Recirculates a portion of treated water for air saturation.
  • Effluent Weir: Controls the outflow of clarified water.
  • Sludge Skimmer: Mechanically removes floated sludge.

Process Steps

  1. Wastewater enters the DAF unit.
  2. A portion of treated water is pressurised and saturated with air.
  3. Air-saturated water is released into the flotation tank at atmospheric pressure.
  4. Microbubbles form and attach to contaminants. 5. Contaminant-bubble aggregates float to the surface. 6. Sludge is skimmed off; clarified water is discharged.

Technical Specification

PARAMETERSPECIFICATION
Flow Rate5 m³/hr to 500 m³/hr (customisable)
Operating Pressure4 to 6 bars (in air saturation system)
Bubble Size10 to 100 microns
Tank Material Stainless Steel (SS304/SS316) or FRP
Retention Time5 to 30 minutes
Sludge RemovalMechanical skimmer (rotating or chain type)
Effluent QualitySS < 20 mg/L; Oil & Grease < 10 mg/L (depends on influent quality)

Industrial Applications of DAF Units

DAF units are widely deployed across various industries for effective solid-liquid separation and removal of oils and greases. Some key applications include:

  • Food and Beverage Industry: Treatment of process wastewater containing high levels of organic matter,suspended solids, and fats.
  • Oil and Gas Sector: Removal of oil, grease, and suspended solids from refinery effluent streams.
  • Pulp and Paper Mills: Clarification of white water and reduction of chemical oxygen demand (COD).
  • Chemical Manufacturing: Pre-treatment for removal of emulsified oils and solids before biological treatment.
  • Textile Industry: Treatment of dyeing and finishing wastewater to remove colour and solids.
  • Pharmaceuticals: Removal of active pharmaceutical ingredients and suspended solids from effluents.
  • Dairy Processing: Separation of fats, proteins, and other solids from wastewater streams.
  • Municipal Wastewater: Tertiary treatment for polishing effluent before discharge or reuse.

Conclusion

DAF units offer a reliable and efficient method for separating suspended solids, oils, and other contaminants from industrial wastewater. Their versatility and customisable design make them suitable for a wide range of industrial applications, contributing significantly to environmental compliance and resource recovery.