DAP Water Filtration Process

The DAP process (Dissolved Air Flotation, Adsorption, and Precipitation) is an advanced method used in water treatment plants, especially when conventional sedimentation is less effective—such as with low-density particles, algae, or oily substances. Here’s a breakdown of the water filtration process using the DAP method:

1. Coagulation & Flocculation

  • Coagulants added: Chemicals like alum or ferric chloride are dosed into the raw water.

  • Mixing: Rapid mixing disperses the coagulant; slow mixing promotes the formation of floc (clusters of particles and contaminants).

2. Adsorption (A in DAP)

  • Adsorbents introduced: Materials like powdered activated carbon (PAC) are sometimes added to adsorb organic compounds, taste, odor, or micropollutants.

  • Interaction: Contaminants adhere to the surface of the adsorbent, enhancing the overall removal efficiency.

3. Precipitation (P in DAP)

  • Chemical reaction: Some dissolved substances (like heavy metals or phosphates) form insoluble precipitates when pH or other conditions are adjusted.

  • Formation of solids: These precipitates combine with floc for easier removal in the next step.

4. Dissolved Air Flotation (DAF – the D in DAP)

  • Air injection: Water is saturated with air under pressure, then released into a flotation tank at atmospheric pressure.

  • Bubble formation: Tiny air bubbles form and attach to floc and other particles.

  • Floating sludge: The bubbles lift the floc to the surface, where it forms a floating sludge layer.

  • Skimming: This layer is mechanically skimmed off, removing contaminants.

5. Filtration

  • Filtration media: The clarified water from DAF is passed through sand, anthracite, or other media filters.

  • Purpose: This step removes any remaining particles or residual floc.

6. Disinfection and Final Treatment

  • Disinfection: Chlorine, UV, or ozone is used to kill pathogens.

  • Polishing steps: pH adjustment, fluoridation, or further adsorptive treatments (like GAC) may be applied based on the desired water quality.

7. Distribution

  • The fully treated and safe water is stored and then pumped through the municipal distribution system.