Reverse Osmosis Water Purification: Step-by-Step Breakdown

Reverse osmosis is a pressure-driven filtration process that removes dissolved salts, organic molecules, bacteria, and other impurities from water by forcing it through a semi-permeable membrane. It’s widely used in drinking water systems, agriculture, and industrial applications.

1. Feed Water Intake

• Source: Typically comes from municipal supply, boreholes, rivers, or seawater.

• Contents: Contains dissolved salts (like sodium, chloride), minerals, bacteria, viruses, and organic compounds.

• Pretreatment: Often passes through sediment and carbon filters to remove large particles and chlorine (which can damage the membrane).

2. High-Pressure Pump

• Purpose: Applies pressure to the feed water—typically 4–15 bar for freshwater, up to 70 bar for seawater.

• Why Pressure Matters: It must exceed the natural osmotic pressure to reverse the flow of water across the membrane.

3. Semi-Permeable Membrane

• Structure: Made of thin-film composite material with microscopic pores (~0.0001 microns).

• Function: Allows water molecules to pass through while blocking:

  • Dissolved salts

  • Heavy metals

  • Microorganisms

  • Organic pollutants

4. Separation Process

• Inside the Pressure Vessel:

  • Water flows tangentially across the membrane surface.

  • Clean water (permeate) diffuses through the membrane.

  • Concentrated waste (brine or concentrate) flows out separately.

• Efficiency: RO systems typically recover 30–80% of feed water depending on design and application.

5. Permeate Collection

• Output: Purified water with up to 99% of dissolved salts removed.

• Post-Treatment (Optional):

  • pH adjustment

  • UV sterilization

  • Mineral rebalancing (for taste or health)

6. Concentrate Disposal

• Waste Stream: Contains rejected contaminants.

• Handling: Can be discharged, reused (e.g., for irrigation), or further treated depending on environmental regulations.

Key Benefits of Reverse Osmosis

• Removes up to 99% of contaminants.

• No chemicals required for separation.

• Compact and scalable for home, farm, or industrial use.