Reverse Osmosis Desalination Technology

High Pressure Membrane Technology

• Has taken over thermal desalination for drinking water production since 1984-1995 due to innovations in energy recovery systems and high-efficiency permeable membrane materials.

Reverse Osmosis (RO)

• A membrane-based demineralization technique used to separate dissolved solids, such as ions, from solution.
• Can effectively remove radium, natural organic substances, pesticides, cysts, bacteria, and viruses.
• Membranes act as perm-selective barriers, allowing certain species (like water) to permeate through while retaining other dissolved species (like ions).

Osmosis & Reverse Osmosis

• Osmosis: a natural phenomenon where water flows across a semi-permeable membrane from low-concentrated to high-concentrated solutions due to chemical potential.
• Reverse Osmosis: applying additional pressure to reverse the flow from high salt to low salt side, allowing water to flow in the opposite direction.

Advantages of RO

• Removes nearly all contaminant ions and most dissolved non-ions.
• Operates immediately, without a minimum break-in period.
• Bacteria and particles are also removed.
• Operational simplicity and automation allow for less operator attention and make RO suitable for small system applications.
• Compact construction of systems provides lower investment for buildings and space than conventional treatment.

Limitations of RO

• High energy consumption mainly due to membrane fouling, which reduces efficiency and limits its application.

Nanofiltration (NF)

• Membranes have a nominal pore size of approximately 0.001 μm.
• Require higher operation pressure than MF or UF.
• Can remove virtually all cysts, bacteria, viruses, and humic materials.
• Also removes hardness from water, sometimes called “softening membranes.”
• Hard water treated by NF requires pretreatment to avoid precipitation of hardness ions on the membrane.

Membrane-Based Desalination Technologies

• Membrane processes (RO, ED, MD, and FO) are increasingly used for removal of bacteria, microorganisms, particulates, and natural organic material from water.
• These processes can be grouped under the common head of membrane-based desalination techniques.

Other Desalination Techniques

• Electrodialysis (ED): uses an electric potential to pass saltwater through a series of stacked anionic and cationic membranes.
• Other techniques include microfiltration (MF), ultrafiltration (UF), and forward osmosis (FO).