Reverse osmosis technology

Operating principle

Reverse osmosis uses pressure greater than the osmotic pressure to drive water through a semipermeable membrane. The membrane separates the feed into a purified water stream, called permeate, and a stream with a higher concentration of dissolved substances, called concentrate or retentate.

The process operates without a phase change. It is used for desalination of water with a high mineral content, purification of surface water and wastewater, and preparation of water for commercial and industrial applications.

Process configuration

A typical system includes feed pretreatment, a high-pressure pump and membrane modules. Further treatment stages can be added where higher purity or concentration is required. Combined processes may use ultrafiltration, ion exchange, evaporation or other separation methods.

BOX4WATER system components

• An antiscalant dosing system with a solution tank, electronic diaphragm dosing pump, delivery line and dosing nozzle.
• A protective cartridge filtration stage before the reverse osmosis section.
• Spiral-wound thin-film composite membrane elements.
• A vertical multistage centrifugal high-pressure pump.
• An electrical control cabinet with a microprocessor, digital display and operating instruments.

Design considerations

Performance depends on the feed salt concentration, osmotic pressure, pressure applied to the membrane, temperature, membrane permeability, selectivity and available membrane area.

Pretreatment and operating conditions are selected to control fouling and concentration polarisation and maintain membrane performance. The required permeate quality, recovery and concentrate handling are considered as part of the overall treatment process.