Pressure Against Nature
Osmosis naturally drives water from dilute to concentrated solutions through a semi-permeable membrane. Reverse osmosis inverts this process by applying external pressure exceeding the osmotic pressure, forcing freshwater out of seawater. For typical ocean salinity of 35,000 ppm, the osmotic pressure is roughly 27 bar — so RO plants operate at 55–70 bar to maintain adequate flux through the membrane.
Membrane Performance
Modern thin-film composite (TFC) membranes achieve salt rejection above 99.5% while allowing permeate fluxes of 15–25 L/m²/h. The key parameter is membrane permeability (A-value), which determines how much water passes per unit pressure. Higher permeability means lower energy consumption, but membrane designers must balance permeability against selectivity — the permeability-selectivity trade-off is a fundamental constraint in membrane science.
Energy and Recovery
The specific energy consumption of RO depends critically on feed pressure and recovery ratio. Higher recovery extracts more freshwater per unit of feed but concentrates the brine, raising osmotic pressure along the membrane length. Energy recovery devices (pressure exchangers) capture up to 97% of the hydraulic energy in the reject brine, making modern RO the most energy-efficient desalination technology at 2–3 kWh/m³ for seawater.
Scale and Impact
Reverse osmosis dominates global desalination, accounting for 69% of installed capacity. The largest RO plant (Sorek B, Israel) produces 627,000 m³/day at costs below $0.50/m³. This simulation lets you explore how operating parameters affect performance — understanding why the industry converges on specific pressure and recovery windows for seawater versus brackish water applications.