How it works
- against osmosis — Left alone, water moves from dilute to concentrated. RO reverses that by brute force: apply more than the osmotic pressure and water is pushed the other way, leaving the salt behind. Roughly 0.7 bar per 1000 mg/L is the price of entry before any water moves at all.
- along the vessel — Water leaves as permeate, so the feed concentrates as it travels. By 75 % recovery the concentrate is around four times the feed. Osmotic pressure rises with it, so the last element works hardest and produces least — the reason arrays are staged 2:1.
- flux and area — Flux is permeate per square metre per hour. Push it above roughly 20 LMH on brackish water and the concentration polarisation layer at the wall thickens, rejection falls and scaling starts. Low flux is a design choice, not a compromise.
- concentrate recycle — Returning part of the concentrate to the pump suction lifts system recovery when you cannot afford the reject. It also raises the feed concentration at the membrane, because the salt is still in the loop — so recovery on paper improves while the lead element walks toward scaling.
- what governs it — Feed pressure must beat osmotic pressure plus what the flux demands, and that sets the energy bill. Recovery sets the concentrate strength and therefore the scaling limit. Drag recovery up and watch concentrate TDS and feed pressure climb together — they always do.
Design parameters
The panel opposite runs the same correlations as the RO-600 design sheet, so the animation and the calculator cannot disagree. Drag any of them and the picture responds.
- Feed flow — m³/h
- Feed TDS — mg/L
- Recovery — %
- Salt rejection — %
- Design flux — LMH
- Temperature — °C
Open the full RO-600 design sheet for the governing equations, the accepted design envelopes and the worked calculation.