RO recovery, rejection and concentration factor
Calculate system recovery, salt rejection and concentration factor from feed, permeate and concentrate flows and TDS readings.
Results
| System recovery | 70% |
|---|---|
| Salt rejection | 97% |
| Concentration factor | 3.33× |
| Concentrate flow | 3 m³/h |
| Estimated concentrate TDS | 6 527 mg/L |
At 70% recovery the concentrate carries salts at roughly 3.3× feed concentration. Single-stage arrays typically run 50–60%; 2:1 two-stage arrays reach 70–75% where the water chemistry allows.
Formula used
R = Qp ÷ Qf × 100
SR = (1 − TDSp ÷ TDSf) × 100
CF = 1 ÷ (1 − R ÷ 100)
Qc = Qf − Qp
TDSc = (Qf × TDSf − Qp × TDSp) ÷ Qc
- R
- system recovery, %
- SR
- salt rejection, %
- CF
- concentration factor, assuming complete salt rejection
- Qf
- feed flow, m³/h
- Qp
- permeate flow, m³/h
- Qc
- concentrate (reject) flow, m³/h
- TDSf/p/c
- TDS of feed / permeate / concentrate, mg/L
Straight mass balance around the membrane array, assuming steady state and TDS as a conserved lumped parameter. CF = 1 ÷ (1 − R) is the limiting case where the membrane passes no salt at all; at a real 97–99% rejection it runs a couple of percent high, and the concentrate figure to use is the TDSc row below it, which uses the salt actually measured. Concentrate TDS is an estimate; individual sparingly-soluble salts concentrate at their own rates; check saturation indices against the full analysis.
The background
- How reverse osmosis works: pressure, rejection and recoveryRO pushes water backwards through nature's preferred direction. Three numbers (osmotic pressure, rejection and recovery) describe everything an RO system does.
- Permeate quality: what TDS to expect and why it driftsRO permeate is very good water, though never perfect, and its quality moves with temperature, recovery, pressure and time. What to expect, what is normal drift, and what is a fault.
- Fouling versus scaling: telling them apart, preventing bothFouling and scaling both degrade an RO plant, but they show up in different places, with different symptoms, and need opposite cures. Diagnosing which one you have is half the repair.
Equipment for this duty
Send the water analysis and duty point, and the branch confirms exact selections, pricing and lead times, usually within one working day.
Request a quoteResults are indicative engineering estimates based on standard formulas and typical assumptions. They are not a design service; confirm any design against a full water analysis and the relevant manufacturer’s data.