RO Recovery & Concentrate
Balance feed, permeate and concentrate flows and dissolved-solids mass.
Calculator inputs
Results
Equations and method
Permeate flow = feed × recovery. Concentrate flow = feed − permeate. Permeate concentration = feed concentration × (1 − rejection). Concentrate concentration = (feed mass − permeate mass) ÷ concentrate flow.
Worked example
At 100 gpm, 75% recovery, 1,000 mg/L feed TDS and 98% rejection: permeate = 75 gpm at 20 mg/L; concentrate = 25 gpm at 3,940 mg/L.
Scope and assumptions
Steady-state balance with negligible water-density differences and no precipitation, storage or other solute losses. Rejection is an input measured or assumed relative to feed concentration. This does not predict attainable recovery, scaling, pressure or membrane performance.
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Equation values and input guide
Enter feed flow and TDS, water recovery, observed rejection and active membrane area. Review both water and dissolved-solids balances. The entered recovery and rejection must be supported by actual operating or design information.
- Qf, Qp, Qc
- Feed, permeate and concentrate volume flows in a common unit. Qp = recovery × Qf and Qc = Qf − Qp.
- Cf, Cp, Cc
- Feed, permeate and concentrate dissolved-solids concentrations in mg/L. Use the same solute/TDS basis for all three.
- Recovery, rejection
- Water fraction recovered as permeate and fraction of feed concentration rejected. Enter percent; the equations use fractions. Cp = Cf(1 − rejection).
- Concentrate concentration
- Cc = (QfCf − QpCp)/Qc from solute conservation. High recovery leaves less concentrate water and raises its concentration.
- Active membrane area, flux
- Effective membrane area and permeate volume flow divided by that area. Flux is not calculated using feed flow.
Use the unit selectors beside the inputs. Units shown in the equations must be consistent when checking the math by hand.