RO Membrane Performance Calculator
A professional reverse-osmosis mass-balance and salt-passage verification tool supporting single- and multi-stage (up to 3-stage) concentrate-staged arrays with 4-, 8-, and 16-inch element sizing. Model net driving pressure, permeate flow, flux, and rejection across brackish, seawater, and municipal feed types.
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Our engineering team is actively designing and building this calculator's engine.
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Contact UsStandard Compliance
Need a custom review?
For multi-stage arrays, non-standard feed chemistry, or antiscalant/scaling verification, our engineers can provide a detailed process audit.
Request ConsultationExport Capabilities
- Professional PDF engineering reports
- Full mass-balance and salt-passage analysis
- Metric / Imperial unit conversion
- Brackish, seawater, and municipal feed presets
RO Membrane Performance Calculator
Reverse osmosis mass-balance, temperature correction, and salt-passage performance for single- or two-pass, up-to-3-stage concentrate-staged array configurations, with membrane-aging projection and product-water blending.
2- and 3-stage arrays feed each stage from the prior stage's concentrate, raising overall system recovery beyond what a single stage can reach.
Re-pressurizes Stage 1's concentrate before it enters Stage 2, independent of the main feed pump — useful when this stage would otherwise run short on net driving pressure, especially at high recovery or aged-membrane conditions.
Re-pressurizes Stage 2's concentrate before it enters Stage 3, independent of the main feed pump.
Defaults follow the selected feed water type; edit for a specific project. The "Aged" condition (toggle top-right) projects permeate TDS and required feed pressure at end of the stated membrane age — the design should stay within spec at BOTH Day-1 and Aged conditions.
Pass 2's feed is Pass 1's blended permeate, re-pressurized by an interstage pump (modeled as Pass 2's own feed pressure). Common for high-purity applications (boiler feed, semiconductor, pharma) and RO+EDI trains.
Pass 2 feed is Pass 1's permeate (very low TDS), so this selects the 2nd-pass membrane's own bench baseline and aging defaults, not a feed-water fouling classification.
Pass 2's final concentrate is already near permeate quality (it started from Pass 1 permeate), so recycling it into the raw feed instead of wasting it is standard practice and materially improves overall system recovery.
Optional raw/pretreated water blended directly into the final product stream to hit a target finished TDS without over-designing rejection. Leave flow at 0 to disable.
| Stage | Elements | Recovery | NDP | Flux | Rejection | Perm. Flow | Conc. Flow | Conc. TDS |
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| Stage | Elements | Recovery | NDP | Flux | Rejection | Perm. Flow | Conc. Flow | Conc. TDS |
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Inputs changed — click Calculate to refresh results above.
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Engineering Methodology
Mass-balance and flux calculations follow the standard recovery-based form (Qp = Qf·Y), with net driving pressure derived from feed pressure less concentrate-side losses and feed osmotic pressure.
Salt passage is temperature- and flux-normalized against the element's bench test-condition baseline, with a concentration-polarization factor applied to estimate real membrane-wall salt passage.
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