RO Recovery & Scaling Potential Calculator
Estimate how reverse-osmosis recovery changes mineral saturation in dilute freshwater.
Experimental screening calculator. This self-contained screening model operates at 5–35 °C, pH 6–9.5 and ionic strength no greater than 0.01 mol/L in both feed and concentrate. Unsupported waters are rejected. It is not a seawater/brine calculator or a validated membrane-design model.
1. Feed-water analysis
Use dissolved concentrations from the same sample after pretreatment. Required fields are marked *. Use a decimal point; leave unknown optional measurements blank. Enter zero only when justified by the analysis. Do not enter laboratory “less-than” results as zero.
Cations
Anions and other measurements
Enter calcium as Ca, not total hardness. Enter alkalinity once as CaCO₃, not as bicarbonate. Sulfate is as SO₄, not sulfur; silica is as SiO₂, not silicon. Phosphate and other unlisted contributors are assumed negligible.
2. Operating conditions
Try the reference-water examples
Two published Sierra Nevada spring analyses from USGS PHREEQC Example 16. Each button loads the feed analysis at 25 °C and evaluates 70% recovery. You may then change temperature within 5–35 °C and recalculate. Missing trace-ion measurements remain unknown.
The synthetic example adds trace ions to the perennial composition to exercise barium-sulfate warnings. It is a constructed test, not a published reference water.
Enter a water analysis or load an example.
3. Screening results
Results are displayed to two decimal places; calculations retain full precision. Nonzero positive values below 0.01 are shown as <0.01. Ionic strength is displayed in mmol/L. Reference-example inputs are rounded for display and retain their original precision until edited.
| Ideal concentration factor | |
|---|---|
| Estimated concentrate pH | |
| Concentrate ionic strength | |
| Signed feed charge imbalance |
| Mineral phase | SI | Saturation ratio | Interpretation |
|---|
Recovery comparison
| Recovery | Concentration factor | Screening outcome |
|---|
Interpret the result
SI = log₁₀(ion-activity product ÷ equilibrium constant). A positive SI indicates supersaturation for the named phase; it does not predict deposition rate, deposit mass or a suitable antiscalant dose. A ratio of 10 means ten times the thermodynamic saturation ratio, not 10% scale. The display band from −0.10 to +0.10 SI is a review band, not a universal safety or analytical-uncertainty limit.
A supersaturation warning means that scale control needs assessment. Possible responses include a lower recovery, appropriate pretreatment or a supplier-validated antiscalant programme. The calculator does not select a product or dose. “Undersaturated” is not a guarantee of scale-free membrane operation or low corrosion.
Calculation method and boundaries
- Ideal concentration factor = 1 ÷ (1 − recovery as a fraction), with complete retention of ions and dissolved inorganic carbon.
- Concentrate pH is solved at the entered temperature from conserved inorganic carbon and alkalinity, without precipitation, dosing, gas exchange or CO₂ passage. Enter feed pH measured at that same temperature; changing temperature does not simulate heating or cooling a fixed-carbon feed.
- Activities use the Davies equation with a temperature-dependent activity coefficient and iterative carbonate/silicate acid–base speciation. Dissolved metal, sulfate and fluoride totals approximate free-ion concentrations; ion pairs and metal complexes are omitted.
- Mineral equilibrium constants follow WATEQ4F analytical temperature expressions over 5–35 °C. Nominal log K values at 25 °C: calcite −8.48; gypsum −4.58; anhydrite −4.36; barite −9.97; celestite −6.63; fluorite −10.60; amorphous silica −2.71. Water activity is approximated as one.
- Mass concentration approximates molal concentration for dilute water. Feed charge imbalance above 5%, unsupported pH, temperatures outside 5–35 °C, or feed/concentrate ionic strength above 0.01 mol/L stop the calculation.
- Unknown optional constituents are omitted from ionic-strength and alkalinity corrections; their mineral rows are not assessed. Other outputs remain conditional on those missing contributions being negligible.
- No membrane staging, salt passage, concentration polarisation, precipitation kinetics or inhibitor efficacy is modeled. The comparison is an ideal bulk-concentrate screen.
Reference checks
Checked against PHREEQC 3.8.6 with WATEQ4F: two USGS spring analyses plus a separate synthetic trace-ion case, at 5, 10, 15, 20, 25, 30 and 35 °C, each at 0% and 70% ideal water removal. All 42 comparisons met the preselected screening criteria of absolute SI difference ≤0.10 and pH difference ≤0.05. Observed maximum differences were less than 0.08 SI units and less than 0.01 pH units. The temperature variants and concentrates are modeled test cases, not measured reference waters at those conditions. These checks cover those cases, not all waters within the input range.
USGS reference spring analyses · PHREEQC methodology · DuPont barium sulfate scaling method