Reverse Osmosis Permeate Flux & Recovery Calculator

Determine membrane permeate flux ($LMH$ / $GFD$), recovery percentage ($Y$), salt rejection, and Net Driving Pressure ($NDP$).

RO System Flow & Pressures

Feed Flow Rate Q_f (m³/hr):

Permeate Flow Rate Q_p (m³/hr):

Feed Total Dissolved Solids TDS_f (mg/L):

Permeate TDS_p (mg/L):

Feed Operating Pressure P_f (bar):

Concentrate Exit Pressure P_c (bar):

Total Active Membrane Area A_m (m²): Standard 8-inch element: ~40 m² (440 ft²)

Feed Water Temperature (°C):

Flux, Rejection & Driving Pressure

System Recovery Rate (Y):

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Permeate Water Flux:

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Salt Rejection Percentage:

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Concentrate TDS (TDS_c):

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Average Osmotic Pressure (Δπ):

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Net Driving Pressure (NDP):

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Reverse Osmosis Solution-Diffusion Principles

Semi-permeable thin-film composite (TFC) polyamide membranes separate pure water from dissolved ionic species via solution-diffusion. Water transport is driven solely by the Net Driving Pressure (NDP), which is the mechanical hydraulic pressure applied minus the natural osmotic back-pressure: $$J_w = A \cdot (\Delta P - \Delta \pi) = A \cdot \text{NDP}$$

Recovery Rate & Scaling Thresholds

As recovery ($Y = Q_p / Q_f$) increases, mineral ions are concentrated into a progressively smaller volume of brine. In brackish water plants operating at $75\%$ recovery, concentrate TDS is approximately $4\times$ higher than feed water TDS. Exceeding solubility limits for calcium sulfate ($\text{CaSO}_4$) or silica ($>150\text{ mg/L}$) will cause irreversible scaling without antiscalant dosing.

Reverse Osmosis Permeate Flux & Recovery Calculator

RO System Flow & Pressures

Flux, Rejection & Driving Pressure

Reverse Osmosis Solution-Diffusion Principles

Recovery Rate & Scaling Thresholds

Frequently Asked Questions