Reverse Osmosis Engineering Tools

Which RO calculation do you need?

Start from the question, not the tool. Each family below states what it solves, when it applies, and what to reach for afterwards.

1. What fraction of the feed becomes product — and how much is left as concentrate?

   At the start of any RO balance, whenever a product flow has to be turned into a feed flow or a recovery has to be checked against a real feed.

   • RO Recovery Calculator RO recovery and permeate flow with full water and salt balance closure, concentrate concentration and salt loads.
   • RO Concentrate Flow Calculator Brine/reject flow with water and salt balance closure, concentrate TDS, concentration factor and salt loads.
   • RO Mass Balance Calculator Simplified TDS-based dissolved-solids balance for RO feed, permeate, and concentrate flow and quality checks.

   Then: Confirm the salt side next: salt rejection and passage decide the product quality and the concentrate TDS that recovery creates.

2. How good is the product, and what does the concentrate end up carrying?

   When a product specification has to be demonstrated, or a concentrate quality needs to be justified against a scaling limit.

   • RO Salt Rejection Calculator Calculate membrane salt rejection percentage from feed and permeate TDS concentrations.
   • RO Salt Passage Calculator Determine salt passage percentage through RO membranes and verify complementary rejection balance.
   • RO Permeate TDS Calculator Project expected permeate total dissolved solids based on feed water salinity and rejection specs.

   Then: Check the pressure and energy those flows imply, then confirm the membrane area supports the duty.

3. What pressure does the membrane actually need, and what does it cost in power?

   When sizing the high-pressure pump, checking an operating pressure, or pricing the energy of a design.

   • RO Osmotic Pressure Calculator Estimate RO feed osmotic pressure using a simplified van’t Hoff model from TDS, temperature, and solute properties.
   • RO Feed Pressure & Specific Energy Calculator Estimate required RO feed pressure (permeate osmotic gap + net driving pressure) and specific energy consumption with optional energy recovery.
   • RO Energy & Specific Power Calculator Determine specific energy consumption (kWh/m³) based on operating pressure and pump efficiency, with optional energy recovery device savings.
   • RO Operating Cost (OPEX) & SEC Calculator Estimate RO operating expenditure: pumping energy (specific energy consumption), chemical cleaning, antiscalant, and membrane replacement.

   Then: Confirm the membrane area and the scaling envelope, then move the whole set into the Plant Designer so it stays consistent.

4. How much membrane is needed, and is the recovery defensible?

   When converting a duty into elements and vessels, or when establishing the highest recovery the concentrate will tolerate.

   • RO Membrane & Vessel Element Count Calculator Calculate number of RO membrane elements and pressure vessels from permeate flow, design flux, and element area.
   • RO Scaling Risk & Pretreatment Analysis Screen CaCO3 scaling risk in RO feed and concentrate using the Langelier Saturation Index (ASTM D3739) and the Stiff & Davis Stability Index (S&DSI) for high-TDS and seawater feeds.

   Then: Size the pretreatment that protects the membrane, then carry the balance forward in the Designer.

5. Why is the running plant not performing as designed?

   For an existing installation: recovery below expectation, product quality drifting, or a feed-pressure change that needs explaining.

   • RO Performance & Troubleshooting Analyzer Compare a current measured RO run against its commissioning baseline: permeate flow normalized to 25 °C and baseline net driving pressure (ASTM D4516-style), salt passage, pressure drop, flux and specific flux — with directional, verify-in-the-field diagnostics.

   Then: Treat the output as diagnosis input for an engineer, not as a substitute for a site investigation.