How to Read an RO Projection Report: Recovery, Flux and Rejection in Plain Language

When you request a quotation for an industrial RO plant, a serious supplier will usually attach a membrane projection report. It is generated by design software from the membrane manufacturer and runs to several pages of numbers. Many buyers skim it and flip straight to the price. That is a mistake, because the projection quietly tells you whether the plant has been designed conservatively or squeezed to win the order.

Start with the Feed Water Analysis

Every projection begins with an input water analysis. Check that it actually matches your source. A report built on an old or borrowed analysis is worthless. Look for calcium, magnesium, sodium, bicarbonate, sulphate, chloride, silica, pH, temperature and total dissolved solids. If silica, barium or strontium are missing, ask why, because these ions often limit how hard the plant can be pushed.

Temperature deserves special attention. Membranes produce less water in cold conditions, so the design should be checked at the lowest expected feed temperature, not just a comfortable average.

Recovery: How Much Water You Keep

Recovery is the percentage of feed water that becomes permeate. A plant fed with 100 m3/hr that produces 75 m3/hr of permeate runs at 75 percent recovery, and the remaining 25 m3/hr is reject.

Higher recovery sounds attractive because you waste less water. The catch is that the salts in the reject become more concentrated, raising the risk of scaling. A good projection will show saturation levels of calcium carbonate, calcium sulphate, barium sulphate and silica in the concentrate. If those numbers sit far above saturation, the design is depending heavily on antiscalant, and you should understand that risk before accepting it.

Flux: How Hard Each Membrane Works

Flux is the permeate flow divided by the total membrane area, usually expressed in litres per square metre per hour (LMH). It is one of the most important indicators of design quality.

Why Lower Flux Is Usually Safer

A plant running at high flux pulls water through the membrane faster, dragging foulants onto the surface. It may need fewer membranes and look cheaper, but it will foul quicker and need more frequent cleaning. Membrane manufacturers publish recommended flux ranges based on water source. As a broad guide, well-pretreated surface water and wastewater reuse applications call for noticeably lower flux than clean well water.

Compare the average flux in competing quotations. A design with fewer membranes and a much higher flux is not a bargain.

Salt Rejection and Permeate Quality

The projection shows expected permeate quality ion by ion. Check the projected TDS and the specific ions that matter to you, such as chloride for boiler feed or sodium for beverage applications. Remember that projections assume new membranes. Rejection typically declines a little over the years, so leave some margin if your final quality limit is tight.

Feed Pressure and Energy

The required feed pressure tells you about pump sizing and running cost. Higher pressure means more electricity. A projection should also show the expected pressure after a few years of membrane ageing, often called the end-of-life or fouled condition. If only new-membrane pressure is shown, ask for the aged scenario too.

Array and Staging

The array describes how pressure vessels are arranged, for example 4:2 means four vessels in the first stage feeding two in the second. Staging keeps cross-flow velocity high enough to sweep foulants away as water is removed. Check that concentrate flow per vessel stays within the manufacturer’s minimum, and that the feed flow per vessel does not exceed the maximum. Warnings printed in the report should never be ignored.

Red Flags to Watch For

• Design warnings left unresolved in the printout
• Flux well above the guideline for your water type
• Concentrate saturation levels that rely entirely on antiscalant
• No projection at minimum temperature or aged membrane condition
• A water analysis that does not match your actual source

The Bottom Line

The projection report is the engineering heart of an RO quotation. Spending half an hour understanding it can save years of high cleaning costs and premature membrane replacement. If anything in the report is unclear, ask your supplier to walk you through it. A confident, honest supplier will welcome the conversation.

Need help with your water or wastewater project? Aguapuro Equipments designs, supplies and services water treatment, effluent treatment and bottling solutions. Send us an enquiry or contact our team to discuss your requirements.