What Is the Recovery Ratio in RO Systems?

The recovery ratio is the value that indicates how much of the water entering a reverse osmosis (RO) system is produced as pure water (permeate).

In other words:

The recovery ratio shows how much of the feed water is converted into treated water.

In RO systems, the feed water is split into two streams:

1️⃣ Permeate (treated water)
2️⃣ Reject / Concentrate (waste water)

The recovery ratio expresses the relationship between these two streams.

Why Is the Recovery Ratio Important?

The recovery ratio is one of the most critical parameters in RO system design.

Choosing the wrong recovery ratio can lead to the following problems:

• membrane fouling
• scaling
• shortened membrane lifespan
• low production capacity

For this reason, the recovery ratio must be correctly determined when designing industrial RO systems.

Recovery Ratio Calculation Formula

The recovery ratio is calculated with the following formula:

Recovery % = (Permeate Flow / Feed Flow) × 100

Where:

Feed = water entering the system
Permeate = treated water

Sample Recovery Calculation

In an RO system:

Feed flow = 10 m³/h
Permeate flow = 7 m³/h

According to the formula:

Recovery = (7/10) × 100

Result:

Recovery = 70%

In this case, the system's recovery ratio is 70%.

Typical Recovery Values in Industrial RO Systems

The recovery ratio varies according to water quality.

It is generally designed within the following ranges:

The higher the recovery ratio, the greater the water yield, but the greater the load on the membrane as well.

Factors Affecting the Recovery Ratio

There are many factors that determine the recovery ratio.

1️⃣ Feed Water Quality

The quality of the feed water directly affects the recovery ratio.

The following parameters are especially important:

• TDS (Total Dissolved Solids)
• hardness
• silica
• alkalinity
• SDI

In waters with a high TDS value, the recovery ratio should be kept lower.

2️⃣ Membrane Type

The membrane model used in RO systems also affects the recovery value.

The most commonly used membrane brands on the market are:

• Dow Filmtec
• Hydranautics
• Toray
• LG Chem
• Vontron

Each membrane has different operating limits.

3️⃣ Use of Antiscalants

To prevent scaling, antiscalant chemicals are used in RO systems.

Using antiscalants can increase the recovery ratio.

Some chemical brands used in industrial systems:

• Genesys
• Avista
• Nalco
• BWA Water Additives

Proper dosing directly affects recovery performance.

4️⃣ RO System Design

RO system design has a major impact on recovery.

For example:

• single-stage RO
• two-stage RO
• three-stage RO

systems have different recovery ratios.

Multi-stage RO systems can achieve higher recovery.

Multi-Stage Recovery in RO Systems

In industrial systems, multi-stage design is used to increase recovery.

Example:

Stage 1

Feed = 10 m³/h
Permeate = 5 m³/h

Stage 2

The reject water is fed back into the system.

Permeate = 2 m³/h

Total

Permeate = 7 m³/h

Recovery = 70%

This method saves water.

What Happens If the Recovery Ratio Is Too High?

If the recovery ratio is increased more than necessary, the following problems can occur:

• membrane scaling
• membrane fouling
• decreased permeate quality
• shortened membrane lifespan

For this reason, the optimum recovery ratio must be determined in system design.

What Happens If the Recovery Ratio Is Too Low?

If the recovery ratio is chosen too low:

• water yield decreases
• the amount of waste water increases
• operating costs rise

For this reason, the right balance must be established.

Design Example for Industrial RO Systems

Let's consider a sample RO system:

Feed = 20 m³/h

Recovery = 65%

Permeate = 13 m³/h

Reject = 7 m³/h

These values are considered ideal for many industrial systems.

Software Used in RO System Design

The following software is used in professional RO system design:

• ROSA (Dow)
• IMSDesign (Hydranautics)
• Toray DS
• LG Chem design software

These programs optimize membrane design and the recovery ratio.

Conclusion

In industrial RO systems, the recovery ratio is one of the most important parameters determining system efficiency.

Thanks to the right recovery ratio:

• water yield increases
• membrane lifespan extends
• operating costs decrease.

For this reason, when designing an RO system, the recovery ratio must always be determined based on water analysis and engineering calculations.