Understanding Reverse Osmosis Systems: Key Terms Explained

There are many important terms related to reverse osmosis (RO) systems. Knowing and understanding these terms can help you find the right system for your business needs. Here are a few key terms to know:

  1. Reverse Osmosis Recovery Rate

The recovery rate of an RO system refers to the amount of water it successfully converts into permeate or product water. Typically, RO systems achieve a recovery rate of 75%, but it can range from 50%-90% depending on the design of the RO system and the feed water quality. As an example, for every 100 gallons of feed water that enters the RO system, 75 gallons become permeate while 25 gallons are concentrate. Adjusting the recovery rate affects water wastage and permeate quality. Higher recovery rates mean less water wasted but lower quality permeate, while lower recovery rates result in better quality permeate but more wasted water as concentrate.

Optimizing the Recovery Rate

Optimizing the recovery rate in reverse osmosis systems is crucial. A higher recovery rate reduces the amount of water discharged as concentrate but compromises the quality of permeate water. Exceeding the system’s designed recovery rate leads to rapid scaling and fouling of membranes because insufficient water is available to cleanse rejected contaminants.

Conversely, reducing the recovery rate improves permeate quality and diminishes scaling and fouling risks, yet significantly increases water wastage through concentrate discharge.

Adjusting the recovery rate with the concentrate valve

The concentrate valve can be throttled to adjust the recovery rate and to find the optimal balance. As you close the concentrate valve, you will increase the recovery rate. When the concentrate valve is opened, it will decrease the recovery rate. However, it is very important to know that the concentrate valve should never be fully closed.

How to calculate the RO recovery rate

The formula for determining the recovery rate is:

Recovery Rate Percentage = permeate flow / by the feed flow.

  1. Permeate Flow Rate

RO systems are rated by their permeate flow rate. It is measured in gallons per minute (GPM) or gallons per day (GPD). This rate specifically indicates how much permeate water the RO system produces.

  1. Concentration FactorA table that shows the recovery rate of 75%,80%, 83%, 87.5% corresponding to a concentration factor of 4,5,6,8, respectively.

The concentration factor is directly tied to the recovery rate and reflects how much contaminants are concentrated in the concentrate stream. For instance, a 75% recovery rate results in a concentration factor of four, meaning contaminants in the concentrate are four times more concentrated than in the feed water.

  1. Salt Rejection

Salt rejection measures the effectiveness of an RO system in removing contaminants from feed water. Typically, RO systems achieve 97% to 99% salt rejection. This percentage indicates the purity of the permeate water—higher rejection rates mean lower TDS (total dissolved solids) in the permeate.

Impact of Small Changes

Small adjustments in recovery rate and salt rejection percentage can significantly impact both the quality and quantity of permeate water. For example, a slight decrease in salt rejection from 99% to 98% can double the TDS in the permeate. This affects its overall quality and the operational longevity of downstream equipment like ion exchange tanks.

The Importance of Finding the Right RO System

Understanding these terms—recovery rate, permeate flow rate, concentration factor, and salt rejection—provides clarity on how to evaluate the efficiency and output quality of reverse osmosis systems. Whether you’re concerned about water wastage, permeate quality, or system longevity, these metrics offer crucial insights into optimizing RO performance to meet your specific needs.

Knowing these terms can help you make informed decisions about selecting, operating, and maintaining reverse osmosis systems.