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Reverse Osmosis and Ion Exchange: What's the Difference?

Reverse Osmosis and Ion Exchange: What's the Difference?

Reverse osmosis (RO) or ion exchange: which one is better for you? If this is what you are wondering, then you have come to the right place. We will discuss what these filters are and which one will work better based on your requirements and needs.

What is Ion Exchange?

It is a method that helps with domestic water softening and demineralization of wastewater. These water filters remove ions from the water by exchanging them with another ion. This helps bond the weak ions with the strong bonding ions. Experts call this the reactivity-selectivity principle. Filters use this principle to remove contaminants and unwanted particles from water.  

You also need to know that filters use the ion exchange technique either in continuous mode or batch mode. The ion exchange method greatly helps with wastewater purification to remove phosphorous, nitrogen, and heavy metals.

In addition, this filtration method helps get rid of specific impurities as well as harmful metals such as nickel, lead, chromium, copper, and cadmium from impure water.

What is Reverse Osmosis?

Reverse Osmosis (RO) is a system that makes desalination (or removal of salt from seawater) possible. Beyond that, reverse osmosis is used for recycling, wastewater treatment and can even produce energy. The process uses a semi-permeable membrane (also known as synthetic lining) in order to filter out large particles and unwanted molecules such as sediments and contaminants, such as chlorine, salt, and dirt particles from drinking water.

You also need to know that the movement of water occurs against a concentration gradient. Moreover, the membranes used in the RO are known as reverse osmosis (RO) membranes. Experts use several materials to produce commercial RO membranes.

They include cellulose acetate (CA), thin-film composites (TFC), and cellulose triacetate (CTS). The efficiency and speed of the RO mainly depend on the material of the membrane.

Besides that, the reverse osmosis setup uses a hollow fiber. And a membrane material is wounded around this fiber. To increase the surface area and filter water, experts bind these fibers together. When the water starts to flow with high pressure, small molecules also pass through the semi-permeable membrane with the water. The particles get trapped in the membrane, and filtered water passes it and reaches downstream processing. 

Differences between Ion Exchange and Reverse Osmosis System

Both ion exchange and reverse osmosis systems are popular and provide you with clean water. But both are very different from each other.

Hardness Removal

If magnesium and calcium are present in the process stream, they can lead to scaling on the downstream equipment and RO membranes. To boost the RO efficiency and life span, most people install ion exchange systems before the RO filters so that the water stream can pass through the ion exchanging system before the RO.

Although RO may not always be an affordable option for you, it will help reduce the total dissolved solids (TDS) in water. As RO constantly offers you pure water, it makes it suitable for almost every type of application that requires low conductivity.  This is the primary reason why people purchase these filters over ion exchange filters.

Bacteria Reduction

During water filtration, disinfection is the deactivation and removal of the pathogens such as viruses, bacteria, and protozoa and any pathogenic compound these elements produce, such as algal toxins. It is important to note that ion-exchange filters are not the best option to remove bacteria from water.

On top of that, there are some chemical disinfectants that have the ability to degrade resins present in this filter. This is why you need to keep up with proper maintenance so that you can remove these type of materials from the filter’s columns to save yourself from high replacement costs.

Since pathogens are comparatively bigger than the water molecules, a reverse osmosis system can effectively help you remove bacteria from water. Due to this property, people use it for applications that need extremely pure water. However, RO systems can cost you more than any other water filtration system on the market.

Particles and Suspended Solids

As RO separates impurities and contaminants based on their size, this means that any molecule and particles that are larger in size than the RO membrane’s pores can accumulate in the retentate of the semi-membrane. Due to this, RO has the ability to get rid of suspended solids and particulates.

However, RO filters are not ideal for carrying out this procedure. This is because these particles can reduce the life of the filter and lead to high operational costs.

On the other hand, ion exchange doesn’t have the ability to remove suspended solids and particles, such materials, which can lead to inferior performance and clogging in the filter’s resin beds. Typically, if the streams contain suspended solids, experts recommend using upstream filtration.


It’s true that an RO system is relatively more efficient and beneficial; however, it offers you a slower rate of water filtration than other filtration systems. Furthermore, it also produces a high quantity of wastewater than ion exchange filters.

Ion exchange produces around 2% to 4% wastewater, while RO can produce 10% to 50% (on average) of the volume of treated water. This is why, if you live in a location that offers limited water to your house or has high wastewater disposal costs, ion exchange is the best option for you. It doesn’t require a high quantity of water to offer you safe and clean water.

You can read about our other popular reviews on CulliganKineticoRayne Water, and waterboss.

Bottom Line

If you are on a tight budget and usually experience water shortages in your area, it’s better to go with ion exchange filters.

However, if your water supply is highly contaminated and disinfected, reverse osmosis systems are an ideal option for you. Just make sure to weigh all the pros and cons before investing in a water filtration system.

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