Reverse Osmosis vs Nanofiltration: Difference + Which to Use
Written by: Alexandra Uta // Last Updated: Jun 16, 2023
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Despite sharing many similar characteristics, reverse osmosis and nanofiltration are actually quite different.
For one, although they may rely on similar principles, they don’t filter the same kinds of contaminants.
You might be wondering what the exact differences between the two are, and which is better in the end. In that case, read on to find out.
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Key Takeaways
- Both reverse osmosis and nanofiltration use membranes with fine pores to remove contaminants from water. But RO membranes have much smaller pores (0.0001 microns) than nanofiltration membranes (0.001-0.01 microns) so they are more effective.
- Nanofiltration is great for removing microorganisms, suspended solids, and organic matter from water. RO is ideal if you want to target ions such as lead, chromium, or fluoride.
- While reverse osmosis water purification is much more powerful at removing harmful contaminants, it is slower, it produces wastewater, and often it’s more expensive.
What Is Reverse Osmosis (RO)?
Reverse osmosis is a popular approach to filtering water which relies on a thin, semipermeable membrane. Water is pushed through this membrane at high levels of pressure, and only water molecules are able to pass through the tiny membrane pores. Almost pure water flows out on the other end of the membrane, while all contaminants are left behind and sent away with the reject water stream.
For home use, reverse osmosis systems usually come in the shape of countertop and under sink units. These feature several other filter stages before and after the reverse osmosis membrane for additional contaminant removal.
What Is Nanofiltration (NF)?
Some people confuse reverse osmosis with nanofiltration because they are somewhat similar at their core. Nanofiltration also relies on a membrane with very fine pores. However, those pores are not tiny enough to reject any water impurities. Many elements might still make it through the membrane of a nanofiltration system. Nanofiltration also doesn’t require pressure as high as reverse osmosis does. More on the differences between reverse osmosis and nanofiltration below!
By the way, most nanofiltration systems also feature additional filter stages.
Difference Between Reverse Osmosis and Nanofiltration
So what’s the difference between reverse osmosis and nanofiltration?
For one, the two processes are quite different in what contaminants they can remove from water and how they do it. Reverse osmosis is generally considered a more thorough method of filtration in comparison, but there’s more…
Contaminant Reduction
Nanofiltration can remove the following impurities and contaminants from water:
- Bacteria
- Viruses
- Cysts
- Suspended solids
- Organic matter
- Some salts and other ions
Reverse osmosis is much more thorough. It can address all of the above, but it doesn’t only remove some salts/ions but pretty much all of them, such as:
- Heavy metals including lead, chromium 6, mercury, and cadmium
- Fluoride
- Sodium
- Nitrates
As great as reverse osmosis is, it also has a major disadvantage. The membrane is sensitive to certain chemicals, requiring that they be removed from the water beforehand. This is why most reverse osmosis systems come with one or more pre-filtration stages – so that the membrane doesn’t clog up or gets damaged in any other way. Prime examples are sediments (removed with a sediment pre-filter) and chlorine (removed with a carbon pre-filter).
Nanofiltration also uses pre-filtration in many cases. This is important because the pores of the membrane are fine enough that they, too, can get clogged up.
Speaking of that, how big are the pores on those membranes exactly? With nanofiltration, they are usually around 0.001-0.01 microns in size. With reverse osmosis, on the other hand, they are just 0.0001 microns. As you can see, the pores on a reverse osmosis membrane are much smaller and therefore can get clogged up much faster. On the upside, they can reject more contamination.
Bottom line: If you have lots of harmful salts and other ions in your water, you want to use reverse osmosis in order to get rid of them and get access to water that is much healthier.
| Method | Pore Size | Impurities Removed |
|---|---|---|
| Microfiltration | 0.1-10 Microns | Sediments and Other Suspended Solids, Bacteria |
| Ultrafiltration | 0.01-0.1 Microns | Sediments and Other Suspended Solids, Bacteria, Larger Viruses |
| Nanofiltration | 0.001-0.01 Microns | Sediments and Other Suspended Solids, Bacteria, Viruses, Organic Compounds |
| Reverse Osmosis | 0.0001 Microns | Sediments and Other Suspended Solids, Microorganisms, Organic Compounds, Dissolved Ions |
Wastewater
Another thing to consider about reverse osmosis is that it also wastes some water in the process. This is unavoidable, it’s just how reverse osmosis works. Still, it’s often possible to greatly reduce the amount of wastewater by using pumps.
Filtration Speed and Water Storage
Both reverse osmosis and nanofiltration are pretty slow. However, reverse osmosis is noticeably slower. So much, in fact, that reverse osmosis systems always come with an integrated storage tank for convenience or pumps to increase filtration speed. Otherwise, you would have to wait too long for fresh water to be available every time you want to drink. Things are not too different on the nanofiltration front. Many nanofiltration systems also rely on a storage tank.
Installation Requirements
Reverse osmosis systems are typically more difficult to install and maintain. They have more components and you also need to consider the storage tank – although you would also need to do that for a nanofiltration system. With reverse osmosis, you also have to account for a wastewater line, among other things.
Cost
Point-of-use reverse osmosis systems tend to cost more money, around $200-500, due to their higher complexity. That said, nanofiltration systems aren’t very cheap either.
If you’re looking for a solution that’s easy on your budget, you would probably gravitate towards nanofiltration, though. Just know that there aren’t that many systems available on the market.
Similarities
Now that we’ve covered the main differences between nanofiltration and reverse osmosis, let’s take a look at some of the similarities between the two processes.
Pre-Treatment Required
In both cases, pre-filtration is required to prevent the filter element from clogging up. This usually comes in the form of one or more sediment pre-filter stages. These are designed to remove large contaminants, leaving the reverse osmosis or nanofiltration membrane to deal with the smaller ones.
For RO membranes, it’s also important to eliminate any chlorine content, since it has shown to cause irreversible damage. This is usually done using activated carbon.
Water Pressure
You also need high pressure in both cases, although reverse osmosis is much more demanding in this regard. 60-80 psi are ideal here. Nanofiltration needs around 50 psi.
Applications
Both filtration methods are used domestically for drinking water treatment and in industrial applications. Examples are:
- Dairy industry
- Maple syrup concentration
- Dye concentration
- Wastewater treatment
- Municipal water purification
- Seawater desalination (RO only)
Factors Affecting Reverse Osmosis and Nanofiltration Performance
If you want to get the best performance out of your reverse osmosis or nanofiltration water system, here are a few things you need to keep in mind.
- Pressure level: You need to ensure that you can supply an adequate amount of pressure for the system to work correctly
- Pre-filtration: The better your pre-filtration setup is, the better the performance of your main system is going to be and the longer it’ll last
- Maintenance frequency: You need to replace both RO and nanofiltration membranes frequently enough to ensure that they don’t get clogged and operate at an optimal level
Further Reading:
What Are the Pros and Cons of Using Nanofiltration vs Reverse Osmosis
Nanofiltration Pros
- Effectively deals with a wide range of contaminants
- Nanofiltration membrane is less sensitive
- No wastewater
- Faster filtration than RO
- Often less expensive
- Requires less pressure than reverse osmosis
Nanofiltration Cons
- Requires pre-filtration of sediments to prevent the nanofiltration membrane from getting clogged
- May require a storage tank
- Not nearly as effective as RO
Reverse Osmosis Pros
- Most thorough method of water purification available on the market
- For the cleanest of drinking waters
- Greatly improves water smell and taste
Reverse Osmosis Cons
- Requires high pressure for optimal performance
- More expensive than nanofiltration
- Removes some healthy elements like minerals
- Produces wastewater (usually requires drain connection)
- Slow
Nanofiltration vs. Reverse Osmosis – So Which Is Better?
So, nanofiltration vs reverse osmosis – which is better?
Truth be told, it’s hard to say which of the two is better. Both filtration methods are designed to address different issues and have their own applications. If you want to be as thorough as possible, you should go with reverse osmosis. However, that might be overkill in some cases.
The best way to be sure is to have your water professionally tested so that you will know exactly what kinds of contaminants you’re dealing with. That way you can know which of the two methods would be ideal for your water conditions. As mentioned before, nanofiltration addresses most microorganisms, suspended solids, and organic matter. For heavy metals and other dissolved ions, you should definitely go with reverse osmosis.
What About Micro and Ultrafiltration?
The main difference between microfiltration, ultrafiltration, and nanofiltration is the size of the pores on the membrane. Nanofiltration has the finest pores of the three. It’s the only thing that comes close to reverse osmosis in this regard. Ultrafiltration (0.01-0.1 micron) and microfiltration (0.1-10 micron) are useful when you’ve got larger contaminants to deal with – think certain viruses, bacteria, suspended solids.
If you have any questions about the difference between nanofiltration and reverse osmosis please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
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