Invisible to the naked eye, nanofiltration is currently one of the most high-performance water treatment technologies. Used in industry, the agricultural sector, emergency situations, and the production of drinking water, it allows for the elimination of numerous contaminants while retaining some of the minerals naturally present in water.
However, this technology remains little known to the general public. Many confuse it with reverse osmosis or think it is simply a more efficient filter. In reality, nanofiltration has a very specific operating principle and meets different needs.
In this article, we will discover how a nanofiltration membrane works, what contaminants it is capable of retaining, why it preserves a portion of the mineral salts, and in which cases it constitutes a particularly suitable solution.
What is nanofiltration?
Nanofiltration is a pressure-driven membrane filtration process. Water passes through a membrane made up of extremely fine pores, on the nanometer scale, which is about a thousand times smaller than the thickness of a hair.
Thanks to this microscopic structure, the membrane acts as a selective barrier. It lets water molecules and some dissolved mineral salts pass through, while retaining numerous contaminants present in the water.
The term "nanofiltration" comes precisely from the size of these pores, which falls between microfiltration, ultrafiltration, and reverse osmosis. This intermediate position allows it to offer an excellent compromise between filtration quality, mineral retention, and energy consumption.
Contrary to popular belief, nanofiltration functions neither via chemicals nor through a disinfection process. The separation is achieved solely through the physical properties of the membrane and the pressure exerted on the water.
How does a nanofiltration membrane work?
To understand nanofiltration, it is helpful to imagine an extremely sophisticated sieve. Of course, this comparison has its limits, but it helps to visualize the general principle.
When water arrives at the membrane, several physical phenomena occur simultaneously.
- Water molecules pass through the membrane.
- Some small mineral ions also continue on their way.
- Larger organic molecules are retained.
- Numerous pesticides, PFAS, bacteria, viruses, and other contaminants remain blocked by the membrane.
Separation therefore does not depend solely on particle size. The electrical charge of the molecules also plays an important role. Certain substances that are very small are nevertheless retained thanks to electrostatic interactions between the membrane and the contaminants.
It is this dual selection—by size and by electrical charge—that makes nanofiltration unique and explains its excellent performance against many pollutants found in water resources.
Why do we call it selective filtration?
Contrary to a widespread idea, a nanofiltration membrane does not retain "everything." Its goal is not to produce completely demineralized water, but to remove a large number of contaminants while allowing some of the elements naturally present in the water to flow through.
It is for this reason that we speak of selective filtration.
In practice, every membrane has its own unique characteristics. Depending on its design and the conditions of use, certain molecules will be retained more than others. Performance can also vary depending on the pressure, temperature, or the composition of the raw water.
This selectivity is one of the main differences from reverse osmosis, which functions based on a much more restrictive membrane. We will return to this distinction a little later in the article.
What contaminants can nanofiltration retain?
One of the main advantages of nanofiltration is its ability to retain a wide range of contaminants that may be present in water. Its performance depends on numerous parameters, notably the type of membrane used, the operating pressure, and the composition of the water to be treated.
Contrary to misconceptions, there is not just one type of nanofiltration membrane. Each manufacturer develops membranes with specific characteristics in order to meet particular uses.
In general, nanofiltration is recognized for its ability to effectively reduce:
- numerous pesticides and their metabolites;
- PFAS (per- and polyfluoroalkyl substances);
- bacteria;
- viruses;
- microplastics;
- a large portion of dissolved organic matter;
- certain metals and multivalent ions;
- turbidity and suspended particles.
This versatility explains why nanofiltration is currently used in very varied sectors, ranging from the production of drinking water to the treatment of water intended for the food industry, agriculture, or humanitarian interventions.
PFAS
PFAS, sometimes nicknamed "forever chemicals," have become one of the main concerns regarding water quality. Used for several decades in numerous industrial processes and everyday products, they are particularly persistent in the environment.
Thanks to the combination of its small pore size and its electrostatic properties, nanofiltration can effectively reduce many PFAS. The exact performance varies depending on the molecules involved and the membrane used, but this technology currently ranks among the most effective solutions for treating this type of contamination.
To better understand the origin of these contaminants, you can consult our article dedicated to contaminants present in tap water in France.
Pesticides
Pesticides also constitute a family of contaminants frequently found in water resources, particularly near agricultural areas. Here again, nanofiltration presents excellent performance on many organic molecules.
The retention capacity depends mainly on the size of the molecules, their electrical charge, as well as the characteristics specific to each membrane.
Bacteria and viruses
Nanofiltration membranes also offer an excellent physical barrier against bacteria and numerous viruses. Since their size is largely greater than that of the membrane pores, they are retained when the water passes through.
This property explains why nanofiltration is used in certain applications where microbiological safety is essential, particularly for the production of drinking water in isolated environments or during relief operations.
Microplastics
Microplastics represent a relatively recent research topic. Although their size is highly variable, they are generally much larger than the pores of a nanofiltration membrane.
They can therefore be retained effectively, just like a large portion of the suspended particles present in the water.
Why does nanofiltration retain some minerals?
The question comes up very often: if nanofiltration retains so many contaminants, why does it let some minerals through?
The answer lies in the very operation of the membrane.
Not all substances dissolved in water have the same size or the same electrical charge. Certain ions, such as calcium (Ca²⁺) or magnesium (Mg²⁺), can partially cross the membrane depending on the model used and the operating conditions.
This is precisely what differentiates nanofiltration from other, more restrictive processes.
In practice, the membrane performs a genuine molecular sorting. It preferentially blocks contaminants possessing certain characteristics, while letting some of the elements naturally present in the water pass through.
It is however important to provide an essential nuance: nanofiltration does not retain 100% of minerals. Performance varies depending on:
- the type of membrane;
- the operating pressure;
- the chemical composition of the water;
- the nature of the ions present.
This is why it is more accurate to speak of a partial retention of mineral salts. This clarification is important, as it reflects the actual operation of this technology as described in scientific literature.
Which minerals are generally retained?
Depending on the membranes used, some of the minerals naturally present in the water may continue to pass through the membrane, notably:
- calcium;
- magnesium;
- potassium;
- part of the sodium.
The level of retention varies from one installation to another. It depends on both the quality of the original water and the desired performance.
This characteristic constitutes one of the main strengths of nanofiltration when it is desirable to preserve naturally balanced water while effectively reducing a large number of contaminants.
Nanofiltration or reverse osmosis: what are the differences?
Nanofiltration and reverse osmosis both rely on the principle of pressure-driven membrane filtration. They are often compared because they use high-performance membranes, but their objectives are not exactly the same.
The main difference lies in the level of filtration.
A reverse osmosis membrane is much more restrictive. It retains a vast majority of dissolved substances, including a large portion of the mineral salts naturally present in the water. Conversely, nanofiltration is designed to perform more selective filtration: it reduces numerous contaminants while letting some minerals pass through depending on the characteristics of the membrane used.
| Criteria | Nanofiltration | Reverse osmosis |
|---|---|---|
| Principle | Selective membrane filtration | Very fine membrane filtration |
| Mineral retention | Partial | Very low |
| PFAS and pesticides | Very good reduction | Very good reduction |
| Bacteria and viruses | Very good retention | Very good retention |
| Applications | Drinking water, agriculture, industry, emergency situations | Desalination, laboratory, industry, advanced purification |
No technology is universally better than the other. The choice always depends on the quality of the water to be treated, the contaminants present, and the desired goal.
Where is nanofiltration used?
Thanks to its versatility, nanofiltration is currently used in many sectors.
- Production of drinking water.
- Treatment of certain groundwater.
- Agricultural operations.
- Food industry.
- Pharmaceutical industry.
- Recycling of certain industrial water.
- Emergency situations and humanitarian interventions.
At FLX Water, this technology is integrated into several solutions developed to meet specific needs.
The FiltraLife Agricultural Solution helps improve the quality of water intended for agricultural operations to support farmers in managing their resources.
The FiltraLife Crisis Solution was designed to produce drinking water in environments where infrastructure is absent or degraded, without the need for electricity.
This technology was notably awarded a gold medal at the Concours Lépine, illustrating its innovative nature and the performance achieved in water treatment.
What are the advantages of nanofiltration?
- Effective reduction of a wide range of contaminants.
- Retention of a portion of the minerals naturally present in the water.
- Excellent performance on many pesticides and PFAS.
- Very good barrier against bacteria, viruses, and microplastics.
- Recognized technology used in many sectors.
- Adaptable to different types of applications depending on the membranes used.
Are there any limitations?
Like any water treatment technology, nanofiltration also has certain limitations.
Its performance depends strongly on the quality of the input water, the choice of membrane, the operating pressure, and the maintenance of the installation.
It therefore does not constitute a universal solution applicable to all situations. A preliminary water analysis remains essential in order to determine the most suitable technology.
Frequently asked questions
Does nanofiltration eliminate PFAS?
It allows for the effective reduction of many PFAS. Performance, however, varies depending on the molecules involved, the membrane used, and the operating conditions.
Does nanofiltration retain all minerals?
No. It lets some mineral salts pass through, but the retention rate depends on the membrane and the composition of the water.
What is the difference between nanofiltration and reverse osmosis?
Reverse osmosis is more restrictive and eliminates a larger proportion of dissolved substances, including a large portion of minerals. Nanofiltration performs more selective filtration.
Does nanofiltration eliminate bacteria and viruses?
Nanofiltration membranes constitute an excellent barrier against bacteria and numerous viruses thanks to the extremely fine size of their pores. Exact performance nevertheless depends on the system used.
Is nanofiltration used only for drinking water?
No. It is also employed in agriculture, industry, emergency situations, the treatment of certain industrial water, and many environmental applications.
Conclusion
Nanofiltration is currently one of the most advanced technologies for water treatment. Thanks to its selective membrane, it allows for the reduction of a wide range of contaminants while preserving some of the minerals naturally present.
Its ability to combine performance, versatility, and selectivity explains its growing use in many fields, from drinking water production to agricultural and humanitarian applications.
If you wish to delve deeper into the subject of water quality, we also invite you to consult our article dedicated to contaminants present in tap water, as well as our guide explaining why you should switch from bottled water to water filtration.
Sources
- U.S. Environmental Protection Agency (EPA) – Drinking Water Treatment Technologies.
- World Health Organization (WHO) – Guidelines for Drinking-water Quality.
- Scientific publications on nanofiltration membranes (Elsevier, MDPI, Water Research).
- ANSES – Quality of water intended for human consumption.
