Aug. 18, 2025
Nanofiltration refers to a specialty-membrane process that rejects dissolved solutes in the approximate size range of 1 nanometer (10 Angstroms) — hence the term “nanofiltration.”
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With respect to the size and weight of solutes that nanofiltration membranes reject, NF operates in the realm between reverse osmosis (RO) and ultrafiltration (UF) : Organic molecules with molecular weights greater than 200 – 400 are rejected. Nanofiltration membranes can effectively reject, among other contaminants:
It also rejects certain soluble salts. Specifically, NF rejects dissolved salts in the range of 20 – 98 percent. Salts which have monovalent anions (e.g., sodium chloride or calcium chloride) have rejections of 20 – 80 percent, whereas salts with divalent anions (e.g., magnesium sulfate) have higher rejections of 90 – 98 percent. Transmembrane pressures are typically 50 – 225 psi (3.5 – 16 bar).
The ideal nanofiltration membrane has a very high water permeability, but the ideal permeability of solutes might be near zero or some higher value, depending on the solute and application. For example, an application may require near-zero permeability for pesticides and 50 percent permeability for calcium ions.
Typical applications of nanofiltration membrane systems include:
Like reverse osmosis membranes, nanofiltration membranes are used in separation systems employing applied pressure to effectively overcome the system’s osmotic pressure, reversing the flow of a solvent across a semipermeable membrane from an area of higher solute concentration to an area of lower concentration. This “reversed” flow, and the degree of permeability of the nanofiltration membrane, result in solutes too large to pass through the membrane remaining on the higher-concentration side of the membrane, while purer water that contains desired or acceptable solutes flows through.
Nanofiltration membranes are similar to RO membranes in another way: They are used in crossflow configurations. Crossflow helps to minimize fouling, or the accumulation of solutes that cannot pass through the semipermeable membrane against the membrane. Very simply stated, in crossflow a pressurized flow of feedwater forces lower-concentration water through the NF membrane, while the now-isolated flow of higher-concentration water moves across the surface of the membrane, carrying away the rejected salts and other impurities. The purified water is called the permeate, while the higher-concentration water is called the concentrate or reject.
Nanofiltration (NF) is a membrane treatment process primarily used to separate dissolved solutes from water.
The process of movement of solvent through a semipermeable membrane from the solution to the pure solvent by applying excess pressure on the solution side is called nanofiltration.
Nanofiltration (NF) is most commonly known for its use in drinking water purification, particularly with regard to removing salt and other effluent materials from water molecules.
Table of Contents
Introduction to Nanofiltration (NF)
Nanofiltration (NF) Principle
Nanofiltration (NF) Pore Sizes
Nanofiltration (NF) Membranes Manufacturing
Nanofiltration (NF) Process
How does Nanofiltration (NF) work?
Benefits of Nanofiltration (NF)
Advantages of Nanofiltration (NF)
Differences Between Nanofiltration, Reverse Osmosis, and Ultrafiltration
Nanofiltration vs. Reverse Osmosis
Nanofiltration vs. Ultrafiltration
Conclusion
FAQs
Nanofiltration (NF) is a popular separation technique used mainly for the purification of water.
Today, this technique is extensively used by many around the world to purify water for industrial, residential, commercial and scientific purposes. While nanofiltration (NF) technology is one of humanity’s important scientific innovations we will develop a basic understanding of the whole process here on this article.
To break down the process further, due to the presence of a membrane, large molecules of the solute are not able to cross through it and they remain on the pressurised side.
The pure solvent, on the other hand, is allowed to pass through the membrane. When this happens the molecules of the solute start becoming concentrated on one side while the other side of the membrane becomes dilute. Furthermore, the levels of solutions also change to some degree.
In essence, nanofiltration (NF) takes place when the solvent passes through the membrane against the concentration gradient. It basically moves from a higher concentration to a lower concentration.
Nanofiltration is a membrane filtration-based method that uses nanometer sized pores through which particles smaller than 10 nanometers pass through the membrane.
Nanofiltration membranes have pore sizes from 1-10 nanometers, smaller than that used in microfiltration and ultrafiltration, but a little bit bigger than that in reverse osmosis.
Pore dimensions are influence by pH, temperature and time during development with pore densities ranging from 1 to 106 pores per cm².
Nanofiltration membranes made from polyethylene terephthalate and other similar materials, are referred to as "track-etch" membranes, named after the way the pores on the membranes are made.
"Tracking" involves bombarding the polymer thin film with high energy particles. This results in making tracks that are chemically developed into the membrane, or "etched" into the membrane, which are the pores.
Membranes created from metal such as alumina membranes, are made by electrochemically growing a thin layer of aluminum oxide from aluminum metal in an acidic medium.
When the solution side (the side where the solute concentration is high) is subjected to a pressure greater than the osmotic pressure, the solvent particles on the solution side move through the semipermeable membrane to the region where the solute concentration is low. Such inverse solvent movement through the semipermeable membrane is called nanofiltration (NF).
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It is important to note that the pressure applied to the solution side must be higher than the osmotic pressure for the nanofiltration (NF) process to proceed. Osmotic pressure is a colligative property, which depends on the concentration of the solution. In water purification, the nanofiltration (NF) process is very important. Many water purifiers used today use nanofiltration (NF) in the purification process as one of the steps.
An easy experiment can be conducted by taking some freshwater and a concentrated aqueous solution. The solutions should be kept on opposite sides with a semipermeable membrane placed in between to separate the two solutions. Pressure should be applied on the side with the concentrated solution. Now this will result in water molecules moving through the membrane to the freshwater side. This basically sums up the process of nanofiltration (NF).
Some of the benefits of nanofiltration (NF) are:
This process can be used to effectively remove many types of dissolved and suspended chemical particles as well as biological entities (like bacteria) from the water.
This technique has a wide application in treating liquid wastes or discharges.
It is used in purifying water to prevent diseases.
It helps in desalinating seawater.
It is beneficial in the medical field.
Nanofiltration finds a wide range of applications in diverse industries due to its versatile nature. Some of the key applications include:
1. Drinking Water Purification
Nanofiltration plays a vital role in the purification of drinking water, removing contaminants such as pesticides, heavy metals, and organic compounds. It improves water quality, making it safe for consumption and adhering to stringent health standards.
2. Wastewater Treatment
In wastewater treatment plants, nanofiltration is employed to remove dissolved impurities and color from industrial effluents, producing treated water that can be safely discharged or reused.
3. Pharmaceutical Industry
The pharmaceutical industry utilizes nanofiltration for the separation and concentration of active pharmaceutical ingredients (APIs) and the removal of unwanted impurities during drug manufacturing.
4. Food and Beverage Industry
Nanofiltration aids in the concentration of fruit juices, desalting of whey, and the removal of unwanted tastes and odors from beverages, improving their overall quality.
5. Softening of Water
Nanofiltration can effectively soften hard water by removing calcium and magnesium ions, preventing the formation of limescale and enhancing the lifespan of household appliances.
6. Recovery of Valuable Compounds
In various industrial processes, nanofiltration enables the recovery and purification of valuable compounds, reducing waste generation and improving overall process efficiency.
To gain a better understanding of nanofiltration, it's essential to compare it with similar filtration methods:
Both nanofiltration and reverse osmosis employ semipermeable membranes, but they differ in their pore size and the types of particles they retain. While nanofiltration can remove divalent ions, reverse osmosis can eliminate monovalent ions as well, making it more suitable for desalination.
Nanofiltration and ultrafiltration are similar in some aspects, but nanofiltration can remove smaller particles and molecules due to its smaller pore size. Ultrafiltration is primarily used for separating macromolecules and colloidal particles.
As manufacturing technology advances and research progresses, the future of nanofiltration looks promising.
Researchers are continually exploring new applications and enhancing membrane properties to make nanofiltration more efficient and cost-effective.
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Nanofiltration (NF) works by using a high-pressure pump to increase the pressure on the salt side of the membrane and force the water across the semipermeable NF membrane, leaving almost all dissolved salts in the reject stream behind. While at the same time it can reduce monovalent ions by 60-80%.
Nanofiltration (NF) is a means of pulling clean water out of polluted water or salt water by pushing water through a membrane under pressure. An example of nanofiltration (NF) is the process by which contaminated water is filtered under pressure.
Nanofiltration (NF) is a water purification process that removes ions, unwanted molecules and larger particles from drinking water using a partially permeable membrane. As a result, the solute is kept on the membrane’s pressurised side and the pure solvent is allowed to pass to the other side.
The lifespan of a nanofiltration membrane depends on various factors such as the quality of the membrane, the nature of the feed water, and the operating conditions. Generally, a well-maintained membrane can last anywhere from 1.5 to 3 years.
While nanofiltration can effectively remove some bacteria and viruses, it is not an absolute barrier to all pathogens. To ensure complete removal of harmful microorganisms, additional disinfection steps may be necessary.
Nanofiltration can be cost-effective for large-scale applications when compared to some other technologies, such as reverse osmosis.
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