Nanofiltration: Pores, Membranes, Systems, and Water Treatment

Nanofiltration is the process of filtering the particles within the water that are smaller than 0.001 microns. The term nanofiltration was coined in 1984 by Dr. Peter Eriksson, which set the basis for the theory – one which was later further developed by John E. Cadotte.
The nanofiltration process is done by using nanofiltration membranes, which are filters with 0.001 pore sizes. Any contaminant of a larger size will not pass through the membrane, rendering the water clean.
Nanofiltration is essential in water treatment, as it removes any potential contaminants. If the water has received heavy chloride treatment, has a high level of hardness, or includes organic contaminants (bacteria or viruses), they will be filtered out.
Several companies offer nanofiltration systems, such as Aquatech, Koch Membrane Systems Inc., the Dow Chemical Company, ZeroWater, and Zwitterco. Most of these companies, aside from nanofiltration systems, also offer ultrafiltration and reverse osmosis systems.

How Does NanoFiltration Work?

Nanofiltration is a process that, in terms of molecular rejection, lies between reverse osmosis and ultrafiltration. Nanofiltration uses nanofiltration membranes, which can catch organic molecules of small sizes that have not yet dissolved in the water. Nanofiltration is often used in the process of turning hard water into soft water.
A nanofiltration system uses several basic parts: the feed pump, the membrane, the pipes, and the cleaning system. These parts work together to soften the water, remove heavy metal particles, and reduce salt content in the water.

What Is a Nanofiltration Membrane?

A nanofiltration membrane is a filter with a pore size of 0.001 microns which has the ability to remove almost every virus, organic molecule, as well as a variety of salts and organic matter. Nanofiltration membranes can be either porous or dense. Nanofiltration membranes are different from other membranes, as they capture smaller particles contaminating the water.
Nanofiltration membranes can have small pores, larger free spaces, and nanovoids. These nanovoids can capture particles as small as 0.001 microns, filtering out smaller organisms that ultrafiltration cannot handle. A good nanofiltration membrane can last up to 5 years.

What Is the NanoFiltration Process?

The nanofiltration system works by pressuring water into a filter, separating the impurities from the water. Here are the main steps of the nanofiltration process:

1. Water collection: The water is collected in a tank and prepared to be filtered. It will be directed under pressure towards the filters.
2. The filtration stage: Depending on how polluted the water is, it may have to pass through several filters. If the chlorine levels are high, it will first have to pass through a carbon filter before going through the nanofiltration membrane. This will protect the nanofiltration system from wear.
3. The mineralization stage: Some nanofiltration systems may take the filtered water through a mineral bed as well. This will replenish the water with the minerals that were lost during filtration.

With the water filtered, it will now make its way to the container or the pipeline. Depending on the pollution level before filtration, it may or may not be consumable.

What Are the Types of NanoFiltration Membranes?

Nanofiltration membranes come in two types: spiral and tubular.

1. Spiral Membranes

Spiral membranes are filters that take a spiral shape. These membranes feature filter material placed between mesh spacers. In the end, the material is wrapped around a small tube. NXfiltration is a popular choice in terms of spiral membranes.
Spiral membranes have a higher density compared to tubular membranes, which means that they can cover larger surfaces. Spiral membranes are cheap, making them suitable for people on a budget. They are also more sensitive to pollution. The brand Alfa Laval offers spiral nanofiltration membranes, for a variety of applications.

2. Tubular / Straw Membranes

Tubular/straw membranes are a good choice for homes that get highly contaminated water. They can filter viscous liquids with a high level of sediments. Usually, tubular membranes are made either from plastic or stainless steel and are cost-effective. These membranes are resistant to pollution. Lenntech is a popular company choice for tubular membranes.
Tubular membranes are often an advantageous choice compared to spiral membranes as they are more durable. The product itself is not cheaper, but since it mustn’t be replaced as often, it can help your budget in the long run.

What Is the Membrane Structure in the Case of Nanofiltration?

The structure of the membrane for nanofiltration falls between an ultrafiltration membrane and a reserve osmosis one. The nanofiltration membranes are negatively charged so that they can efficiently dissolve ions.
Parts of a nanofiltration membrane include a polymer film, an osmotic proprietary membrane layer, polysulfone layer, and polyester non-woven material. Nanofiltration water treatment membranes are made from polyethylene terephthalate and metals. These will come together to form a polymer film. Other materials used for nanofiltration membranes include cellulose acetate and polyamide.
Nanofiltration membranes are very lightweight, to the point where they hardly weigh anything. The weight cut-off of nanofiltration membranes is around 0.5-2 kDa.
Nanofiltration membranes can last as much as 5 years, after which you will be required to replace them. If you get the membrane from a reputable company, the lifespan will go past that range. The contamination level of the water will also determine the lifespan of nanofiltration membranes.
Nanofiltration membranes often have high endurance and can withstand most chemicals in the water. They do have a sensibility to water, in which case the association with a carbon filter is also required.

What Are NanoFiltration Membranes Made of?

Nanofiltration membranes are usually made using thin films of polymers. These films are made using the following materials:

• Polyethylene terephthalate: Also known as “track-etch” membranes, this covers the polymer film with high-energy particles.
• Metals (i.e., aluminum): These membranes are made in an electrochemical manner, by growing aluminum oxide in a thin layer.

What Is the Operating Pressure Range for Nanofiltration?

The operating pressure range for nanofiltration is 5-20 bar (200-600 PSI). This pressure is important, as it separates the contaminants from the water in a quick manner. As the membrane rejects the molecules under the pressure, only pure water will pass through the system.

What Are the Advantages of NanoFiltration?

Nanofiltration comes with several advantages, including:

1. No Chemicals: With the nanofiltration elements, no chemicals are used to purify the water. The resulting water will be pure, with no further additions.
2. Small Contaminants Are Removed: Nanofiltration membranes have pores that can capture microorganisms as small as 0.001 microns. This means that organic elements, viruses, and valence ions are filtered out from the water. This makes nanofiltration more efficient compared to ultrafiltration systems.
3. Heavy Metal Reduction: Tap water often has heavy metal particles such as lead. These particles are completely removed by passing the water through the water filter.
4. Softens Hard Water: Hard water is caused by minerals such as calcium and magnesium. Nanofiltration membranes can capture these minerals, turning hard water into soft water.
5. Dangerous Contaminants Are Removed: Contaminants such as arsenic and ammonium are also removed from the water. This makes nanofiltration an efficient option for water near nuclear plants.

What Are the Disadvantages of NanoFiltration?

Nanofiltration systems also come with several disadvantages, including:

1. Water Loss: As water is sent through the filter using pressure, highly polluted water will be discarded along with the contaminants. This can lead to a loss of water.
2. High Energy Consumption: Nanofiltration can consume between 0.3 and 1 kWh/m³. This means nanofiltration requires more energy compared to an ultrafiltration system.
3. Limited Retention for Some Contaminants: Nanofiltration has limited retention for contaminants that are soluble in water. Unless they are absorbed by other particles, univalent ions and salt may have limited retention.
4. Membranes are Expensive: As compared to reverse osmosis membranes, nanofiltration membranes are more expensive.
5. Chlorine Sensitive: Nanofiltration may filter out chlorine, but it is also sensitive to it. This applies mostly to free chlorine. If the chlorine concentration is high, using bi-sulfite treatments and carbon filters is highly recommended.

What Are the Applications of Nanofiltration?

Nanofiltration is used mainly for separating monovalent from divalent/multivalent ions. For this, you use water filters. To answer the question “what is a water filter,” it is a membrane that collects impurities from the water. Nanofiltration systems are applied for the following processes in the industry of water:

1. Sulfate Removal from Seawater: Seawater has high amounts of sulfates. Nanofiltration has the ability to selectively remove them. This is important because it prevents scaling in water operations from oilfields.
2. Organic Matter Removal from surface Water: Surface water may contain high amounts of natural organic matter. Nanofiltration systems may be used to remove those contaminants.
3. Brine Recovery: A nanofiltration membrane can capture high amounts of sulfate, only allowing the sodium chloride ions to go through. This allows for brine recovery occurring in industrial processes.
4. Other than water treatment, nanofiltration also has applications in pharmaceuticals, bulk chemistry, oil and petroleum, essential oils, and medicine.

What Can Nanofiltration Filter from Water?

Nanofiltration removes a variety of contaminants from the water, including:

1. Organic Molecules: The process of nanofiltration may remove organic molecules and macromolecules from the water. This includes compounds such as benzene, methylene chloride, pesticides, bacteria, and many more.
2. Natural Organic Matter: Natural organic matter can be removed through nanofiltration. This includes nitrates and organic matter that is larger than 0.001 microns in size.
3. Heavy Metals: Particles such as lead can be filtered out from the water by using the nanofiltration system.
4. Salts: Salts are also removed in the process of nanofiltration. This includes sulfates and chloride salt that is often present in tap water.
5. Viruses: Nanofiltration removes nearly every virus from the water. Only viruses that are smaller than 0.001 microns may pass through the membrane.

Nanofiltration filters are 40% efficient in eliminating monovalent ions such as Cl-, K+, etc., and 80-85% efficient in eliminating bi- or tri-valent ions like Mg2+, Ca2+, Mg2+, etc.

Can NanoFiltration Remove TDS?

Yes, nanofiltration can remove up to 89% of TDS in the water as well as 98% of the total hardness. TDS stands for total dissolved solids. Removal of TDS is important in water treatment because it rids the water of excessive salts and minerals. Not only will it protect the person’s health in the long run, but it will also protect home appliances that can be damaged by those minerals. Multiple levels of dissolved ions may be filtered with a nanofiltration system. At the same time, nanofiltration systems are efficient in maintaining a high flux even on low power consumption. This will depend on the quality of the membrane, as well as the reliability of the manufacturer.

Does NanoFiltration Filter Viruses and Organisms from Water?

Yes, nanofiltration can filter out organisms as small as 0.001 microns from the water. This means that almost every virus (a success rate of nearly 100%) can be filtered out of the water, rendering it healthy. Only organisms that are smaller than 0.001 microns may have the ability to escape the nanofiltration system. Smaller viruses may only be caught by reverse osmosis.
The age of the nanofilter may also determine whether it can catch the virus or not. Old filters may no longer be able to catch smaller microorganisms. This is why it is recommended to change the filters every few years.

Does NanoFiltration Remove Minerals from Water?

Along with viruses and bacteria, nanofiltration also removes certain natural minerals in the water. Some of these minerals are divalent ions, which are responsible for hard water. Nanofiltration does not remove the components that are already dissolved in the water.
If your filter is getting older, then you might want to consider replacing it. The filter’s ability to remove minerals may fade over time. This can cause the reappearance of hard water, as the minerals are passing through the filter.
Healthy minerals will also be eliminated alongside the harmful ones. A well-functioning filter may also prevent magnesium from passing through. This is why the use of a reverse osmosis system that takes the water through a calcium and magnesium bed is recommended.

Does NanoFiltration Remove Calcium?

Yes, nanofiltration removes calcium from the water. Certain nanofiltration systems take the water through a calcium and magnesium bed once the unhealthy organisms are filtered out. This is not always the case, which is why prior research is always due.
Calcium sediments are bigger, which is why even an older nanofiltration system should be able to remove calcium from the water. The amount will mostly depend on the hardness of the water.

Does NanoFiltration Remove Chloride?

Yes, nanofiltration removes chloride from the water. Nanofiltration has 78%-95% efficiency in removing chloride from the water. This will depend on the quality and age of the nanofiltration membrane as well as the reputability of the company.
Chloride is a substance that dissolves in water, so an old membrane might not be able to filter out all the chloride. Regular checkups are recommended to ensure the nanofiltration system is in peak shape.

What Is the Difference between NanoFiltration and Ultrafiltration?

The main difference between ultrafiltration and nanofiltration is that ultrafiltration filters have pores sized 0.01 microns, whereas nanofiltration, have 0.001 microns. The second difference is that while viruses may remain in the water after ultrafiltration, most of them are removed using nanofiltration. Lastly, while nanofiltration can filter some divalent ions, ultrafiltration does not have that ability unless it has been dissolved or coagulated.

What Is the Difference between NanoFiltration and Reverse Osmosis?

Nanofiltration membranes have pore sizes of 0.001 microns whereas reverse osmosis has them around 0.0001 microns. Also, with nanofiltration, certain dissolved minerals may pass through the semipermeable membrane, whereas reverse osmosis removes all of them. This is why reverse osmosis passes the water through a mineral bed after filtering it. Lastly, while nanofiltration may not be able to filter out all viruses, reverse osmosis removes all of them. The water resulting after reverse osmosis is pure, with no contaminants whatsoever.

How Much Does Nanofiltration Cost?

The cost of nanofiltration depends on the size of the nanofiltration water systems. If the system is at 100 GPM, nanofiltration can cost $250,000. A small, home-sized filter can cost as much as $30. Bigger systems, going from 300 GPM upward, can cost $2-$4 million. It depends on the company.
ZeroWater offers a cost-effective alternative in their 5-Stage Replacement Filter. The Zwitterco organic filters are slightly more expensive but have a longer life in comparison to other products. EconoPure’s “EconoPure™ Water System” has also grown in popularity, with their nanofilters offering osmotic water quality.

What Is Micron for Ultrafiltration Systems?

A micron is a unit of length that is equal to one-millionth of one meter or one-thousandth of one millimeter. Micron is short to one micrometer. Micron in water filters is essential to know, as it can tell you exactly what kind of particles will be filtered by these systems.
Each water filter has different measurements. Ultrafiltration filters measure 0.1 microns, nanofiltration filters measure 0.001 microns, and reverse osmosis filters measure 0.001 microns. Nanofiltration systems use microns to determine what viruses they may filter, as well as particles – dissolved or not.