Ultrafiltration, Nanofiltration and Reverse Osmosis

ULTRAFILTRATION, NANOFILTRATION AND REVERSE OSMOSIS FACT SHEET

What is Filtration?

Filtration is a process of removing particulate matter from water by forcing the water through a porous media. This porous media can be natural, in the case of sand, gravel and clay, or it can be a membrane wall made of various materials. Sometimes, large particles are settled before filtration; this is called sedimentation. For information on sedimentation and filtration, in general, see the Conventional Water Treatment: Coagulation and Filtration fact sheet.

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The size of materials that can be removed during filtration depends upon the size of the pores of the filter. The chart below summarizes the various separation processes relative to common materials that would be filtered out through each process. Particle filtration refers to conventional media filtration, while the other types are membrane filtrations. 

What is Ultrafiltration?

An ultrafiltration filter has a pore size around 0.01 micron. A microfiltration filter has a pore size around 0.1 micron, so when water undergoes microfiltration, many microorganisms are removed, but viruses remain in the water. Ultrafiltration would remove these larger particles, and may remove some viruses. Neither microfiltration nor ultrafiltration can remove dissolved substances unless they are first adsorbed (with activated carbon) or coagulated (with alum or iron salts).

What is Nanofiltration?

A nanofiltration filter has a pore size around 0.001 micron. Nanofiltration removes most organic molecules, nearly all viruses, most of the natural organic matter and a range of salts. Nanofiltration removes divalent ions, which make water hard, so nanofiltration is often used to soften hard water.

What is Reverse Osmosis?

Reverse osmosis filters have a pore size around 0. micron. After water passes through a reverse osmosis filter, it is essentially pure water. In addition to removing all organic molecules and viruses, reverse osmosis also removes most minerals that are present in the water. Reverse osmosis removes monovalent ions, which means that it desalinates the water. To understand how reverse osmosis works, it is helpful to understand osmosis.

Osmosis occurs when a semi-permeable membrane separates two salt solutions of different concentrations. The water will migrate from the weaker solution to the stronger solution, until the two solutions are of the same concentration, because the semi-permeable membrane allows the water to pass through, but not the salt. In the following diagram, (A) and (B) illustrate the process of osmosis.

In reverse osmosis, the two solutions are still separated by a semi-permeable membrane, but pressure is applied to reverse the natural flow of the water. This forces the water to move from the more concentrated solution to the weaker. Thus, the contaminants end up on one side of the semi-permeable membrane and the pure water is on the other side. In the diagram below, reverse osmosis is represented in (C).

What do These Three Processes Remove?

Ultrafiltration removes bacteria, protozoa and some viruses from the water. Nanofiltration removes these microbes, as well as most natural organic matter and some natural minerals, especially divalent ions which cause hard water. Nanofiltration, however, does not remove dissolved compounds. Reverse osmosis removes turbidity, including microbes and virtually all dissolved substances. However, while reverse osmosis removes many harmful minerals, such as salt and lead, it also removes some healthy minerals, such as calcium and magnesium. This is why water that is treated by reverse osmosis benefits by going through a magnesium and calcium mineral bed. This adds calcium and magnesium to the water, while also increasing the pH and decreasing the corrosive potential of the water. Corrosive water may leach lead and copper from distribution systems and household water pipes.

What Are the Advantages of Using Ultrafiltration, Nanofiltration or Reverse Osmosis to Treat Water?

All three of these membrane filtration processes are effective methods of treating water that cannot be treated using conventional treatment methods. Reverse osmosis, in particular, has been responsible for ending several nearly decade long Boil Water Advisories. For example, in , a reverse osmosis system, together with a biological treatment process, was set up to successfully treat drinking water for the Yellow Quill First Nation, which had been on a Boil Water Advisory since . The water in the First Nations community, which is located in Saskatchewan, contained high levels of organic matter, iron, manganese, ammonium and arsenic, to name a few. Besides the obvious benefit of providing safe drinking water to a community which had been under a Boil Water Advisory for approximately nine years, the reverse osmosis system (together with the biological treatment) allowed the community to treat their water using small quantities of chemicals.

A portable reverse osmosis unit was brought in to Kashechewan, a First Nations community in Ontario, in October of . The community had experienced water contamination issues for years, and in October , approximately 1,100 of the 1,900 residents were evacuated, after E. coli was found in their water. The reverse osmosis unit was brought in by the military, and could provide 50,000 litres of water each day for the residents of Kashechewan, until their water treatment plant could be fixed. The picture below compares the colour of the untreated water to that of the water after being treated with reverse osmosis.

What Are the Disadvantages of Using Ultrafiltration, Nanofiltration or Reverse Osmosis to Treat Water?

Compared with the benefits of using membrane filtration to treat water, there are very few disadvantages. If conventional water treatment processes can effectively treat the water, then constructing a reverse osmosis water treatment facility would be an unnecessary cost. But for the First Nations communities that have been on Boil Water Advisories for many years, a reverse osmosis treatment system can be a valuable investment that can provide safe drinking water for the residents.

Reverse osmosis removes a number of healthy minerals from water, in addition to the harmful minerals and particles. The removal of these minerals, including calcium and magnesium, can actually make water unhealthy, especially for people with inadequate diets and people who live in hot climates, as water can provide these necessary minerals. The addition of calcium and magnesium, as described above, can resolve these concerns.

The Safe Drinking Water Foundation has educational programs that can supplement the information found in this fact sheet. Operation Water Drop looks at the chemical contaminants that are found in water; it is designed for a science class. Operation Water Flow looks at how water is used, where it comes from and how much it costs; it has lessons that are designed for Social Studies, Math, Biology, Chemistry and Science classes. Operation Water Spirit presents a First Nations perspective of water and the surrounding issues; it is designed for Native Studies or Social Studies classes. Operation Water Health looks at common health issues surrounding drinking water in Canada and around the world and is designed for a Health, Science and Social Studies collaboration. Operation Water Pollution focuses on how water pollution occurs and how it is cleaned up and has been designed for a Science and Social Studies collaboration. To access more information on these and other educational activities, as well as additional fact sheets, visit the Safe Drinking Water Foundation website at www.safewater.org.

Did you know that our Operation Water Biology program teaches students about biological water treatment - a more effective and environmentally friendly way to treat drinking water? In the Operation Water Biology program students build a model of a biological water treatment plant and learn about chlorine, chloramine, ammonia, and iron in a hands-on manner. Please help us send more Operation Water Biology kits to schools! Please chip in $5 or donate $20 or more and receive an Official Donation Receipt for Income Tax Purposes - or donate $170 to provide a school with an Operation Water Biology kit.

Ultrafiltration membrane treatment is an advanced water treatment process that has gained significant popularity in recent years due to its effectiveness in removing a wide range of contaminants from water. Whether you're curious about how ultrafiltration membranes improve water quality or seeking solutions for industrial water treatment, understanding ultrafiltration can help you make informed decisions about your water treatment needs.

In this comprehensive guide, we'll explore what ultrafiltration is, how it works, its benefits, and how it compares to other filtration methods. We'll also delve into the types of ultrafiltration membranes, what they remove, and how to maintain an ultrafiltration system. By the end of this article, you'll have a clear understanding of this powerful water treatment technology and its applications.

What is Ultrafiltration (UF)?

Ultrafiltration, often abbreviated as UF, is a hollow-fibre membrane-based separation process used in water treatment. It's a type of filtration that uses a semi-permeable membrane with very fine pores to separate water from suspended solids, colloids, and high molecular weight substances.

Depending on the type of hollow-fiber UF system,  a vacuum applied to the inside of the membrane to suck the feed water to the inside of the membrane through many microscopic pores, results in a clean filtered water. In a pressurized UF system, the water is pressurized and pumped through the hollow fibers to force the water through the membranes. Both hollow fiber UF membranes effectively remove particles, bacteria, viruses, and other contaminants. This results in high-quality water suitable for various applications, from drinking water production to industrial processes.

What sets ultrafiltration apart is its ability to consistently deliver superior water quality regardless of fluctuations in raw water conditions. Additionally, ultrafiltration can serve as an excellent pretreatment step for reverse osmosis systems, when a higher quality water is required. The UF system helps to enhance the longevity of an RO system by removing particles that could potentially foul the RO membranes.

Key features of hollow fiber ultrafiltration include:

• Pore sizes typically ranging from 0.01 to 0.1 microns
• Ability to remove particles, bacteria, and some viruses
• Low energy consumption compared to other membrane technologies
• Minimal use of chemicals in the treatment process
• Consistent water quality output regardless of influent variations

Ultrafiltration water treatment has become increasingly popular due to its efficiency, reliability, and ability to produce high-quality water regardless of source water fluctuations.

Is There A Difference Between Filtration and Ultrafiltration?

While both filtration and ultrafiltration aim to purify water, there are significant differences between the two processes. Traditional filtration typically relies on physical barriers, such as sand or activated carbon, to trap larger particles and some dissolved substances. In contrast, ultrafiltration employs advanced membrane technology with much smaller pore sizes, allowing for the removal of not only suspended solids but also bacteria, viruses, and other microscopic contaminants. Reverse osmosis nanofiltration systems can filter out particles as small as 0.01 microns, providing a higher level of water purity compared to conventional filtration methods. This makes ultrafiltration particularly effective for producing high-quality drinking water and treating industrial process water. Additionally, ultrafiltration systems often require less frequent backwashing and maintenance than traditional filtration systems, resulting in improved operational efficiency and cost-effectiveness.

• Pore size: Traditional filtration methods typically use larger pore sizes, ranging from 1 to microns. Ultrafiltration membranes have much smaller pores, and can filter out particles between 0.01 and 0.1 microns.
• Contaminant removal: Standard filtration is effective at removing larger particles and some microorganisms. Ultrafiltration can remove not only these contaminants but also smaller particles, bacteria, and even some viruses.
• Water quality: Ultrafiltration produces higher quality water than traditional filtration methods due to its ability to remove smaller contaminants of molecular size
• Applications: While both methods are used in water treatment, ultrafiltration is often employed in more demanding applications where higher water purity is required.

How Does Ultrafiltration Work?

Understanding how ultrafiltration works is key to appreciating its effectiveness in water treatment. Ultrafiltration is a pressure-driven membrane filtration process that effectively removes contaminants from water. The heart of an ultrafiltration system is the semi-permeable membrane with pores typically ranging from 0.01 to 0.1 microns in size. As water is forced through these tiny pores under pressure, particles larger than the pore size are trapped, while water molecules and smaller dissolved substances pass through.

This process effectively removes suspended solids, bacteria, viruses, and other microorganisms from the water. Ultrafiltration water filters can be implemented in two main types of systems: at the point-of-use (POU) systems, which treat water where it is used, and point-of-entry (POE) systems, which treat all the water entering a building.

The ultrafiltration process typically involves several stages:

1. Prefiltration: Before water enters the ultrafiltration system, it typically passes through a prefilter to remove larger particles that could potentially damage the UF membrane.
2. Pressure application: Depending on the type of ultrafiltration membrane, a vaccum is applied to suck the water through the membrane our the water is pressurized and forced through the ultrafiltration membrane.
3. Membrane separation: As water passes through the UF membrane, contaminants larger than the membrane's pore size are trapped on the surface or within the membrane structure.
4. Permeate collection: The filtered water, known as permeate, passes through the membrane and is collected for use or further treatment.
5. Concentrate removal: Contaminants that are too large to pass through the membrane accumulate on the feed side, forming a concentrate that is periodically flushed from the system.
6. Backwashing: To maintain efficiency, ultrafiltration systems periodically reverse the flow of water to clean the membrane surface, a process known as backwashing.

The UF membrane acts as a physical barrier, effectively removing:

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• Suspended solids
• Bacteria
• Protozoa
• Some viruses
• Colloids
• High molecular weight organic compounds

This process results in clear, high-quality water suitable for various applications, from drinking water to industrial use.

Types of Ultrafiltration Membranes

Ultrafiltration membranes come in various configurations, each designed to suit specific applications and water treatment needs. The choice of membrane type can significantly impact the efficiency and effectiveness of the ultrafiltration process. Here are the main types of UF membranes used in water treatment:

1. Immersed Hollow Fiber Membranes

This type of UF membrane consists of bundles of hollow fibers with microscopic pores. Water flows either inside the fibers and out through the walls (inside-out configuration) or outside the fibers and in through the walls (outside-in configuration). Hollow fiber modules offer a high surface area to volume ratio, making them efficient and compact, which is particularly advantageous for large-scale municipal water treatment plants.

• Excellent for handling high solids content
• Commonly used in municipal water and wastewater treatment

2. Pressurized Hollow Fiber Membranes

These hollow fiber membranes operate by feeding pressurized water to the module and into the membrane fibers. Once inside the fibers the pressure makes the filtered water to flow (permeate) across the membrane wall and out of the module. The suspended solids, microorganisms and particulate organics accumulate inside the fiber.  At the end of the production cycle, the pollutants trapped inside the membrane fibers are removed by using a forward flush with feed water. Periodically, a backwash is performed to further clean the fibers after each production cycle.

• Excellent at handling raw water fluctuation without effecting the water produced
• Commonly used for drinking water, industrial process water and tertiary filtration

3. Spiral Wound Membranes

These modules are made of flat sheet membranes wrapped around a central permeate collection tube. Feed water flows between the membrane sheets, and filtered water spirals inward to the central tube. Spiral wound modules are compact and provide higher quality water than traditional filters.

• Provide high quality permeate water quality
• Often used in food and beverage industries

4. Tubular Membranes:

These membranes consist of tubes with porous walls, typically made of polymeric materials. Water flows through the tubes, and the UF membrane filter action occurs as it passes through the porous walls. Tubular membranes are excellent for handling high-solids content and are easy to clean, making them ideal for industrial applications with challenging feed streams.

• Tube-shaped membranes housed in a larger tube
• Frequently used in industrial wastewater treatment

5. Plate and Frame Membranes:

This configuration uses flat sheet membranes stacked between support plates. Feed water flows between the membranes, with permeate collected from the edges. Plate and frame modules are known for their durability and ability to handle high pressures, making them suitable for specialized industrial applications.

• High pressure tolerance and suitable for viscous fluids
• Often used in specialized industrial applications

Each type of ultrafiltration membrane has its strengths, and the choice depends on factors such as the specific application, feed water quality, desired output, and operational considerations.

What Are The Benefits of Ultrafiltration?

Ultrafiltration offers numerous advantages in water treatment, making it an increasingly popular choice for municipal  and industrial applications. Hollow fiber UF membranes provide a physical barrier to suspended solids and pathogens to consistently produce a high-quality, low-turbidity, and low-SDI effluent.

Here are the key benefits of implementing an ultrafiltration system:

1. Pressurized or immersed membranes to suit the site requirements.
2. Greater output in the same footprint and helps reduce capital and lifecycle costs for the application.
3. Physical UF barrier provides consistent high-quality effluent exceeding stringent regulatory requirements through virtually any change in raw-water quality.
4. Low lifecycle cost optimized through extended membrane life and low energy and chemical use.

These benefits make ultrafiltration an attractive option for various water treatment applications, from municipal water supplies to industrial process water.

What Does Ultrafiltration Remove?

Ultrafiltration is highly effective at removing a wide range of contaminants from water. Here's a breakdown of what an ultrafiltration water filter can typically remove:

1. Particulate matter:

• Suspended solids

• Colloids

• Turbidity

2. Microorganisms:

• Bacteria (99.99% removal)

• Protozoa (including Giardia and Cryptosporidium)

• Many viruses

3. Organic compounds:

• High molecular weight organics

• Some humic substances

4. Inorganic compounds:

• Some heavy metals, when bound to organic matter or particles

5. Other contaminants:

• Algae

• Some parasites

It's important to note that while ultrafiltration is highly effective at removing many contaminants, it does not remove contaminants like dissolved salts, organic molecules, or ions smaller than the pore size. Additional treatment methods like reverse osmosis or ion exchange may be necessary for these.

How Do You Maintain An Ultrafiltration System?

Proper maintenance is crucial for ensuring the longevity and efficiency of an ultrafiltration system. Here are some key maintenance practices:

1. Regular backwashing: Perform backwashing as recommended by the manufacturer to remove accumulated particles from the membrane surface.
2. Chemical cleaning: Periodically conduct chemical cleaning to remove fouling that backwashing can't address. This typically involves using specialized cleaning solutions.
3. Integrity testing: Regularly test the integrity of the UF membranes to ensure they're functioning correctly and haven't been compromised.
4. Pretreatment maintenance: Keep pretreatment systems (if present) in good working order to protect the UF membranes from excessive fouling.
5. Monitor operating parameters: Regularly check and record key parameters like pressure, flow rate, and water quality to detect any performance issues early.
6. Replace membranes: UF membranes have a finite lifespan and will need replacement eventually. Follow manufacturer guidelines for replacement schedules.
7. Operator training: Ensure that system operators are well-trained in the proper operation and maintenance of the ultrafiltration system. By following these maintenance practices, you can maximize the performance and lifespan of your ultrafiltration system, ensuring consistent, high-quality water production.

By following these maintenance practices, you can maximize the performance and lifespan of your ultrafiltration system, ensuring consistent, high-quality water production.

Address Ultrafiltration With Veolia's ZeeWeed* Ultrafiltration Hollow-Fiber Membranes

When it comes to implementing ultrafiltration in your water treatment process, Veolia's ZeeWeed* Ultrafiltration Hollow-Fiber Membranes offer a cutting-edge solution. These advanced membranes are designed to provide superior performance, reliability, and efficiency in a wide range of applications.

Key features of Veolia's ZeeWeed* membranes include:

• High-quality water production
• Excellent removal of particulates, bacteria, and viruses
• Low energy consumption Robust design for long-term durability
• Versatility for various water treatment applications

Whether you're looking to upgrade your existing water treatment system or implement a new ultrafiltration solution, Veolia's ZeeWeed* membranes can help you achieve your water quality goals efficiently and effectively.

To learn more about how Veolia's ZeeWeed* Ultrafiltration Hollow-Fiber Membranes can benefit your water treatment process, contact our team of experts today. We're here to help you design and implement the ideal ultrafiltration system for your specific needs.

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