What is membrane filtration ?
Membrane filtration is a physical separation method characterized by the ability to separate molecules of different sizes and characteristics. Its driving force is the difference in pressure between the two sides of a specialized membrane. Membrane technology enables you to bring down overall production costs, and boost product quality at the same time. Alfa Laval’s experience in membrane filtration dates as far back as 1965, and we are pleased to share this expertise with you.
Cross-flow filtration VS Dead-end filtration
Membrane filtration can be either dead-end filtration or cross-flow filtration.
Cross-flow filtration provides significant built-in advantages over dead-end filtration. Because the liquids being processed flow continuously across the membrane, there is no filter cake that can lead to fouling and uneven flow.
This makes it possible to operate a continuous, automated filtration process that results in a consistent, controllable product quality. No filter aids are needed, and the membranes have an extended lifetime.
Almost all industrial membrane filtration is carried out as cross-flow filtration, where the liquid being filtered flows parallel to the membrane at high velocity and under pressure.
How does membrane filtration work?
Membrane filtration as a physical separation process
Membrane filtration is a physical separation process in which the driving force is the difference in pressure between the two sides of a specialized membrane. This process is characterized by the ability to separate molecules of different sizes and characteristics.
Almost all industrial membrane filtration systems operate in cross-flow filtration mode, where the liquid being filtered flows parallel to the membrane at high velocity and under pressure.
Membranes as a selective physical barrier
In its most basic terms, membrane filtration involves passing a single feed stream through a membrane system that separates it into two individual streams, known as the permeate and the retentate. The membrane that separates them is a physical barrier with highly specialized characteristics - a barrier that only certain selected components in the feed stream can pass through based on molecular size and properties.
Membrane pore size and pressure-driven filtration
The pores of such membrane material are so small that they are measured in Angstrom (10-10 m), and pressure is required to force the liquid through them. In fact, the pores in the membranes used for nanofiltration and reverse osmosis are so small that they cannot be seen even with a scanning electron microscope.
Watch the video to learn how reverse osmosis supports yeast production—explained by an Alfa Laval membrane development engineer.
What are the different types of membrane filtration?
There are four commonly accepted types of membrane filtration. These are defined on the basis of the size of particles and molecules they separate from the feed liquid. The four types of membrane filtration are known as reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF), listed in order of increasing membrane pore size.
Alfa Laval offers both flat sheet membranes and spiral wound membranes covering all four membrane filtration technologies, providing flexible and reliable solutions across a wide range of filtration and separation needs.
What is reverse osmosis (RO)?
Reverse osmosis (RO) is a pressure-driven membrane separation process using the tightest membranes available for liquid filtration. RO membranes primarily allow water molecules to permeate, while effectively rejecting dissolved and suspended substances such as salts, sugars, minerals, bacteria, spores, fats, proteins and gums. Only limited amounts of certain low-molecular-weight organic compounds may pass through.
RO is applied when maximum separation efficiency and high permeate purity are required. Reverse osmosis membranes are typically used for high-flux concentration of direct feed streams as well as permeates from ultrafiltration (UF) and nanofiltration (NF) processes.
Alfa Laval’s RO membranes are the only polypropylene (PP)-based RO spiral membranes available on the market, enabling enhanced tolerance to higher temperatures and wider pH ranges during cleaning-in-place (CIP) operations. Read more about our RO flat sheet membranes and RO spiral wound membranes
What is nanofiltration (NF)?
Nanofiltration (NF) is a membrane filtration process that allows small ions, such as minerals, to pass through the membrane while retaining larger ions and most organic components. Typical retained substances include bacteria, spores, fats, proteins, gums and sugars. This selective separation makes nanofiltration suitable for partial demineralization and concentration applications.
Alfa Laval nanofiltration membranes are widely used for high-yield concentration and partial demineralization of products such as whey and ultrafiltration permeate. These membranes are particularly effective at retaining large divalent salts while allowing smaller monovalent salts to pass into the permeate.
Nanofiltration is also applied in beverage processing, including the production of low-alcohol beverages, where alcohol passes through the membrane while colour, flavour and aroma compounds are retained in the retentate. Read more about our NF flat sheet membranes and NF spiral wound membranes
What is ultrafiltration (UF)?
Ultrafiltration (UF) is a pressure-driven membrane filtration process using membranes with a molecular weight cut-off (MWCO) of approximately 1,000 to 100,000 daltons. Low-molecular-weight components, such as salts, sugars, organic acids and small peptides, pass through the membrane as permeate, while higher-molecular-weight compounds, including proteins, fats and polysaccharides, are retained in the retentate.
By selecting membranes with appropriate MWCO characteristics, UF enables fractionation of a feed stream into distinct process streams enriched with different molecular weight components. This makes ultrafiltration a versatile technology for concentration, purification and fractionation in food, dairy and biotechnology applications.
Explore Alfa Laval's UF flat sheet membranes and UF spiral wound membranes for high chemical resistance and reliable performance in sensitive food-processing applications.
What is microfiltration (MF)?
Microfiltration (MF) is a membrane filtration process in which suspended solids, bacteria, and fat and oil globules are selectively retained—that is, they are the only substances prevented from passing through the membrane. This makes MF membranes ideal for removing small-diameter dispersed solids in applications where product composition must be preserved without altering the balance of components dissolved in the stream.
Alfa Laval microfiltration membranes are designed for cost-effective operation, largely as the result of the low energy consumption involved. They also have the advantage of eliminating the frequent replacement and disposal of the cartridges and other consumables used in traditional dead-end filtration.
Engineered for long-term performance, Alfa Laval microfiltration membranes offer exceptional mechanical and chemical durability, with service lifetimes that can exceed five years under normal operating conditions. Read about our MF flat sheet membranes and MF spiral wound membranes
Real cases of Alfa Laval membranes across industries
Discover how leading producers optimize performance and product quality using Alfa Laval membrane technology. See how different filter membrane types are applied in real-world processes to improve efficiency, reduce operating costs and ensure consistent results.
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Alfa Laval's Membrane and Application Development Test Centre
Alfa Laval has been a pioneer in membrane filtration since the mid-1960s, delivering complete, optimized systems that address every stage of the process. Our specialists collaborate with you to develop and fine-tune solutions that combine your process knowledge with our membrane filtration expertise at any stage of the process chain.
We design, manufacture and install membrane elements, modules and full filtration systems, providing reliable performance and complete support. Our facilities in Nakskov, Denmark, allow joint development and testing of solutions and serve as the core of innovation for our broad range of filter membrane types.
Membrane filtration technologies for industrial applications
Explore our comprehensive range of equipment, from membranes in multiple formats to auxiliary membrane components, test units, pilot plants and many more. Our membrane filtration equipment complies with global regulatory standards, including EU 1935/2004, 10/2011, 2023/2006, and FDA CFR Title 21, with USDA and Halal certification available upon request.
Membrane types
- Flat sheet membranes (RO/NF/UF/MF)
- Spiral membranes (RO/NF/UF/MF)
Pilot laboratory equipment
Industrial-scale systems
How can we help you?
We are one of the very few companies in the world that can scale its membrane filtration know-how seamlessly from R&D, testing and trials up to full-scale manufacture, and process implementation that you and your company can rely on completely.