Types of Water Filter Membranes

Filters can help remove odor, microorganisms, poor taste, chemicals and more from water. They are used in many different industries including water treatment, food and beverage manufacturing and mining.

They also can eliminate chlorine, which can cause neorological and respiratory harm. They can reduce the amount of Lead and Cryptosporidium that is found in drinking water.

Hydrophilic

Hydrophilic filters can be used with a wide variety of liquids including water and compatible non-aqueous fluids. They are also a good choice for biological applications where a filter that is resistant to protein binding can help prevent sample loss or adsorption to the membrane surface. These filters are often treated with a surface chemical to make them more soluble in polar liquids, making it easier for the fluid to wet the membrane evenly and minimize air bubble formation.

The term hydrophilic means “water loving” and is used to describe a substance that is attracted to or dissolves in water or other polar molecules. Essentially, hydrophilic substances are polar and can form hydrogen bonds with water molecules. When a droplet of water contacts a hydrophilic material, it spreads out uniformly, similar to how a drop of rain behaves on a freshly waxed car.

Most aqueous membranes are hydrophilic, but some are not. Strong acidic or alkaline solutions can cause these materials to swell, which could decrease the pore size and affect the performance of the membrane. This is why it is important to test a membrane for compatibility with these solvents before using it in a filtration application. A swelled membrane can also release extractables, which could be a concern for certain applications with heightened purity requirements.

Hydrophobic

Hydrophobic materials repel water and other polar liquids. They’re commonly used in medical and pharmaceutical applications, as they’re more able to prevent air bubbles from forming during the filtration process. In addition, they’re a great choice for separating chemically acidic or alkaline samples because they aren’t prone to damaging the membrane.

The term hydrophobic is derived from the Greek words for “water fearing,” or “fearful of water.” It describes the physical property of substances that are naturally resistant to wetting, as opposed to hydrophilic, which means “loving” (philic) water. Hydrophobic molecules tend to clump together when they come into contact with water, creating aqueous filter large surface areas and an extreme contact angle (approximately 180 degrees). This allows the liquid to roll away from the hydrophobic material, much like a magnet pushes metal objects away.

While this may seem counterintuitive, there are scientific reasons behind the hydrophobic effect. Hydrogen bonding is disrupted by the presence of nonpolar molecules, and the Gibbs free energy of the water phase rises significantly. This is compensated by van der Waals forces and the formation of weak hydrogen bonds at a hydrophobic surface.

As a result, the water molecules at a hydrophobic surface possess lower hydrogen-bonding energies and less entropy than in bulk water. This gives them water-steel filter a high dynamic range, which is why they’re so good at stabilizing biological proteins and other aggregations.

Pore Size

Pore size is a key parameter in determining the selectivity of membranes for water filtration. Narrow pore sizes usually offer high selectivity. Membrane manufacturers typically provide particle size retained data traceable to standards from the National Institute of Standards and Testing. However, the data may vary significantly from membrane to membrane due to polymer chemistry and other factors.

The pore size of an aqueous filter depends on the size of the particles that need to be removed. Syringe filters are available in a variety of pore sizes, so you can choose the one that suits your needs. For example, if you need to remove viruses from your water, choose a syringe filter with a pore size of 0.02 microns or smaller.

While pore size ratings are useful for selecting a membrane, they should be used in conjunction with other factors to ensure the proper performance of a specific application. To test the pore size of a membrane, immerse it in a sample of distilled water for hydrophilic membranes or alcohol for hydrophobic membranes. Then, slowly increase the gas pressure until a single bubble appears on the surface of the membrane. Record the gas pressure at this point to determine the pore size of the membrane. The bubble point test is a practical, nondestructive integrity test for sterilizing membrane filters and filter systems.

NSF Certification

The NSF Certification is a symbol that shows that a water filter has passed certain criteria and meets the claims made by the manufacturer. It is a seal of approval from the National Sanitation Foundation International, which has been in business since 1944 and is a not-for-profit organization that develops standards and inspects, tests, and certifies products that impact our health, safety and environment.

The process of achieving NSF Certification is thorough and comprehensive. It involves a number of steps that include submitting detailed information about the product, performing lab testing, and visiting the manufacturing facility to ensure that it is produced in a safe, sanitary manner. NSF also conducts unannounced annual inspections to make sure that the manufacturer maintains compliance with their NSF standards and protocols.

For example, Black Berkey filters meet NSF 42 standards for shower filters, which focus on aesthetic factors such as chlorine reduction and particulate reduction to improve water taste, odor, and clarity. Cloud RO water filters are pending NSF 58 certification, which is more stringent and focuses on the removal of lead, cysts, bacteria, and other harmful pathogens.

When looking at water filtration options, it’s important to know what NSF means and how it is different from other certifications, such as the EPA’s P231 protocol. The NSF Protocol is more stringent, requiring that water filtration systems are tested for actual pathogen reduction in worst-case scenarios.