Membrane
Filtration

In short, membrane filtration methods employ one or more membranes for the filtration process. A membrane is a thin layer of a material that provides a physical barrier to separate molecules and particles of various sizes and characteristics. Even the smallest elements, such as bacteria and viruses, can be rejected by membranes. A membrane can be made of several organic and inorganic materials and constructed in various module designs.

This enables the membrane to filter different types of liquids or gases. Membrane filtration is a pressure-driven technology. No chemicals are added to treat the water and gases. Chemicals are only needed for membrane cleaning to maintain superior hygiene. Thus, it is a clean technology, securing a greener future.

Membranes can either be produced from organic or inorganic materials. Organic membranes are polymer membranes and are mainly used for liquid filtration. A polymer membrane is a semi-permeable filter media made of polymeric materials such as polysulfone, polycarbonate, polyvinylidene fluoride, polyamide, or cellulose acetate. Dive more into polymer membranes here.

An alternative to polymer membranes is ceramic membranes, which can be produced from various inorganic materials. One of the materials is the solid, long-lasting material silicon carbide (SiC). SiC is the second hardest material in the world, and SiC membranes are rapidly emerging as it provides some unique advantages compared to traditional ceramic and polymeric membranes. This is the membrane LiqTech is specialized in. Dive into the details about silicon carbide membranes here.

Simply put, a pressure pump applies pressure to force the feed stream through the membrane. This will separate the feed stream into two streams: the permeate and the retentate. The permeate consists of the substances that can pass through the membrane surface. It is either liquid or gases the membranes filter. The retentate consists of rejected particles, which are held back by the membrane surface.

The membrane’s pore size structure defines the size of the particles that are retained. Membranes can be made with various pore sizes. The smaller the pore size, the smaller particles can be retained. This enables filtration processes of different types of liquids and gases. A membrane’s pore size is measured in microns. One micron is equal to one millionth of a meter. This extremely fine measurement is crucial for pore size structures to establish what kinds of particles a membrane can reject. While human hair is approximately 50 microns, bacteria can be as small as 1-10 microns. Thus, micron rating is essential to define what kinds of particles a filter can retain. This also determines for which filtration applications and industries a membrane is useful.

Various industries use membrane filtration methods. Membrane filter techniques are essential in large-scale industrial applications to treat liquids and gases.

Within water treatment, water filter membranes are critical technology behind many water treatment systems. Water filter membranes can be used to treat drinking water and pool and spa environments to control and prevent diseases by removing bacteria, viruses, and pathogens. It can also be used within the food and beverage industry to purify and concentrate liquids. Still, membrane filtration is also employed within arduous industries with aggressive fluids, such as oil and gas, power plants, and marine to remove polycyclic aromatic hydrocarbons (PAH), particulate matter (PM), pathogens, and heavy metals from wastewater. Membranes can comply with even the strictest wastewater discharge limits.

Furthermore, liquid filtration can be used to extract liquid substances, such as acid purification. This means that within wastewater treatment, it is the permeate, which is clean water, which is the product, whereas, within acid filtration, it is the retentate, which is the wanted product.

Within gas treatment, membrane filtration is the lever to various emission technologies. It can be used for diesel particulate filters (DPF) and autocatalysts, ideal for vehicles that produce high soot loads, such as garbage trucks, port vehicles, diesel pick-up trucks, intra-city vehicles, and off-road vehicles.

Membrane filtration provides reliability, consistent filtration results, and constant compliance. With more and more environmental regulations on wastewater treatment and emission reduction set by various national and international regulatory institutions to seek a greener future, reliable and consistent filtration solutions are imperative to obtain constant compliance. Compliance is essential to avoid operational downtime and heavy fines affecting your OPEX.

Moreover, membrane filtration reduces energy consumption compared to other filtration technologies, making it a cost-effective solution. Add to that, once you treat your wastewater, you can optimize your water management and take an active role in protecting scarce resources. Industrial wastewater can be reduced for other industrial processes, maintenance, or sold of irrigation. This ensures reduced OPEX.

There are many more advantages of membrane filtration. At LiqTech, we have more than 20 years of experience developing, producing, and marketing proprietary ceramic membranes for various large-scale industrial applications.

The LiqTech ceramic membranes are ideal for aggressive fluids. See its features and benefits here:

• pH 0 to 14
• Abrasion-resistant
• Temperature: up to 800 ˚C
• Robustness
• Low maintenance
• Long-term performance
• Unmatched performance

The four techniques are:

• Microfiltration
• Ultrafiltration
• Nanofiltration
• Reverse osmosis

In short, microfiltration is a filtration process to separate larger suspended solids and micron-sized particles. Microfiltration is an excellent range to use for pretreatment before other filtration applications within nanofiltration or reverse osmosis. 

Ultrafiltration is, like microfiltration, a pressure-driven membrane filtration technique used to treat various types of water and wastewater to remove suspended solids and solutes. UF can, among others, be used to remove bacteria, viruses, colloids, proteins, pyrogens, and pathogens. 

Nanofiltration is a filtration process used to separate low total dissolved solids and particles, such as inorganic salts and small organic molecules.

Reverse osmosis is the finest filtration technique, rejecting dissolves solids like salts and ions. RO is used in drinking water treatment.

The scheme below shows the different techniques’ rejection rates.