Different Types of Filtration Technology

Filtration technology involves many different processes and equipment to separate, concentrate and clarify liquids. It can be used in various applications depending on the industry’s needs.


Sediment filters offer physical filtration by reducing large suspended contaminants in water. They also protect later filter stages like adsorption and membrane filters, extending their lifespans.

Membrane filtration

Membrane filtration is a process that uses semi-permeable membranes to separate components of liquid solutions or gas mixtures. It allows for higher overall yields and fewer waste streams due to its ability to separate and concentrate materials. It also reduces costs by eliminating the need for residue disposal and resulting energy usage. This type of separation is commonly used in the food industry.

The membrane separates the liquid into two distinct streams using a pressure difference between the front and back of the membrane. This force causes the molecules in the liquid that are smaller than the membrane pores to flow through the membrane into the permeate stream, while retaining those that are larger than the pores as the retentate. The retentate is then separated from the liquid being filtered by the use of tangential flow that helps to crack the membrane filter cake and reduce fouling.

Because of its unique characteristics, membrane filtration has a high level of flexibility and can be used in many applications. However, it is important to understand the specific needs of the application before selecting a system. For example, different membranes have different pore sizes, which can affect the separation capabilities of the system. Additionally, membranes must be cleaned regularly to prevent irreversible fouling. This is often accomplished through a combination of back-flushing, pressure backpulsing, or chemical cleaning.

Sedimentation filtration

Sedimentation filtration separates solid particles from a liquid. It is often referred to as settling and is a regular process in water and wastewater treatment. Solids can include fine sand, silt and colloids.

Gravity is the dominant force in sedimentation. However, the settling process can be accelerated with a clarifying agent, which groups the smaller particles together so they fall out of suspension faster. Centrifuges can also speed up a settling process by spinning the liquid at high speeds to create a force many times greater than gravity, separating out even smaller particles.

A sediment filter traps dirt and other debris from the water through a mesh sieve-like screen with different sized holes. The holes are arranged so that larger particles will get caught on the outside of the screen, while the smaller ones will pass through and reach the bottom. This process can be seen in coffee percolators, tea bags and fish tank filters as well as in the filtration screens at sewage treatment plants.

The most common type of sediment filter is a spun-down filter that uses large surface areas to catch the bigger particles. Other types of sediment filters use a depth gradient that forces the water through layers of filter media. These filters force the water to flow through walls of sediment with increasing tightness, reducing the particle size and catching more particles as the water flows towards the core of the filter.

Carbon filtration

Activated carbon filters remove contaminants from water through the process of adsorption. The surface of activated carbon has numerous cracks and pores that can trap a variety of chemicals and contaminants, much like a magnet attracts iron filings. Activated carbon is commonly used to remove organic constituents from drinking water supplies, unwanted disinfection byproducts, and trihalomethanes (THMs). The removal of these compounds not only improves taste but also protects other treatment technologies such as reverse osmosis membranes and ion exchange resins from damage.

Unlike GAC (granular activated carbon) water filters, which are comprised of tiny granules, carbon block filters are densely packed blocks of activated carbon that contain multiple pores. Because of this, carbon block filters have a larger surface area than GAC, which allows them to capture more contaminants. Carbon block filters also have a longer contact time, which can improve their ability to remove VOCs such as solvents and pesticides.

Carbon water filters can be made from a variety of raw materials, including coal, nutshells, wood, and petroleum coke. They are generally heated to 1000 degrees Fahrenheit in the absence of oxygen to bake the material and “activate” it, a process that increases its pore structure and reactivity. Activated carbon can be further refined to produce different grades with unique properties, including hardness, pore size, and surface area.

Reverse Osmosis

Reverse Osmosis is a membrane-technology filtration method that reverses the natural process of osmosis to remove contaminants from water. The reverse osmosis system uses pressure to force water through a semi-permeable membrane with small pores that block contaminants but allow water molecules to pass through. This leaves a more concentrated solute on one side of the membrane and a pure solvent on the other side. This process is commonly used in water purification and desalination.

Reverse osmosis systems are often combined with sediment and carbon pre-filters to prevent contaminants from clogging the filter. They can also be used to remove chlorine, volatile organic compounds (VOCs), PFAS, arsenic, lead, and other heavy metals, as well as dissolved minerals and chemicals. Point-of-use systems are typically installed at a single fixture and can be connected to kitchen sinks or other faucets.

A typical Reverse Osmosis system consists of four stages: a sediment filter, pre-carbon filter, reverse osmosis membrane, and a post-carbon filter. The first stage filters out the largest particles, such as dirt and sand, to prevent them from clogging the reverse osmosis membrane. The next step filters out VOCs and PFAS to protect against potential health issues. The third step filters out the remaining chemical contaminants and minerals, including sodium, high levels of lead, dissolved minerals, and fluoride.

While reverse osmosis can remove many types of contaminants from drinking water, it does not always remove beneficial minerals like calcium and magnesium. These minerals are necessary for healthy bones and muscles. However, consuming too much of any mineral can be harmful, so it’s important to balance your diet with the proper amount of each mineral.