Filtration is an important process used to purify water and other fluids. This process involves removing solid particles, making water fit for drinking. It uses a filter that captures solid particles. Interestingly, there are different types of filtration techniques. These types of filtration are based on how they remove particles.
These filtration types also vary in their efficiency and performance. However, one common thing is that all the filtration types use a filter medium. This medium acts as a barrier, ensuring that each particle is removed perfectly. In this article, I will discuss the most common types of filtration and how they work. So, let’s get started.
Types of Filtration Techniques
It is a misconception that filtration is only used to make water pure and drinkable. However, that’s not the truth. This technique is widely used across a wide range of industries. These include drinking water treatment, food & beverages, chemical industry, pharmaceutical, and more.
The use of filtration makes both fluids and gases pure and safe. As I said above, there are various types of filtration. Each type has its specific use in different industries and is used accordingly. In the section below, I will discuss types of these filtration techniques.
1- Mechanical or Straining Filtration
Mechanical or straining filtration is one of the most cost-effective techniques. In this method, a porous filter, such as sintered metal filters, is used. This filter medium has pores. The fluid is poured on it. Particles larger than the filter pores get trapped on the filter.
The liquid passes through this filter and gets cleaned. This filtration type is not ideal if the liquid contains microscopic (fine) dissolved particles. Why? The reason is that these particles are smaller in size than the pores. These particles will easily pass through the pores along with the fluid and don’t get removed. However, this technique is simple and does not involve any chemicals, which makes it stand out.
2- Pressure Filtration
This pressure filtration offers faster filtration and is highly efficient. It also uses a porous filter, and fluid flows through it. Instead of waiting for fluid to naturally flow through the filter, this process involves applying pressure. This force is applied to the feed (uncleaned or dirty fluid) to cause it to pass through the filter more quickly.
This way, all particles larger than the filter’s pores are trapped more quickly. Generally, a pneumatic system is used to deliver compressed air on the feed side. This compressed air applies pressure, ensuring fluid passes through the filter more quickly. You’ll see this filtration being used to remove contaminants from the slurries at industrial scale. It is worth noting that this method is very costly and complex due to the involvement of artificial pressure systems.
3- Gravity Filtration
As the name suggests, this filtration technique relies on gravity as its mechanism. Liquid is poured over filter media. However, no external pressure is applied to the fluid to force it through the filter. Instead, it’s gravity that pulls the fluid downward and passes it through the filter. This way, larger particles get trapped and removed.
This filtration method is typically slower, which makes it less efficient. This technique is also less suitable for removing fine particles from the fluid. However, it is very cost-effective and easy to use, which makes it stand out. In this filtration technique, sintered plastic filters are typically preferred. Why? The reason is that these filters are lightweight and easier to use than other types.
4- Hot Filtration
In some cases, the liquid gets different impurities. Some of these are soluble and get dissolved in the fluid, while others aren’t. In such a case, hot filtration is useful for removing insoluble impurities. In this method, the liquid is heated at a high temperature. This way, the solution impurities get dissolved in the fluid. However, the insoluble impurities and contaminants remain undissolved.
Then the heated liquid is poured on the filter medium. The liquid with dissolved impurities passes through the filter. However, the undissolved impurities get trapped on the filter and are removed. This method is slightly more complex as it requires dedicated heating systems. However, it is highly effective for removing impurities that don’t mix well with the liquid.
5- Cold Filtration
In hot filtration, insoluble impurities and contaminants are filtered out. However, soluble impurities get dissolved in the liquid and pass through the filter. So they are not removed, and that’s where cold filtration comes in handy. In this filtration, the liquid containing dissolved impurities is cooled to a low temperature.
This cooling causes the dissolved impurities to form solid crystals. The liquid then passes through the filter, and the crystals get trapped on the filter medium. This way, the crystal particles are removed, making the liquid purer. This filtration is used in laboratories where soluble contaminants must be removed.
6- Sand Filtration
Sand filtration is an effective method to remove dirt and other contaminants. In this method, a sand filter tank is used to remove contaminants. This tank consists of an outlet at the bottom. The dirty or contaminated water is poured into the sand-filled tank. This dirty water flows into the sand, where it is cleaned, and its contaminants, i.e., dust, are trapped in the grains of sand. Dirty water keeps going down, and its cleanliness keeps getting better. At the bottom, the water becomes very clean as its contaminants get trapped in the sand grains. From the bottom outlet, the pure or filtered liquid is taken out.
7- Vacuum Filtration
Vacuum filtration relies on creating a vacuum (low pressure) to draw the liquid. In this method, the filter medium is used. However, the vacuum pump is used to remove all the air from the container (funnel). Dirty liquid is poured over the filter.
The vacuum below the filter draws the water through it. This way, all solid particles, debris, and other particles are trapped and removed by the filter. This filtration method requires a dedicated vacuum pump. This makes this filtration method a bit more expensive. However, it is highly effective, accelerating contaminant filtration.
8- Surface Filtration
Surface filtration is similar to many other filtration techniques. In this method, the fluid passes through a filter, typically sintered bronze or stainless steel. Larger solid particles become trapped and remain on the filter surface. This buildup of the contaminant forms a filter cake on the surface of the filter paper.
The liquid, along with fine particles, passes through the filter. One thing that I don’t like about this filtration technique is the slow speed. The reason is that the filter cake clogs the filter, and the passage of liquid through becomes very difficult. You might have to remove these contaminants during filtration so that all the fluid can pass through it.
9- Depth Filtration
Depth filtration is another important type that involves the cleaning of contaminated or dirty liquid. This filtration technique is the opposite of surface filtration. In surface filtration, contaminants are trapped and accumulate on the filter surface. However, in depth filtration, the contaminants go deeper inside the filters. However, they remain inside the filters and don’t pass through.
Typically, the larger particles or contaminants are trapped on the upper surface of filters. However, smaller particles (fine ones) enter the filter and get trapped. So particles both larger and smaller don’t pass through the filter along with liquid. One thing is that particles are trapped inside the filters. So cleaning these filters becomes very difficult. You may not be able to use the filter more than once because it is difficult to clean.
10- Centrifugal Filtration
Centrifugal filtration involves spinning and rotating the liquid containing contaminants or solid particles. In this method, a container is rotated with controlled centrifugal force. Due to rotation or spinning, solid particles in the liquid rise to the surface. All the heavier particles move upwards while smaller particles remain inside the solution.
These heavier particles are then removed from the liquid, ensuring smooth filtration. Interestingly, this method can easily remove solid particles even when the liquid is present in large quantities. This filtration technique uses both pressure and gravitational force. As for drawbacks, the centrifuges used in this filtration process are expensive.
11- Membrane Filtration
In this filtration technique, a semi-permeable membrane is used. This technique is widely used because it can remove even very fine particles and microorganisms, i.e., bacteria. The liquid containing impurities or contaminants is passed through these semi-permeable membranes. This membrane has small pores that only allow liquid to pass through. Interestingly, the pores present on these filters are very small and thin.
As a result, even small particles and microorganisms become trapped on this membrane and cannot pass through its small pores. That’s how this filtration technique works. There are different types of material used in making these semi-permeable membranes. These include polysulfone, polyamide, polypropylene, and so on. This filtration type has further subtypes, e.g., microfiltration, ultrafiltration, and nanofiltration.
12- Activated Carbon Filtration
Is your liquid giving a bad odor, taste, or any chemicals mixed in it? If so, you should use activated carbon filtration to filter the liquid and make it clean. In this filtration technique, the activated carbon itself serves as the filter medium. The liquid is passed through this filter medium. The activated carbon captures the chemicals, chlorine, and impurities through adsorption. In fact, this method also removes the fluid’s bad odor. The contaminants or impurities stick to the surface of the activated carbon and are then removed. The liquid that passes through the activated carbon filter becomes pure and free of adsorbates.
13- Crossflow Filtration
As you know, when a filter is used to clean more liquid, it gets clogged by trapping solid particles. Clogged filters are less efficient and take longer to complete the filtration process. That’s where this crossflow filtration becomes very useful. In this filtration technique, the dirty liquid moves in parallel or across the filter.
The semi-permeable membrane is used as a filter in this method. Liquid (permeate) passes through this semi-permeable membrane. However, the contaminants remain trapped on the filter. Since the liquid keeps moving across the filter, the contaminants do not build up at one place to clog the filter. Instead, the contaminants are dispersed, ensuring the liquid flows smoothly through the filter.
Conclusion
In conclusion, filtration is an important process that helps purify different liquids and gases. Interestingly, this method is highly cost-effective, which is a significant advantage. However, different types of filtration processes differ in their basic principles and operation.
These filtration techniques also use filter media to remove solid particles from fluids. In this article, I have discussed the 13 most common filtration techniques. These methods are ideal for different use cases, and each has its own pros and cons. You should analyze the type of fluid you’re filtering and choose the appropriate technique.