Key Difference – Filtration vs Centrifugation
Before moving on to an in-depth analysis of the difference between Filtration and Centrifugation, the two separation techniques, let us first see what a separation technique is. In biological science and engineering, a separation technique is used to isolate the desired constituent from a mixture. This is a mass transfer phenomenon that converts a mixture of constituents into two or more distinct fractions. Separation of mixtures depends on differences in chemical properties or physical properties such as mass, density, size, shape, or chemical affinity, among the constituents of a mixture. Separation techniques are often categorized according to the specific differences they use to achieve separation. Filtration and centrifugation are the commonly used separation techniques based only on the physical movement of desired particles. The key difference between filtration and centrifugation is in the utilized force and method. Filtration often uses a sieving technique to strain/remove out contaminants or undesired materials with the help of gravity. This can be achieved through physical barriers such as media, membranes, or strainers. Centrifugation utilizes the centrifugal force to separate the desired compounds and particulate based on the molecular weight. Centrifuge machine is used for this separation. The denser compounds transfer to the outside of the centrifuge and can be removed from there. In this article, let’s elaborate on the differences between filtration and centrifugation.
What is Filtration?
Filtration is used to separate desired particles or constituents in a mixture or suspension. Depending on the application, either one or more interested components can be isolated using filtration technique. It is a physical separation method and it is very important in chemistry, food science, and engineering to separate materials of different chemical composition or to purify compounds. During filtration, separation occurs at a single or multiple perforated layer/s. In filtering, particles that are too large to pass through the holes of the perforated layer are retained. Then, large particles may form a residue or cake layer on top of the filter and may also block the filter mesh, preventing the fluid phase from crossing the filter.
What is Centrifugation?
Centrifugation is a process by which a centrifuge machine is used to separate desired constituents of a complex liquid mixture/slurry. As a result of centrifugation, the precipitate is more rapidly and completely gathered on the bottom of the centrifuge tube. The remaining liquid is known as the supernatant liquid. This supernatant is then either rapidly transferred from the tube without disturbing the precipitate, or removed using a Pasteur pipette. The particles precipitating in centrifugation depend on centrifugal acceleration, particles’ size and shape, the volume portion of solids present, the density difference between the particle and the fluid, and the viscosity.
What is the difference between Filtration and Centrifugation?
Definition of Filtration and Centrifugation
Filtration: the act or process of removing something unwanted from a liquid.
Centrifugation: the process of separating lighter portions of a solution or a mixture.
Characteristics of Filtration and Centrifugation
Filtration and centrifugation may have significantly different characteristics and they can be categorized into following subgroups;
Filtration: The gravitational force is used in filtration.
Centrifugation: The centrifugal force is used in centrifugation.
Filtration: Sieves or perforated layer or strainer or media or physical membrane or filter funnel or their combinations can be used. Some filter aids can be used to help filtration. These are commonly incompressible diatomaceous earth or silica.
Centrifugation: Centrifuge machine and centrifuge tubes are used.
Method of Operation
Filtration: Large particles in the mixture cannot pass through the mesh/perforated structure of the filter while fluid and small particles pass under the force of gravity becoming filtrate (Figure 1)
Centrifugation: The solution mixture is centrifuged to force the heavier/denser solid to the bottom, where it frequently creates a firm cake The liquid above this cake can be removed or decanted. This method is particularly useful for separating solids which do not filter well (Eg: gelatinous or fine particles). (Figure 2)
Filtration: There are three filtration techniques based on the anticipated outcome known as hot, cold and vacuum filtration. Hot filtration technique is primarily used to separate solids from a hot solution. This is used in order to avoid crystal development in the filter funnel that comes in contact with the solution. Cold filtration technique is primarily used to rapidly cool the solution to be crystallized. This method results in the development of very small crystals as oppose to getting big crystals by cooling the solution slowly to a room temperature. Vacuum filtration method is primarily used for a small batch of the solution to quickly dry out small crystals. This is the most efficient filtration technique compared to hot and cool filtration.
Centrifugation: There are three centrifugation techniques namely micro-centrifuges, high-speed centrifuges, and ultra-centrifugations. Microcentrifuge is often used in research activities to process small volumes of biological molecules. This machine is small enough to fix on a table-top. High-speed centrifuges can handle larger sample volumes and are mainly used in large scale industry applications. Ultra-centrifugation is mainly used for research purposes such as studying properties of biological particles. It is the most efficient separation method compared to micro-centrifuges and high-speed centrifuges.
Filtration: Main purpose of filtration is getting the desired outcome by removing impurities from a mixture or, for the isolation of solids from a mixture.
Centrifugation: Main purpose of centrifugation is the isolation of solids from a solution.
Filtration: Simple filtration techniques may need a lot of time to separate desired material and as a result, filtration is less efficient than centrifugation.
Centrifugation: Separation occurs very quickly compared to filtration techniques. Therefore, centrifugation is more efficient than filtration.
Filtration: If very small amounts of solution are filtered, most of this solution may be absorbed by the filter medium. Mixtures containing gelatinous or fine particles do not filter well. Therefore, to separate these mixtures centrifugation can be used.
Centrifugation: This method requires know-how and electricity compared to filtration techniques.
Filtration: Cost depends on the complexity of the filtration process, and usually simple filtration techniques do not require electricity as well as trained persons. Therefore, the associated cost may be low compared to centrifugation.
Centrifugation: Cost is high compared to simple filtration technique because centrifuge needs electricity as well as trained technicians.
Filtration: Coffee filter, water filter, furnaces filter to remove particles, Pneumatic conveying systems use filters, in the laboratory, a glass funnel, a Buchner funnel or sintered glass funnel is used for filtration. In the human kidney, renal filtration is used to filter blood and selective re-absorption of many elements vital for the body to maintain homeostasis.
Centrifugation: One of the most common applications is the treatment of sewage sludge where the separation of solid from highly concentrated suspensions. Centrifugation is also used for uranium enrichment process. In addition to that, this technique is used in biological research for isolation of desired solid or liquid from a mixture. In addition, centrifugation is used to remove fat from milk to produce skimmed milk, to clarify and stabilize the wine and to separate of urine constituents and blood elements in forensic and medical research laboratories.
In conclusion, filtration and centrifugation are different separation techniques and the key difference between them is the utilized force and separation equipment. As a result, they may have substantially different applications.References: Harrison, Roger G., Todd, Paul, Rudge, Scott R. and Petrides D.P. Bioseparations Science and Engineering. Oxford University Press, 2003. Cao, W. and Demeler B. (2008). Modeling Analytical Ultracentrifugation Experiments with an Adaptive Space-Time Finite Element Solution for Multicomponent Reacting Systems. Biophysical Journal, (95), 54–65.