Filtration: Definition, Types, Process, and Examples
Table of Contents
Filtration is the process where fluid is segregated from another substance in other form, such as solid with the help of the pores in a medium used for separation. The medium is the filter which can be physical, chemical and biological. In the liquids gases are also present.
Filtration is necessary to separate the wanted from the unwanted component, thus it plays a role in maintain homeostasis. The retention ability of kidneys in water and inorganic ion is an example of filtration.
It is a biological process where a mixture of sample is allowed to pass through a filter medium with a particular size pores, so that the required fluid can move through it whereas, the larger size suspended particles will get trapped on the membrane, however smaller size particle as that of the pore size can move with the liquid.
Thus, this is a biological technique to separate solids from liquids, which have been mixed together. The solution which has to be filtered, containing liquids and solids is known as slurry. Filter is a porous medium on which the solid will gather called the filter cake. The solution filtered is known as the filtrate.
Examples of filtration are removal of small suspended particles from AC’s air is one example and another example is while making tea and when pouring it in a cup separation of tea from tea-leaves using a sieve. Thus, various components of filtration are the filtration device, slurry, forces carrying out filtration and filter medium.
Components of Filtration Process
i. Filter Medium
Such a filter is supposed to be ideal which is not bothered by the substance found in the slurry, fluid flow resistance should be low and the filter has to be tensile. Filters can be made from materials like glass, cotton, rayon, nylon, wool and others.
Filters will differ from each other in texture, appearance, however, the weaving of material will determine its strength. Solid spherical beads made from supporting materials are also used for filtration.
Example are kieselguhr, pulp, sand, gravel and asbestos are some of the examples. Metal sheets are also used as filters.
As the solid size will vary from filtration to filtration, thus solid beds can also be used so that fluids can pass through it and solid will percolate on the solid bed. Materials like porous plastic, sintered glass, earthenware and metal can be used as filters. Filter selection will depend on the process, slurry and its composition.
The characteristics of slurry is having impact on filtration and thus, the characteristics are:
Solid’s property such as its size, density, firmness, compressibility and others.
Liquid’s property such as its consistency, weight, thickness and corrosiveness.
The amount of solid in the slurry. The main criteria of filtration is to segregate solids and liquids and various factors impact it such as filtration rate, process, method and others.
iii. Filtration Driving Force
The filtration rate is proportional to the difference of pressure to the filter cake and the medium, where difference in pressure can be obtained through routes such as:
Gravity: pressure difference can be achieved by positioning the slurry on top of the filter, where the difference in pressure will be achieved due to the gravity pull by liquid. The weight of the slurry will play a role in creating pressure difference and thus, gravity is dependent on it.
Low pressure: This can be done using a vacuum, where the low pressure is maintained by atmospheric pressure which is below the filter medium, thus creating a pressure difference, which should not be above 1 bar. Due to reduction in pressure, liquids boiling point is also reduced, thus, they may start to boil in the receiver. Although this is a major limitation, but is safer as well.
High pressure: Applying force on the slurry is also a mechanism for filtration which is used abundantly. Pressure difference is more seen in this than the reduced pressure.
Centrifugal force: The driving force for filtration process is provided by centrifugal force. Centrifugation is the movement of an object from the center point through a constant distance is known as Centrifugation. For the filtration to occur, difference in pressure is to be created.
Filtration can be seen in various processes such as physical, chemical and biological. The day-to-day activities we carry out such as filtering water at home, filtering tea, coffee, automotive and belt filters are some example.
In biology, filtration is done to remove microorganism from products. Another example is kidney filtration which removes toxins and waste through urination with the help of glomerulus filtration and keeps the necessary ions and water.
a) Gravity filtration: It is the most common type of filtration where; gravitational force is the driving force which carries out the filtration. In this technique, the funnel is clamped to the tripod stand containing filter and beneath is the conical flask, in which due to the gravitational force, liquid moves down, when poured over the funnel. Thus, the filtrate gets accumulated in the conical flask and the solid gets percolated on the filter forming a cake.
b) Vacuum filtration: In this filtration method, the driving force is vacuum. Although this technique is completely similar to the gravity filtration, but due to the use of vacuum, the filtration rate becomes quick. The setup comprises of Buchner flask on which funnel is placed containing filter. To the flask is vacuum connected, thus causing the movement of liquid from the funnel to the flask.
c) Centrifugal filtration: The driving force in this is the centrifugal force, which is the force exhibited by an object when rotating in speed, thus moving away from center in circular motion. In the rotating drum, slurry passes through it, where the filtrate is left on the drum’s wall and the liquid is released out of the drum due to centrifugal force.
d) Hot filtration: This method is used for liquids which forms crystals very quick and these crystal choke the filtration route. Thus, to prevent this from happening, temperature is raised so that filtration can occur. The filter paper used are fluted filter paper along with stemless funnel. The set up consist of a stemless funnel clamped to tripod on which is the filter and beneath is the Erlenmeyer flask, which is placed on hot plate, which takes out insoluble impurities.
e) Cold filtration: In this process, crystal formation is required and is the reverse of hot filtration. This process is used in the beer industry and here temperature is lowered, thus resulting in crystal formation, which separates the liquid.
f) Multilayer filtration: This type of filtration is seen, when filtering water from a fraction of layers such as sand, charcoal, active carbon, gravel, alum and others to get rid of impurities. In such a filtration, liquid passes through various layers and impurities are removed out at each step depending on the impurity size and the efficiency and efficacy as well increases, resulting in purified water.
Examples of Filtration
To get rid of impurities from water various treatments are employed to remove them and depending on the function of water, treatment is employed. Water required for drinking are treated through ceramic filters, activated carbon filters, depth filters, alloy filters, resin filters and micro and ultra-filtration.
To remove pollutants, microorganism and anything toxic from air, HEPA filters are used, where there are filters containing pores. These filters possess UV light and antimicrobial panels which remove all the impurities and filter out the air and have an efficacy of 99.9% and are found in vacuum as well.
There are automotive filters which remove particles from the air and fuel, thus increasing the shell-life and various filters are fuel filter, oil filter, cabin filter and air filter.
Aquariums also possess filters, but o 3 types chemical, biological and mechanical. On the basis of size, mechanical filters removes impurities like foam, sponges, gravel and others. The transformation of harmful nitrogen compounds to harmless compounds is done by biological filters. The absorption of chemicals liberated in water is done by chemical filters. Thus, these 3 types of filter maintain the balance and help in getting rid of impurities.
Another biological filter is the kidneys which remove toxins through the glomerular filtration and expels it through urine, but has retention property to store the required nutrients, however when kidney is unable is to carry out this process, due to improper functioning it results in accumulation of such toxins which can be fatal, thus dialysis is a process which eliminates all the toxins and unwanted waste from the body, thus behaving as artificial kidneys.
Belt filters in wine industry, mining, apple cider vinegar.
There are filters for gases as well, but different one. Like for oxygen and carbon dioxide there are different filters. For example, air contains various gases, thus there will be two filters which liberate purified oxygen and simultaneously there will be other filters for other gases like carbon dioxide.
Tea and coffee filters.
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