For the students of Chemistry, it is important to learn about the process of Filtration, but there is one thing that the students always have to keep in mind, which is that the explanation of the topic must be done in a language that is easy for the students to understand, otherwise instead of clearing the concept of filtration, the explanation only complicates it. Therefore, to make it easy for the students to understand, provides a complete explanation of the Filtration, along with its definition, process, and examples.
Understanding the Concept of Filtration
In liquid and gaseous fluids, the solid particles are always present, and the process which is used in order to remove such solid particles from the liquid and gaseous fluids is known as Filtration. What generally happens here, is that the medium which is used as a filter, allows the liquid fluid to pass through but retains the solid particles inside it, and hence the liquid fluid is filtered. An interesting fact about filtration is that the process of filtration is used not only for the liquid fluid, but it is also used for filtration of electricity, light, sound, but of course, the method is different.
The process of filtration has been known to humans for so many years now. Earlier humans used to dig a hole in the sand on the bank of the river, in such a manner that it has a depth below the level of the river water level, therefore the water enters into the hole and gets filtered by the sand. The modern process of filtration works on the same principle, but the only difference is that it works on a large scale with the use of sophisticated machinery.
While opening the bonnet of cars we must have observed that most of the people were cleaning the car air filter which had collected dust in its long run. In a similar way, in our room, we must have cleaned the filter attached in front of an air conditioner to remove the dust.
Filtration Definition
Filtration is a physical process by which the solid particles are separated from liquids or gases using a filter or a membrane as a medium that retains solid particles and let the liquid or gases pass through the membrane or filter.
What is Filtration?
Filtration Process: A filter or a membrane is used to separate substances in two different states and the process is called the filtration process. The physical states in which the substances can occur are solid and liquid or solid and gas. Here, generally, the filters are physical, biological, or mechanical in nature.
The fluid that is filtered out is called the filtrate and the solid that remains or is collected on the filter is the residue. The thin filter medium is a barrier that is crossed by very minute particles of liquid whereas big grains stay on the filter.
Filtration Diagram
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This kind of filtration is most common using gravity to settle the matter first. The mixture is then poured on a filter paper and through the gravitational pull, the water drips which is collected as filtrate, and the residue remains in the filter paper itself.
Filters in Use: Filtration Examples: Some of the most common filter aids used were silica, diatomaceous earth, cellulose, and perlite. They can be used alone or with paper filters.
A very simple and proven example of filtration is that if we have sand, salt, and water in a beaker, then the salt gets dissolved in water whereas sand remains as such and it settles down at the bottom of the beaker. Now, we need to separate sand from saltwater, which can be done easily by means of filtration process using a Whatman filter paper of Grade 1. The sand remaining on the filter paper is called a residue, whereas saltwater now called the filtrate passes through the filter paper and is collected in a beaker. Another good example is the filtration of the air from dust in an air conditioner. Here, pure air is sucked inside by the air conditioner containing dust. This dust is never seen through naked eyes. So, when a filter is attached in front of the AC the dust is collected on the filter and we receive pure air which is an example of filtration of solid in gas.
Applications of Filtration
In our daily life, we apply the process of filtration in many ways. A few examples are:
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We filter the hot tea using a mesh filter, where milk has dissolved the juices of tea leaves and sugar that is filtered out as filtrate whereas tea dust or leaves remains as a residue. We brew coffee powder in hot water after filtering the liquid coffee is the filtrate and the large particle or coffee dust remains as a residue.
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Nowadays vacuum cleaners are used with attached filters to soak the dust inside.
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In rainwater harvesting, the rainwater is stored in a tank. This water is passed through pumps into several sedimentary tanks and filters and then made disinfectant before using it for household purposes. In this way, the soil, sand, and other biological organisms like insects are filtered out to get clean water.
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In our kidneys, blood is constantly filtered through the microscopic filter, glomerulus, where the essential nutrients are absorbed back and urea is a toxic residue that is collected in the kidney and discharged out of the body.
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Many oils are scented and full of nutrients by absorbing the essential oils of other flowers, fruits, and nuts. They are then filtered and used as medicinal remedies.
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In laboratories, filtration is a very important process. Many oil-based substances are dissolved in oil and water-based substances that do not dissolve remain as residue that can be again dissolved in water and used.
Seven Steps of Water Purification Process
The detailed steps followed for water treatment depend solely on the nature of raw water and the required standard of water quality used in the industry and households. General steps used for purification of drinking water include:
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Aeration of Water: Raw water is collected in a large aeration tank. Air is passed through the water by means of perforated pipes. Aeration removes bad odors and [CO_{2}]. Some of the unwanted metals such as manganese, iron in the water can be removed by precipitating them as hydroxides.
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Storage or Settling of Dust and Wastes: Aerated water is kept in a settling tank for 10 to 15 days. By this process solids as well as heavier metals settle down at the bottom of the tank which makes the water clear. Pathogenic bacteria gradually die as well as some of the organic matter in the water gets oxidized during storage.
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Coagulation Tank: Water is then placed in the coagulation tank. Some precipitating agents, such as lime, alum, etc. are mixed in the water. These agents from Aluminium hydroxide, [Al(OH)_{3}] precipitate when it is mixed with water. Thus, suspended solids absorbed on the surface of the lime/alum particles are precipitated out of the water and settle down at the bottom of the tank.
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Filtration: Water is then passed through sand in a gravity filter. Here, about 98% of microorganisms and other impurities are eliminated.
Gravity water filter tank has the basic three layers:
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Top Layer: It is a fine layer of 1-m thickness.
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Middle Layer: It is a 0.3- to 0.5-m thick layer of coarse sand granules.
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Bottom Layer: It is a 0.3- to 0.5-m thick layer of white gravel.
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Collection Tank: At the bottom of the filter bed there is a collection tank that collects the filtered water.
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Disinfecting the Water: Disinfectants like chlorine kill pathogens as well as other microorganisms in water.
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Overhead Storage Tank: Disinfected water is pumped into this tank to keep water for domestic distribution.
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