Furthermore, the force that moves the fluid through the filter—whether gravity, a vacuum, or pressure—is another defining factor. The type of filter used can also serve to distinguish varieties of filtration.
In liquid filtration, such as that applied in sewage treatment, a liquid can be pulled through the filter by gravitational force, as in the examples given. On the other hand, some sort of applied pressure, or a pressure differential created by the existence of a vacuum, can force the liquid through the filter. Water filtration for purification purposes is often performed by means of gravitation. Usually, water is allowed to run down through a thick layer of granular material such as sand, gravel, or charcoal, which removes impurities.
These layers may be several feet thick, in which case the filter is known as a deep-bed filter. Water purification plants may include fine particles of charcoal, known as activated carbon, in the deep-bed filter to absorb unpleasant-smelling gases. For separating smaller volumes of solution, a positive-pressure system—one that uses external pressure to push the liquid through the filter—may be used. Fluid may be introduced under pressure at one end of a horizontal tank, then forced through a series of vertical plates covered with thick filtering cloths that collect solids.
In a vacuum filter, a vacuum an area virtually devoid of matter, including air is created beneath the solution to be filtered, and as a result, atmospheric pressure pushes the liquid through the filter.
When the liquid is virtually freed of impurities, it may be passed through a second variety of filter, known as a clarifying filter. This type of filter is constructed of extremely fine-mesh wires or fibers designed to remove the smallest particles suspended in the liquid. Clarifying filters may also use diatomaceous earth, a finely powdered material produced from the decay of marine organisms. Gas filtration is used in a common appliance, the vacuum cleaner, which passes a stream of dust-filled air through a filtering bag inside the machine.
The bag traps solid particles, while allowing clean air to pass back out into the room. This is essentially the same principle applied in air filters and even air conditioning and heating systems, which, in addition to regulating temperature, also remove dust, pollen, and other impurities from the air. Various industries use gas filtration, not only to purify the products released into the atmosphere, but also to filter the air in the workplace, as for instance in a factory room where fine airborne particles are a hazard of production.
The gases from power plants that burn coal and oil are often purified by passing them through filtering systems that collect particles. Sewage treatment is a complex, multistage process whereby waste water is freed of harmful contents and rendered safe, so that it can be returned to the environment. This is a critical part of modern life, because when people congregate in cities, they generate huge amounts of wastes that contain disease-causing bacteria, viruses, and other microorganisms.
Lack of proper waste management in ancient and medieval times led to devastating plagues in cities such as Athens, Rome, and Constantinople. Indeed, one of the factors contributing to the end of the Athenian golden age of the fifth century B.
The horrors created by improper waste management reached their apogee in , when microorganisms carried by rats brought about the Black Death, in which Europe's population was reduced by one-third. Small amounts of sewage can be dealt with through aerobic oxygen-consuming decay, in which microorganisms such as bacteria and fungi process the toxins in human waste. With larger amounts of waste, however, oxygen is depleted and the decay mechanism must be anaerobic, or carried out in the absence of oxygen.
For people who are not connected to a municipal sewage system, and therefore must rely on a septic tank for waste disposal, waste products pass through a tank in which they are subjected to anaerobic decay by varieties of microorganisms that do not require oxygen to survive.
From there, the waste goes through the drain field, a network of pipes that allow the water to seep into a deep-bed filter. In the drain field, the waste is subjected to aerobic decay by oxygen-dependant microorganisms before it either filters through the drain pipes into the ground, or is evaporated. Municipal waste treatment is a much more involved process, and will only be described in the most general terms here.
Essentially, large-scale sewage treatment requires the separation of larger particles first, followed by the separation of smaller particles, as the process continues. Along the way, the sewage is chemically treated as well.
The separation of smaller solid particles is aided by aluminum sulfate, which causes these particles to settle to the bottom more rapidly. Through continual processing by filtration, water is eventually clarified of biosolids that is, feces , but it is still far from being safe. At that point, all the removed biosolids are dried and incinerated; or they may be subjected to additional processes to create fertilizer. It is the most common method of separation that we come across in our daily life.
From a morning tea or coffee to a relaxing shower before bed, we come across several filtration processes during our daily routine. Paper, fabric, cotton-wool, asbestos, slag- or glass-wool, unglazed earthenware, sand, or other porous material can act as a filter. Technically, the size of the porous membrane should be smaller for any material to serve as a filter than the impurities that are to be removed. Depending on the size of the impurities or the required filtrate, one can determine the size of the suitable filter.
However, one should not confuse filtration with sieving, where separation occurs at a single perforated layer a sieve. To be more specific, a sieve sets a threshold calibration through which all undersized materials, being in the same phase with others, can pass through, whereas a filter isolates materials based on their qualities such as size, phase, reactivity, and polarity.
Due to such properties, filtration is very commonly used and makes our life easier on daily basis. Coffee is one of the most loved beverages around the world. It is an infusion of ground or roasted coffee beans that are admired for their taste and aroma.
Also, its caffeine content plays an important role in its popularity. When people think of coffee, they usually think of its ability to provide an energy boost. However, studies have shown that coffee can have various side effects on human health. Therefore, it is advised to drink filtered coffee. A coffee filter is a coffee-brewing equipment, usually made of disposable paper. It helps to trap the coffee grounds and allows the liquid coffee to flow through this equipment.
Compared with unfiltered coffee, filtered coffee is associated with a lower risk of dying from cardiovascular disease, ischemic heart disease, or stroke.
Unfiltered coffee contains substances that increase blood cholesterol. With the help of a filter, we get filtered coffee that reduces the chances of heart problems and premature death. Moreover, drinking filtered coffee through a paper filter is found to be healthier than drinking no coffee at all. The relaxing, invigorating, and mood-altering qualities of tea have been familiar to the world for centuries.
Tea has been an intricate part of our daily routine, and therefore, to keep up with the pace of modernization, several advancements have been made to its preparation methods.
The device initially used for the separation of dried tea-leaves from the liquid tea was tea-infuser, which has now been replaced by the handy tea-bags. A tea bag is a small, porous, sealed bag or packet, typically containing tea leaves, that acts as a filter when immersed in water to allow tea leaves to make an infusion. Originally used only for tea Camellia sinensis , tea bags now contains several other varieties of herbal tea-leaves as well.
With the growing population, industrial development, and environmental pollution, pure and safe drinking water is not easily available these days. Although water is known to be a self-purifier, there are still some impurities that can not be removed by natural processes. Thanks to the technology that we have several types of water filters attached to our water supply systems.
A water filter removes impurities by lowering contamination of water using a fine physical barrier, a chemical process, or a biological process. Filters cleanse water to different extents depending on several purposes such as providing agricultural irrigation, accessible drinking water, public and private aquariums, and the safe use of ponds and swimming pools.
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 salt water, which can be done easily by means of filtration process using a Whatman filter paper of Grade 1. The sand remains on the filter paper is called as residue, whereas salt water now called the filtrate passes through the filter paper and is collected in a beaker.
Another good example is filtration of air from dust in an air conditioner. Here, pure air is sucked inside by the air conditioner contains dust. These dusts are 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. Few examples are:.
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 residue. Nowadays vacuum cleaners are used with attached filters to soak the dust inside. In rainwater harvesting, the rain water 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 organism like insects are filtered out to get clean water. 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. Many oils are made scented and full of nutrients by absorbing the essential oils of other flowers, fruits and nuts.
They are then filtered and used as medicinal remedy. In laboratories, filtration is a very important process.
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