Filtration is the mechanism by which suspended solid matter is removed from a liquid by allowing it to move through the porous material, called a filter. The term “filtration” applies whether the filter is mechanical, biological, or physical. The filtrate is called the liquid that has run through the filter. Perhaps, 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 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 with one quality from materials without that quality – size, phase, reactivity, polarity, etc. In chemical technology, filtration is very commonly used and makes our life easier on daily basis. Let’s discuss a few of its examples in everyday life:
1. Coffee Filter
Coffee is one of the most loved beverages around the world. It is an infusion of ground, roasted coffee beans, that is admired for its taste and aroma, its caffeine content possibly plays a 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 utensil, usually made of disposable paper. This enables it to trap the coffee grounds and allow the liquid coffee to flow through. Compared with unfiltered coffee, filtered coffee was associated with a lower risk of dying from cardiovascular disease, ischemic heart disease or stroke. Unfiltered coffee contains substances which increase blood cholesterol. Using a filter prevents these and makes it less likely to cause heart problems and premature death. Moreover, drinking filtered coffee through a paper filter, for example, was found to be healthier than drinking no coffee at all. In contrast to drinking no coffee, filtered coffee was related to a 15 % reduced risk of death from any cause, a 12 % reduced risk of death from cardiovascular disease in men and a 20 % reduced risk of death from heart disease in women.
The relaxing, invigorating, and mood-altering qualities of tea are familiar to the world for centuries. Apart from quenching thirst, the calming effects of the beverage produced from the leaves of the plant “Camellia sinensis” are known to help in meditation and soothing the nerves for better mental health. Nevertheless, preparing perfect tea is considered nothing less than art by tea lovers. 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, which is immersed in water to steep and make an infusion. Originally used only for tea (Camellia sinensis), they are now made with other varieties of herbal tea-leaves as well.
3. Water Filters
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 for purposes such as providing agricultural irrigation, accessible drinking water, public and private aquariums, and the safe use of ponds and swimming pools. For home use, water filters include granular-activated carbon filters (GAC) used for carbon filtering, depth filter, metallic alloy filters, microporous ceramic filters, carbon block resin (CBR), filters with microfiltration and ultrafiltration membranes. Some filters use more than one filtration method, e.g., a multi-barrier system. Some kettles have built-in filters, primarily to reduce limescale build-up.
4. Sand Filtration
Sand filtration is a process in which the treatment of the water is realised by the ‘porous’ nature of a sand layer which traps particles present in water. Wastewater management facilities around the world widely make use of this technology. Sand filters usually come in three major types: rapid (gravity) sand filters, upward flow sand filters and slow sand filters. While the first two include the use of flocculant chemicals to function effectively, slow sand filters may deliver very high-quality water with the removal of pathogens from 90 %to >99 % (depending on the strains), taste and odour, without the need for chemical aids. However, the main discrepancy between slow and fast sand filters is that the top layer of sand is biologically involved when microbial species are added to the slow sand filters. The filter depth is 0.9 to 1.5 meters recommended and widely used. In 10–20 days from the start of the process, a microbial layer is formed. After a certain period of time, the filter is saturated with particles and must be cleaned to prevent it from blocking up completely. Sand filters are cleaned by backwashing with air and/or water
5. HEPA Air Filters
HEPA stands for high-efficiency particulate air. A HEPA filter is a type of mechanical air filter that operates by pressing air through a fine mesh, which collects dangerous particles such as pollen, pet dander, dust mites and tobacco smoke. HEPA filters are essential in avoiding the transmission and, thus, contamination of bacterial and viral species in the air. In fact, high-energetic ultraviolet light systems or anti-microbial layer panels usually include HEPA filtering systems to eliminate live bacteria and viruses stuck on filter media. Some of the most highly trained HEPA systems have a 99.995 % performance rating, which ensures high standards of safety against transmission of airborne conditions. Using a HEPA filter in your home can remove most airborne particles that might make allergies worse. But the particles suspended in air are not the only ones in your home. There are far more in your rugs, bedding, and drapes, and resting on countertops and tabletops. Therefore, this technology is also employed in the manufacturing of vacuum cleaners. To work efficiently, the HEPA filter in a vacuum cleaner must be built to disperse all the air drawn into the machine from the filter without any air escaping behind.
6. Automotive Filters
Filters play an important role in extended the life of vehicles and protecting against premature wear and tear. Typically consisting of a fibrous mesh material, they prevent particulate matter to enter the vehicle and cause any damage. Most of the automotive vehicles mainly come with four types of filters: Air Filter, Fuel Filter, Cabin Filter, and Oil Filter. Understanding them all can get complicated, but it’s important to know what each one does to keep vehicles in tip-top shape.
- Air Filter: Just as humans need oxygen to breathe, a car needs oxygen for the combustion process. The air filter prevents any insects, dust, particles, sand or debris reaching the engine and ensures a good mixture of air and fuel to support performance. Car air filters come in different shape panels, circular or cylindrical.
- Cabin Filter: The cabin air filter is designed to filter the air which enters the cabin of your vehicle. When the cabin air is switched on, the air passes through the filter of the cabin before entering the vehicle. Failure to replace the cabin air filter of your vehicle could lead to decreased HVAC efficiency while also contributing to airborne pollution inside the vehicle.
- Fuel Filter: When fuel comes out of a refinery, it’s clean. Then, before it reaches the car, it goes into trucks and gas station tanks where it may get polluted. The fuel filter keeps the engine dirt, grime, and water out of it. The fuel filter is a cartridge located in the fuel line. Inside the cartridge, there’s a screen that catches dirt, rust, and other debris in the fuel before it passes through to the fuel injector.
- Oil Filter: Another common type of automotive filter is the oil filter. As you may know, the oil filter works to remove pollutants from the engine oil. As the oil travels from the drip pan to the engine, it passes through a filter where debris is removed. The good news is that most mechanics and auto shops will replace the oil filter when you get an oil change
Over time, however, filters may restrict the flow of air or liquid. As particulate matter accumulates on a filter, the filter may create a blockage that impedes the performance of your vehicle.
7. Belt Filters
The belt filter, sometimes called a belt press filter or belt filter press, is an industrial machine, used for solid/liquid separation processes, particularly the dewatering of sludges in the chemical industry, mining, and water treatment. The filtration process is primarily achieved by passing a pair of filtering cloths and belts through a roller system. A sludge or slurry is taken as a feed by the system and divided into a filtrate and a solid cake. The filter cloths are made from synthetic materials such as polypropylene or polyester with monofilament or multifilament yarns and with sophisticated weaves and layers. Belt filters are also used in the manufacturing of apple cider, vinegar, and in winemaking.
Healthy kidneys clean your blood and remove extra fluid in the form of urine. They also make substances that keep your body healthy. Dialysis replaces some of these functions when your kidneys no longer work due to some unfortunate reasons. Dialysis works on the principles of the diffusion of solutes and ultrafiltration of fluid across a semi-permeable membrane. A semipermeable membrane is a thin layer of material that contains holes of various sizes, or pores. Smaller solutes and fluid can pass through the membrane, but it blocks the passage of larger substances (for example, red blood cells and large proteins). Blood tubing carries your blood from your body to the dialyzer. Like the kidneys, the filters remove the waste products from the blood. The filtered blood then returns to the patient through another catheter. The whole system almost works like an artificial kidney.
9. RO Filters
If you live in an urban area, you may have heard of the RO devices that are used for the water purification process. The Reverse Osmosis filtration system works by pressing water through a semi-permeable membrane to eliminate impurities that may not be visible to the naked eye. Water goes through a combination of filters in RO purifiers, such as sediment, carbon filter, RO membrane, UV lamp, UF membrane, and post-carbon filter. All these elements have specific properties that help in removing specific kinds of impurities. A Reverse Osmosis membrane has small pores that block contaminants but allow water molecules to flow through. In osmosis, water from the less concentrated side, i.e. without impurities, will flow through a semipermeable membrane to the water with higher concentration, i.e with impurities. In Reverse osmosis, however, this flow is reversed by the application of external pressure. For example, when pressure is applied to a volume of saltwater during reverse osmosis, the salt is left behind and only clean water flows through. The membrane is usually a synthetic plastic material that stops sodium, chlorine, and even the larger molecules such as urea, bacteria, and viruses. The reverse osmosis drinking water systems also help in removing lead, arsenic, copper, chromium, selenium, fluoride etc.
10. Aquarium Filters
Having an aquatic pet is quite a messy responsibility. In order to keep their habitat clean, aquarium filters are installed in their tank or aquaria. Aquarium filters are critical components of both freshwater and marine aquaria. Generally, aquatic animals in an aquarium produce waste from excrement and respiration. Another source of waste is uneaten food or plants and fish which have died. These waste products collect in the tanks and contaminate the water. As the degree of contamination rises, the risk to the health of the aquaria increases, and removal of the contamination becomes critical. The filtration of aquarium water is composed of three types of processes: mechanical filtration, biological filtration, and chemical filtration.
- Mechanical Filtration: Mechanical filtration, also known as physical or particulate filtration, is provided by pushing the water through some form of filter media that acts as a strainer. Certain impurities are physically removed from the water column. This is achieved with the help of a sponge or foam, a very fine mesh or net (often called a “sock” for certain filter designs), the gravel in your tank (when using an under gravel filter), or some other similar method. The water circulates through it, and large impurities are trapped. You can then remove them by replacing or cleaning the filter media, or they may break down and have to be removed in other ways.
- Biological Filtration: Biological filtration refers to the mechanism by which beneficial bacteria break down ammonia and nitrite and convert it into a much less harmful nitrate compound. For beneficial bacteria to survive, oxygen-rich water is required, as well as the surface to which bacteria can be attached, such as rocks or sand. All aquariums should have some provisions for biological filtration, and with very limited numbers of fish, this alone might be sufficient to maintain the aquarium.
- Chemical Filtration: Chemical filtration is provided by carbon or chemical resins that extract toxins from the water. Activated filter carbon aggressively remove chemicals from your water until the carbon becomes saturated. However, any activated filter carbon in your filtration system must be changed often.
11. Büchner funnel
If you ever had an opportunity to work in a chemistry lab, you might have come across this cylindrical piece of laboratory equipment known as the Büchner funnel. It is the most commonly used equipment for vacuum filtration in the lab. Traditionally the Büchner funnel is made up of porcelain, but glass and plastic funnels can also be found in the market. The top of the funnel-shaped part is a cylinder with a fritted glass disc/perforated plate separating it from the funnel. The process of filtration in the Büchner funnel is quite similar to the Hirsch funnel or a simple funnel with a filter paper. However, the main advantage of using the Büchner funnel is that it proceeds much more quickly (several orders of magnitude) than simply allowing the liquid to drain through the filter medium via the force of gravity. Combined with that, the vacuum suction allows the wet recrystallized compound to dry out such that the pure dried crystal compound is left remaining. Nevertheless, great care is required while working with the vacuum as it can draw the undesirable liquid. It is mostly used in organic chemistry labs to assist in collecting recrystallized compounds. There is also a more advanced version of this funnel known as the Nutsche Filter, which is mostly used in industries and can work either under vacuum or under pressure.