Filtration Systems
Filtration systems are employed across residential, commercial, and industrial settings to effectively remove contaminants from air, liquid, gas, or powdered substances. The process of separating a fluid into distinct factions is typically achieved through the use of screens, films, or membranes. These fluids can be driven through the filtration device by vacuum, pressure, or gravity to eliminate particles or impurities. Additional filtration methods include centrifugation, as well as chemical, biological, or electrical processing.
While air and water are the most commonly filtered fluids, various other substances also undergo filtration. These include food and beverage products, petrochemicals, paints, plating solutions, photographic solutions, pharmaceuticals, chemicals, lubricants, gases, fuels, coolants, and cosmetics.
The History of Filters
Hieroglyphs from ancient Egyptian tombs suggest that sand was used to filter drinking water as early as the 15th century B.C.
Hippocrates, emphasizing the importance of balancing the Four Humors—blood, yellow bile, black bile, and phlegm—was known to boil water and pour it through a cloth bag, referred to as the Hippocratic Sleeve.
In the 8th century, Arabian alchemist Gerber described the use of crude stills to purify water.
In 1627, Sir Francis Bacon conducted experiments with sand filtration for desalination, though his attempts were unsuccessful. His work sparked interest in the subject, eventually leading Antonie van Leeuwenhoek and Robert Hooke to use microscopes to study waterborne pathogens.
Reverse osmosis was first observed in a laboratory setting by Jean-Antoine Nollet in 1748, though it would take nearly two centuries before it became widely used.
The first successful application of sand filters was recorded in Paisley, Scotland, in 1804. John Gibb, a bleachery owner, found a way to use surplus sand to purify and sell water. Over the next two decades, the process was refined, and in 1839, London's Chelsea Waterworks became the first public water treatment system.
In 1854, John Snow proved the effectiveness of water purification during a cholera outbreak. By 1855, municipal water standards were implemented, and by 1858, water purity regulations were established across Great Britain.
Water softening using sodium ionization to remove minerals like calcium and lead was developed and introduced to the market in 1903.
The U.S. adopted drinking water standards in 1914, but it wasn't until the 1940s that widespread regulations were enforced. The Clean Water Act of 1972 required industrial facilities to improve waste management, ensuring the safety and cleanliness of public water sources. In 1974, the Safe Drinking Water Act was adopted nationwide.
In the 1950s, studies at the University of California, Los Angeles, led to the development of interfacial polymerization to create high-flux membranes that allowed low salt passage, enhancing seawater desalination. The University of Florida continued this research, and in 1977, Cape Coral, Florida, became the first municipality to use reverse osmosis on a commercial scale. By 1985, Cape Coral was producing up to 15 million gallons of potable water per day.
Separating Materials Through Filtration
Filtration systems use various methods to separate materials from a mixed process stream. Membrane filtration employs media that capture contaminants, while foams and other materials use similar techniques. Additional filtration methods include gravity, centrifugal force, chemical solvents, biological agents, and electrically charged devices. Gravity and centrifugal filters utilize hydrostatic or rotational pressures to remove heavier particles from the flow. Chemical filters work by dissolving or attracting contaminants, then using gravity to pull them out of the system. Less common but highly effective biological filters use digestive microbes to eliminate organic compounds. Two types of filtration systems that rely on electrical charges to purify air and fluids are electrodialysis (ED) and reverse osmosis (RO). ED uses membranes to allow the passage of either positively or negatively charged ions, while excluding the opposite. Due to clogging, electrodialysis reversal (EDR) systems are often employed, which periodically reverse the electrical current to refresh the flow. Other advanced methods like electrodeionization (EDI) and ultrafiltration (UF) also provide efficient filtration. Each method offers specific advantages suited to different applications.
Industrial and municipal water filtration systems use various combinations of filters to treat freshwater for consumption and wastewater for safe disposal. The choice of water filters depends on the water quantity being processed, whether it is a batch or continuous stream, the size, shape, quantity, and content of suspended solids, and the required purity level of the final product.
Raw Water Filtering
Raw water is first passed through screens and sand to remove larger particles and debris. It then progresses through filters that remove smaller contaminants until it reaches the required level of purity. Bag and cartridge filters are used to remove the finest particles. If chemical contaminants are present, additional methods may be necessary for removal.
Reverse Osmosis
Reverse osmosis involves forcing a solution through a semipermeable membrane at high pressure to remove ions, molecules, bacteria, and other contaminants. This method is mainly used for desalination, particularly for seawater. The water passes through the membrane under pressure (up to 1200 psi), removing the salt and making it safe for consumption.
Centrifugation
Centrifugation uses centrifugal force to separate heavy compounds from a solution. As the centrifuge spins, solids are pushed to the outer edge and form a "cake" that can be disposed of or reused. The purified solution is then decanted or transferred. Centrifugation is used in applications like wastewater treatment, milk solid removal, wine clarification, and uranium enrichment. Ultra-centrifugation is especially important in biological research and medical filtration systems, which require microscopic separation to isolate pathogens from air, blood, or water.
Air Filtration Systems
Air filtration systems can range from personal breathing devices like dust masks and respirators to large systems for industrial exhaust or building ventilation. Some air filters consist of complex fiber layers that trap dust and fumes between fibers. In certain cases, chemical cleaning is necessary to purify the air. Filtration media such as zeolite or activated carbon granules scrub gaseous pollutants by ion exchange, chemical bonding, or molecular destruction.
Powdered Materials Filtration
Powdered materials like flour, cosmetics, medications, paints, and dyes are filtered through screens or perforated materials to remove larger particles for reprocessing. Mineral refining from ore to molecular powders involves grinding and filtration stages. Similarly, gemstones are separated from their matrix through progressively smaller mesh screening.
Filtration System Types
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Air Filtration Systems
These systems cleanse and purify air by reducing the number of particulates and other impurities present.
Cartridge Filtration
Uses a porous filter, typically made from polypropylene (PP) or ceramic, to capture particles as liquids pass through. Although simple, it is not suitable for liquids with high turbidity, and fouling remains a common issue leading to filter replacement.
Centrifugal Separators
Also known as centrifugal filters or cyclone separators, these use cyclonic action to separate substances like immiscible liquids, gases, and solids during rapid rotation. The rotating cyclone is powered by the pressurized fluid that needs its contaminants removed.
Chemical Filtration
This process removes contaminants using a chemical medium, such as activated carbon, within the filter. It is commonly used in the filtration of gases.
Coalescing Filter
Specially designed filters that collect and remove oil and other vapors or mists from process air streams.
Depth Filters
Composed of granular materials like diatomaceous earth, sand, or carbon, these filters trap particles as fluid passes through. They are often used in swimming pool filters, are less likely to clog, and are easier to dispose of compared to solid filters.
Dual-Media and Multi-Media Filters
Utilize multiple substances to achieve specific purification levels. These filters may have several layers of progressively denser media or granular media sandwiched between membranes, often treated with a compound that triggers a chemical reaction with physical barriers.
Electrostatic Filtration
This process uses electrically charged media that filter substances by creating an electric field to remove particles as small as 0.01 micrometers. The charged media attracts certain particles during the filtration process.
Filter Media
Fibrous or porous materials, typically semi-permeable, designed to trap or chemically dissolve particles while allowing fluids or gases to pass through.
Filtering Systems
A broad range of products and equipment designed to purify, clarify, and remove suspended debris from fluid and gas streams.
Filtration Equipment
Includes various filters, strainers, and housings used in filtration systems.
Filtration Products
Widely used in industrial, commercial, and residential applications, these products help reduce or eliminate unwanted particles from a fluid or gas flow. They include filter media and housing assemblies.
High Efficiency Particulate Air Filters (HEPA)
These layered fiber filters trap pollutants and particles as small as 0.3 microns, intercepting particles through physical contact or electrostatic attraction. HEPA filters are used in systems like vacuum cleaners, airplane cabins, and respirators, and can remove up to 99.9995% of particles from the air. They must meet standards from agencies like NIOSH and the U.S. Department of Energy.
Industrial Filters
Heavy-duty filtration systems that effectively remove particulates from air and fluid flow lines in manufacturing facilities and operations.
Liquid Filtration
Can either involve liquid-solid filtration, removing particles from a liquid, or gas-liquid filtration, which separates liquids from gases.
Membrane Filtration
Involves using a membrane to filter substances such as air and water while preventing unwanted particles from passing through. This process is often used for applications like blood purification during dialysis, bacteria removal, and water desalination.
Nanofiltration
A type of membrane filtration used to remove very small particles. Its effectiveness falls between reverse osmosis and ultrafiltration.
Oil Filtration
Removes particles and contaminants from oils, which is important for the functioning of machinery. It is common in industries like automotive and agriculture, where oils are essential for operations.
Pressure Filters
These filtration products use compressed air or pressurized fluid to push a process stream through filter media, separating materials and removing debris.
Particulate Filters
Work by allowing fluid to flow from the high-pressure side of the filter medium to the low-pressure side. The fluid may be pumped through or gravity-fed, like in a coffee maker.
Reverse Osmosis
A filtration method in which water is forced through a membrane under pressure, removing contaminants such as sodium, phosphorus, aluminum, lead, and fluoride.
Surface Filter
A screen or strainer that traps particles while allowing fluid to pass through. Methods for cleaning these filters include physically removing material, washing with solvents or detergent, or backwashing.
Water Filtering Systems
Used to purify water for drinking and to filter wastewater for safe disposal.
Wet or Dry Filtration
Biological filters used in aquariums that expose filter media to air for nitrification, facilitating the purification of water in aquatic environments.
Ultrafiltration
A type of membrane filtration that removes particles as small as 0.002 to 0.1 micrometers, filtering out bacteria and viruses.
Uses for Filtration Systems
Residential filters are commonly used in HVAC ducting to remove dust and allergens from indoor air, as well as in aeration screens on tap water faucets. Some homes also have water softening and purification systems that filter out minerals, chemicals, or bacteria.
Water filters used by hikers and campers are typically portable, pumping raw water through a ceramic filter with micro-pores as small as 0.2 microns. These filters are effective at preventing waterborne pathogens such as Giardia and Cryptosporidium from passing through. Many of these filters are treated with colloidal silver to enhance their chemical filtration capabilities.
Automobiles rely on a variety of filters, including systems for intake air, exhaust, oil, brake fluid, transmission fluid, antifreeze, refrigerant, and coolant, all of which can be sourced from specialized manufacturers.
Industrial filtration systems are widely used in pipelines, power plants, aviation, aeronautics, and in industries such as oil and gas refining, and wood, metal, and plastic manufacturing. Commercial filtration systems vary based on the specific requirements of the material being filtered, and the filtration methods employed depend on these materials.
Municipal fresh water must undergo purification to meet safety standards for consumption. Manufacturers specializing in water filtration systems can help purify water to meet these standards. Additionally, sewage and storm water must be treated to ensure environmental safety. Manufacturing plants must comply with clean air standards to protect employee health and comfort, while also ensuring that factory exhaust systems and any residual wastewater meet clean water standards.
Things to Consider When Purchasing Filtration Systems
The choice of filter system depends entirely on the material or solution being processed. Liquids that are not gravity-fed or require pressure for filtration will need an appropriate pump to move them through the pipes or tubes. Reservoirs may be needed to contain contaminated liquid, filtered liquid, and contaminants. Lifts or conveyors could also be necessary to move the product efficiently.
For smaller systems like swimming pools, hot tubs, or water softening treatments, standard filter systems are typically included, making them easy to install and use. Larger filtration systems, however, need to be designed to handle specific factors such as volume, pressure, solute quantity, quality, and disposal needs. Industries like commercial water treatment, pharmaceuticals, cosmetics, and food or beverage processing require systems engineered to meet safety and purity standards such as those set by NIOSH, NSF, and ANSI.
Certain oils, such as cutting oils, coolant oils, and lubricant oils
, may be filtered and reused multiple times. Oil filtration systems often need to meet industrial standards, including ANSI, OSHA, or ISO, depending on their specific composition and use.
An industrial design team will develop the right filtration system for each purpose, ensuring that it meets the necessary standards. Considerations will include the type of fluid being filtered, whether it is liquid, air, or powder, and whether it is corrosive, conductive, volatile, or hazardous. Other factors such as the volume, viscosity of the inflow, and frequency of operation will also be taken into account.
A well-designed system will maximize efficiency while minimizing downtime caused by fouling or maintenance issues. A competent design team will understand the specific needs of the filtration process and provide the most cost-effective solution that meets those needs. They will also offer ongoing service and support, as well as options for future expansion.
Filtration System Terms
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Apex
The outlet located at the bottom of a cyclone.
Centrifugation
The process of using rotational forces to separate liquids and solids.
Coagulation
The process of neutralizing the electrical charges on fine particles in water using chemicals called coagulants. These coagulants cause the particles to clump together, and the clumps are then skimmed, drained, or filtered from the water.
Collecting Efficiency
The ability of a device to capture and retain particles.
Decantation
The process of removing the top layer of a fluid after the heavier material, which can be either a solid or a denser liquid, has settled.
Demineralization
The process of removing dissolved mineral salts from water.
Dense Membrane
A non-porous membrane.
Effluent
The treated substance that emerges from the filtration system.
Fluid
Any substance in a liquid, gaseous, or vapor form.
Flux
The volume or amount of a substance passing through a given unit of a membrane or filter over a specific amount of time.
Fouling
The clogging of membrane filters due to the buildup of particles on the membrane and within its pores.
Homogeneous Membrane
A membrane in which the properties remain consistent throughout the material.
Influent
The substance that enters the filtration system to be filtered.
Membrane
A thin film structure, thicker than its lateral measurements, through which substances flow as particles are chemically separated.
Osmosis
The process of passing a fluid through a membrane to increase the concentration of the fluid.
Osmotic Pressure
The hydrostatic pressure on a semi-permeable membrane caused by the process of osmosis.
Overflow
The stream of fluid that exits the cyclone through the vortex finder.
Permeability
The ability of a fluid to pass through a material. Filters have varying degrees of permeability that allow substances of different sizes to pass through them.
Potable Water
Water that is safe and suitable for drinking.
Ppm (Parts per Million)
A unit of measurement indicating one part per every million parts of a substance, such as air or water.
Slurry
A mixture of liquid and suspended solids.
Strainer
A filtration mechanism used to remove coarse particles from liquids. Strainers typically function as an initial filtration method before finer filters are used to remove smaller particles.
Vortex Finder
The outlet at the top of the cyclone through which overflow exits.
