Filtration systems are used residentially, commercially, and industrially to physically remove contaminants from air, liquid, gas, or powdered substances. The process of separating a fluid substance into two or more distinct factions is often accomplished through the use of a screen, film, or membrane. The fluid may be vacuum or pressure driven, or gravity fed through the filtration device to remove particles or contamination. Other methods of filtration include centrifugation, and chemical, biological, or electrical processing.
Air and water are the most common fluids to go through the filtration process. Other process fluids include food and beverage products, petrochemicals, paints, plating solutions, photographic solutions, pharmaceutical products, chemicals, lubricants, gases, fuels, coolant, and cosmetics.
Quick Links to Filtration Systems Information
The History of Filters
Hieroglyphs from ancient Egyptian tombs show evidence that sand was used to filter drinking water as early as the 15th century B.C.
Hippocrates spoke of bathing as being important to balancing the Four Humors; blood, yellow bile, black bile, and phlegm. He was known to boil water and pour it through a cloth bag called the Hippocratic Sleeve.
Gerber, an Arabian alchemist, described the use of crude stills to purify water in the 8th century.
In 1627, Sir Francis Bacon experimented with desalination of seawater through the use of sand filtration, but was not successful. His findings did fuel an interest in the subject however, and ultimately influenced Antonie van Leeuwenhoek and Robert Hooke to invent and use the microscope to examine waterborne pathogens.
Reverse Osmosis was first observed in a laboratory by Jean-Antoine Nollet in 1748. It would not come into common use for another two centuries.
The first effective use of sand filters was documented in Paisley, Scotland in 1804. John Gibb, the owner of a bleachery, discovered a way to get rid of his surplus by using it to purify and sell water. Over the course of two decades the process was refined and in 1839 London's Chelsea Waterworks became the first public water treatment system.
In 1854, John Snow was able to prove the value of water purification during an outbreak of cholera. In 1855 the first municipal water standards were implemented and by 1858, water purity standards were being set forth throughout Great Britain.
Water softening through the use of sodium ionization to remove minerals, such as calcium and lead, was developed and marketed in 1903.
The U.S. adopted drinking water standards by 1914, but it was not until the 1940s that widespread regulations were instated. The Clean Water Act was passed in 1972, requiring industrial facilities to improve waste procedures, ensuring the safety and cleanliness of public water sources. In 1974, the Safe Drinking Water Act was adopted by all fifty states.
Studies at the University of California Los Angeles, in the 1950s, developed the use of interfacial polymerization to create high flux membranes that allowed low salt passage, facilitating efficient desalination of seawater. These studies in reverse osmosis were continued by the University of Florida, and in 1977, Cape Coral, Florida became the first municipality to utilize 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
There are several different manners in which filtration systems separate materials in a mixed process stream. Membrane filtration involves the use of media that trap contaminants. Foams and other materials employ similar techniques; additional filtration options include the use of gravity, centrifugal force, chemical solvents, biological agents and even electrically charged apparatus. Gravity and centrifugal force filters use hydrostatic or rotational pressures, which remove heavier particles from the flow line. Chemical filters function by either dissolving specific contaminants or attracting them and, through the use of gravity, pulling them from the system. Not as common, but thoroughly effective, biological filters use digestive microbes to remove unwanted organic compounds. There are two main types of filtration systems that depend upon the use of electrical charges to purify air and fluid supplies. Electrodialysis (ED) uses membranes that allow the passage of either positively or negatively charged ions while excluding the passage of the opposite. Because ED membranes are easily clogged, many filters are equipped with electrodialysis reversal (EDR) systems instead. It works in the same way as ED systems, but it periodically reverses the electrical current in order to exchange the fresh product flow. Reverse osmosis (RO), electrodeionization (EDI) and ultrafication (UF) processes are less common but equally efficient options. Each type has benefits and advantages particular to specific filtration applications.
Industrial and municipal water filtration facilities utilize a variety of filter combinations to treat freshwater for consumption and wastewater for safe disposal. The types of water filters used depend on the quantity of water being processed, whether it is a single batch or a continuous stream, the size, shape, quantity, and content of the suspended solids, and the acceptable purity levels of the end product.
- Raw Water Filtering
- Raw water passes through a series of screens and sand to remove larger particles and debris. It continues to travel through filters that remove progressively smaller contaminants until it reaches a specified state of purity. Bag filters and cartridge filters will remove the finest particles. If there are chemical contaminants in the water, other methods may be required to remove them.
- Reverse Osmosis
- The process of forcing a solute fluid through a semipermeable membrane at high pressure to remove ions, molecules, bacteria or other contaminants. It is primarily used to desalinate seawater. As the water passes through the membrane, at pressures up to 1200 psi, the salt is removed, making it potable.
- Uses centrifugal force to separate heavy molecular compounds from a solution. As the centrifuge spins, the solids are driven to the outside and downward, through a spout and form "cake", which may be disposed of or used for other purposes. The purified solution can then be decanted or transferred.
- Centrifugation is used with gelatinous solutions or those with fine particles. It is used for wastewater treatment, to remove milk solids from whole milk, to clarify wine, and in uranium enrichment processes. Ultra-centrifugation is used in biological research. Medical filtration systems must be able to provide microscopic separation. Blood-, air-, and water-borne pathogens must be isolated and contained.
- Air Filtration Systems
- May include individual breathing devices, such as dust masks, respirators, or oxygen breathing apparatus (OBA). They may provide fresh, heated, or cooled air for buildings, mines, and other occupied spaces, or may scrub air pollution from industrial exhaust.
- Many air filters are complex fiber layers that keep dust and fumes from passing through by trapping it between fibers. In some instances, a chemical cleaning process is necessary to make the air safe. The air is decontaminated as it flows through filtration media consisting of granules of zeolite or activated carbon. The porous pellets scrub gaseous pollutants by creating an ion exchange, chemical bonding, or molecular destruction of the contaminants.
- Powdered Materials Filtration
- Powdered materials, such as flour, cosmetic products, medications, paints, and dyes, are filtered through a series of screens or perforated material to remove larger pieces for reprocessing. Minerals can be refined from ore to molecular powders in a progression of grinding and filtration. Gemstones are screened from the dirt matrix by sifting through progressively smaller mesh.
Filtration System Types
- Air Filtration Systems
- Cleanse, purify and reduce the overall number of particulates and other impurities present in an air source.
- Cartridge Filtration
- Involves the use of a porous cartridge filter, commonly made of polypropylene (PP) or ceramic, which catches particles as liquids pass through it. Cartridge filtration is an easy filtration method, but it is not suitable for liquids with high turbidity and fouling remains a common problem leading to filter replacement.
- Centrifugal Separators
- Also called "centrifugal filters" or "cyclone separators," use cyclones in which substances, such as immiscible liquids, gases and solids, are separated during rapid rotation from the contaminated fluid. The rotation of the cyclone is caused by the entrance of the pressurized fluid from which the contaminants must be removed.
- Chemical Filtration
- Removes contaminants through the use of a chemical medium, such as activated carbon, in the filter. Chemical filtration remains common in the filtration of gases.
- Coalescing Filters
- Specialized filter media designed to collect and remove oil and other vapors or mists from process air streams.
- Depth Filters
- Granular substance, such as diatomaceous earth, sand, or carbon, that traps particles in the mass as the fluid passes through. This process is commonly used in swimming pool filters. It is typically less expensive and less likely to clog than a solid filter, and the filter medium is usually easy to dispose of.
- Dual-Media and Multi-Media Filters
- Use more than one substance to accomplish specified purification levels. These may be multiple layers of increasingly dense filtration media or granular media sandwiched between membranes. These combinations may be treated with a compound that incorporates a chemical reaction with a physical barrier.
- Electrostatic Filtration
- A filtering process that involves electrically charged media that use an electric field to filter substances and remove particles as small as .01 micrometers in size. As the substances pass through the charged media, certain particles are attracted to the charged media.
- Filter Media
- Fibrous or porous materials composed of fine or coarse semi-permeable matrices that trap or chemically dissolve particles while allowing the base product, gas or fluid, to pass through.
- Filtering Systems
- Encompass a wide range of products and equipment designed to purify, clarify and remove suspended debris from fluid and gaseous process streams.
- Filtration Equipment
- Includes filters, strainers, and housings.
- Filtration Products
- Used in a number of industrial, commercial and residential applications to reduce or eliminate unwanted particles from a fluid or gaseous process flow. These items are widely available and include both the filter media and housing assemblies used to hold them in place.
- High Efficiency Particulate Air Filters (HEPA)
- Layered fiber filters that remove pollutants from air by acting as a sieve. The particles are intercepted by the fibers, impact the fibers and are unable to travel further, or are diffused by electrostatic attraction. HEPA filters are used in vacuum cleaning systems, airplane cabin air circulating systems, and respirators. They are capable of removing up to 99.999995 percent of particles and contaminants from the air that passes through them. They must meet standards as set forth by the National Institute for Occupational Safety and Health (NIOSH) and the U.S. Department of Energy (DOE).
- Industrial Filters
- Heavy duty filtration systems that serve to effectively remove particulates and suspended debris from process streams as well as the air and fluid flow lines of manufacturing operations and facilities.
- Liquid Filtration
- May involve the removal of particles from a liquid, known as "liquid-solid filtration," or the separation of liquids from gases, known as "gas-liquid filtration."
- Membrane Filtration
- Involves the use of a membrane as the filter media to allow the passage of substances such as air and water while preventing the passage of other substance particles. Membrane filters are small and automated and used for applications that include purifying blood during dialysis treatments, removing bacteria and odors and desalinating water.
- Type of membrane filtration used to remove extremely small particles. The effectiveness of nanofiltration lies between that of reverse osmosis and ultrafiltration.
- Oil Filtration
- Necessary to remove particles and contamination that may hinder the functioning of equipment. Oil filtration remains common in the automotive/trucking and agricultural industries as well as other industries that utilize equipment requiring the use of motor, hydraulic and other types of oils.
- Pressure Filters
- These filtration products that employ compressed air or pressurized fluid as the principle means of moving a process stream through filter media in order to separate materials and remove suspended debris.
- Particulate Filters
- Function as fluid flows from the high pressure side of the filter medium to the low pressure side. The fluid may be pumped through the system, such as a gas pump, or gravity fed, like a coffee maker.
- Reverse Osmosis
- Type of filtration method in which water is pushed under pressure through a membrane, while contaminants are prevented from passing through the filter. Filtered contaminants include sodium, phosphorus, aluminum, lead and fluoride.
- Surface Filter
- A screen or strainer through which fluids pass and particles remain trapped in the filter. This mass transfer process may be used to sort or separate materials of different sizes or to remove unwanted particles from the fluid. The filters may be cleaned by physically removing the material, washing with solvent or detergent, or by backwashing; reversing the flow to dislodge particles.
- Surface filters include bag filters, cartridge filters, strainers, screens, and membranes. They may be made from plastic, polymers, rubber, cloth, fiberglass, or stainless steel. Bag and cartridge filters are installed inside removable housings that typically screw into orifices in the filtration systems that the fluid must pass through. Coalescing filters remove oil and vapor from air streams by adsorption. As air passes through the fiber membranes, the contaminants "coalesce" onto the fibers, collecting and draining away, as the clean air continues to flow.
- Water Filtering Systems
- Involve the purification of water for drinking purposes. Wastewater is also filtered to remove excess particles.
- Wet or Dry Filtration
- Biological filtration process involving the exposure of the filter medium to air to facilitate nitrification. Wet/dry filters are commonly used in aquariums.
- Type of membrane filtration that removes particles ranging from 0.002 to 0.1 micrometers in size. Filtered substances include bacteria and viruses.
Uses for Filtration Systems
Residential filters are typically HVAC ducting filters that remove dust and allergens from the air in homes and aeration screens on tap water faucets, although some homes are equipped with water softening and purification systems that remove minerals, chemicals, or bacteria.
Most hikers and campers are familiar with water filters that pump raw water through a ceramic filter. These simple filters have micro-pores as small as .2 microns, through which no waterborne pathogen, such as Giardia or Cryptosporidium, can pass. They may be treated with colloidal silver, which acts as a chemical filtration device.
Automobiles have filter systems for intake air, exhaust, oil, brake fluid, transmission fluid, antifreeze, refrigerant, and coolant (you can find companies who manufacture them here).
Industrial filtration systems are found in pipelines, power plants, aviation, aeronautics, oil and gas refining, wood, metal and plastic manufacturing. Commercial filtration systems encompass a wide variety of circumstances that require specific types of filtering capabilities and methods dependent upon the material involved.
Fresh water for municipal use must be purified to meet safe standards for consumption. You can find water filtering system manufacturers that can help you purify your water to these standards here on IQS Directory. In addition to potable water, sewage and storm water must also be processed to satisfactory degrees for environmental safety. Manufacturing plants must meet clean air standards for employee comfort, health, and safety, and factory exhaust, in addition to meeting clean water standards for any residual wastewater resulting from production.
Things to Consider When Purchasing Filtration Systems
Which filter system to use is entirely dependent on the material or solution being processed. Liquids that are not gravity fed into the system or that require pressure to accomplish filtration, will need an adequate pump to move them through the pipes or tubes that contain them. Reservoirs to contain contaminated liquid, filtered liquid, and contaminants may be required. Lifts or conveyors may be necessary to move the product.
Swimming pools, hot tubs, and water softening treatment systems typically come with standard filter system packages that are easy to install and use. Larger filtration systems can be designed for specific volume, pressure, solute quantity, quality, use or disposal. Commercial water treatment, pharmaceutical, cosmetic, food or beverage processing will require engineering and design to meet NIOSH, NSF, and ANSI standards for purity and safety.
Some cutting oils, coolant oils, and lubricant oils may be filtered and reused many times. Oil filtration systems may be required to meet certain industrial standards, including ANSI, OSHA, or ISO, depending upon their composition or use.
An industrial design team can put together the right system for each purpose and to meet required standards. Consideration will be given to the type of fluid being filtered. These factors will include whether it is liquid, air, or powder, corrosive, conductive, volatile, noxious, hot, cold, or presents risk to health and safety. Other considerations include the volume and viscosity of inflow, and how often or consistently the system will be operating.
A good design will maximize utility and minimize downtime from problems with fouling or routine maintenance. A good design team will understand the needs and requirements of the system and provide the most cost effective unit that meets those needs. They will offer service and support, as well as options for future expansion.
Filtration System Terms
- The outlet located at the bottom of a cyclone.
- The use of rotational forces to separate liquids and solids.
- The neutralization of the electrical charges on fine particles in water using chemicals called coagulants. The coagulants cause the particles to clump together, and the clumps are then skimmed or drained off or filtered from the water.
- Collecting Efficiency
- The capability of a device to capture and retain particles.
- Removing the top layer of a fluid after the heavier material, which can be either a solid or a denser liquid, has settled.
- Act of removing dissolved mineral salts from water.
- Dense Membrane
- A non-porous membrane.
- The treated substance that emerges from the filtration system.
- Any liquid, gaseous or vapor substance.
- The amount or volume of a substance passing through a given unit of a membrane or filter in a given amount of time.
- The clogging of membrane filters due to the buildup of particles on the membrane and in the membrane pores.
- Homogeneous Membrane
- A membrane in which the properties remain the same throughout the substance.
- The substance that enters the filtration system to be filtered.
- A film structure, having a thickness greater than its lateral measurements, through which substances flow as the chemical separation of substance particles occurs.
- The process of passing a fluid through a membrane to increase fluid concentration.
- Osmotic Pressure
- The superficial hydrostatic pressure on a semi-permeable membrane caused by osmosis.
- The stream of fluid that leaves the cyclone through the vortex finder.
- The ability of a fluid substance 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 suitable for drinking.
- Ppm (Parts per Million)
- Unit of measurement indicating one part per every million parts of air, water, etc.
- A liquid containing suspended solids.
- Filtration mechanism for the removal of coarse particles from liquid substances. Strainers usually function as an initial filtration method used prior to other filters that remove smaller particles.
- Vortex Finder
- The outlet at the top of the cyclone through which overflow exits.