Filtration is a physical separation process that separates solid matter and fluid from a mixture using a filter medium that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter medium are described as oversize and the fluid that passes through is called the filtrate. Oversize particles may form a filter cake on top of the filter and may also block the filter lattice, preventing the fluid phase from crossing the filter, known as blinding. The size of the largest particles that can successfully pass through a filter is called the effective pore size of that filter. The separation of solid and fluid is imperfect; solids will be contaminated with some fluid and filtrate will contain fine particles. Filtration occurs both in nature and in engineered systems; there are biological, geological, and industrial forms.
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for human consumption, but water purification may also be carried out for a variety of other purposes, including medical, pharmacological, chemical, and industrial applications. The history of water purification includes a wide variety of methods. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination; and the use of electromagnetic radiation such as ultraviolet light.
Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, including being safely returned to the environment. Water treatment removes contaminants and undesirable components, or reduces their concentration so that the water becomes fit for its desired end-use. This treatment is crucial to human health and allows humans to benefit from both drinking and irrigation use.
In the oil industry, waterflooding or water injection is where water is injected into the oil reservoir, to maintain the pressure, or to drive oil towards the wells, and thereby increase production. Water injection wells may be located on- and offshore, to increase oil recovery from an existing reservoir.
A constructed wetland is an artificial wetland to treat sewage, greywater, stormwater runoff or industrial wastewater. It may also be designed for land reclamation after mining, or as a mitigation step for natural areas lost to land development. Constructed wetlands are engineered systems that use the natural functions of vegetation, soil, and organisms to provide secondary treatment to wastewater. The design of the constructed wetland has to be adjusted according to the type of wastewater to be treated. Constructed wetlands have been used in both centralized and decentralized wastewater systems. Primary treatment is recommended when there is a large amount of suspended solids or soluble organic matter.
Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans. This applies to industries that generate wastewater with high concentrations of organic matter, toxic pollutants or nutrients such as ammonia. Some industries install a pre-treatment system to remove some pollutants, and then discharge the partially treated wastewater to the municipal sewer system.
Sand filters are used as a step in the water treatment process of water purification.
In terms of water treatment, including water purification and sewage treatment, backwashing refers to pumping water backwards through the filters media, sometimes including intermittent use of compressed air during the process. Backwashing is a form of preventive maintenance so that the filter media can be reused. In water treatment plants, backwashing can be an automated process that is run by local programmable logic controllers (PLCs). The backwash cycle is triggered after a set time interval, when the filter effluent turbidity is greater than a treatment guideline or when the differential pressure across the filter exceeds a set value.
Electrocoagulation (EC) is a technique used for wastewater treatment, wash water treatment, industrially processed water, and medical treatment. Electrocoagulation has become a rapidly growing area of wastewater treatment due to its ability to remove contaminants that are generally more difficult to remove by filtration or chemical treatment systems, such as emulsified oil, total petroleum hydrocarbons, refractory organics, suspended solids, and heavy metals. There are many brands of electrocoagulation devices available, and they can range in complexity from a simple anode and cathode to much more complex devices with control over electrode potentials, passivation, anode consumption, cell REDOX potentials as well as the introduction of ultrasonic sound, ultraviolet light and a range of gases and reactants to achieve so-called Advanced Oxidation Processes for refractory or recalcitrant organic substances.
The rapid sand filter or rapid gravity filter is a type of filter used in water purification and is commonly used in municipal drinking water facilities as part of a multiple-stage treatment system. These systems are complex and expensive to operate and maintain, and therefore less suitable for small communities and developing nations.
In chemical engineering, biochemical engineering and protein purification, crossflow filtration is a type of filtration. Crossflow filtration is different from dead-end filtration in which the feed is passed through a membrane or bed, the solids being trapped in the filter and the filtrate being released at the other end. Cross-flow filtration gets its name because the majority of the feed flow travels tangentially across the surface of the filter, rather than into the filter. The principal advantage of this is that the filter cake is substantially washed away during the filtration process, increasing the length of time that a filter unit can be operational. It can be a continuous process, unlike batch-wise dead-end filtration.
Swimming pool sanitation is the process of ensuring healthy conditions in swimming pools. Proper sanitation is needed to maintain the visual clarity of water and to prevent the transmission of infectious waterborne diseases.
River Bank filtration is a type of filtration that works by passing water to be purified for use as drinking water through the banks of a river or lake. It is then drawn off by extraction wells some distance away from the water body. The process may directly yield drinkable water, or be a relatively uncomplicated way of pre-treating water for further purification.
Depth filters are filters that use a porous filtration medium to retain particles throughout the medium, rather than just on the surface of the medium. Depth filtration, typified by multiple porous layers with depth, is used to capture the solid contaminants from the liquid phase. These filters are commonly used when the fluid to be filtered contains a high load of particles because, relative to other types of filters, they can retain a large mass of particles before becoming clogged.
A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Biological membranes include cell membranes ; nuclear membranes, which cover a cell nucleus; and tissue membranes, such as mucosae and serosae. Synthetic membranes are made by humans for use in laboratories and industry.
Spa filters work continuously to keep debris and sediments from the water in a spa pool.
Gravity filtration is a method of filtering impurities from solutions by using gravity to pull liquid through a filter. The two main kinds of filtration used in laboratories are gravity and vacuum/suction. Gravity filtration is often used in chemical laboratories to filter precipitates from precipitation reactions as well as drying agents, inadmissible side items, or remaining reactants. While it can also be used to separate out strong products, vacuum filtration is more commonly used for this purpose.
The Coppermills Water Treatment Works is a large water treatment works in the Lea Valley in east London. Completed in 1969 by the Metropolitan Water Board, it is now owned and operated by Thames Water. In 2009, Coppermills was connected to the Thames Water Ring Main via the Northern Extension Tunnel, enabling the facility to be a major supplier of water to the whole London area. It is capable of supplying a maximum of 680 million litres of water per day.
Pile Cloth Media Filtration is a mechanical process for the separation of organic and inorganic solids from liquids. It belongs to the processes of surface filtration and cake filtration where, in addition to the sieve effect, real filtration effects occur over the depth of the pile layer. Pile Cloth Media Filtration represents a branch of cloth filtration processes and is used for water and wastewater treatment in medium and large scale. In Pile Cloth Media Filtration, three-dimensional textile fabrics are used as filter media. During the filter cleaning of the pile layer the filtration process continues and is not interrupted.
Diatomaceous earth (DE) filtration is a special filtration process that removes particles from liquids as it passes through a layer of fossilized remains of microscopic water organism called diatoms. These diatoms are mined from diatomite deposits which are located along the Earth's surface as they have accumulated in sediment of open and moving bodies of water. Obtained diatomaceous earth is then purified using acid leaching or liquid-liquid extraction in order for it to be used in any form of application. The process of D.E. filtration is composed of three main stages: pre-coating, body feed, and cleaning.
References Nalco Water, an Ecolab Company. Nalco Water Handbook, Fourth Edition (McGraw-Hill Education: New York, Chicago, San Francisco, Athens, London, Madrid, Mexico City, Milan, New Delhi, Singapore, Sydney, Toronto, 2018). https://www.accessengineeringlibrary.com/content/book/9781259860973
