Water treatment

Source: Wikipedia, the free encyclopedia.
For medical water treatment, see
Water cure (therapy)
.
This article is about treatment of various waters. For treatment of wastewater, see Wastewater treatment.
Dalecarlia Water Treatment Plant, Washington, D.C.

Water treatment is any process that improves the

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.

Types

Drinking water treatment

Main articles: Water purification, Drinking water, and water supply

chemicals, and from various streams such as cooling towers, boilers, and production lines.[1]

Typical drinking water treatment processes

Treatment for

fungi, and minerals including iron and manganese. Research including Professor Linda Lawton's group at Robert Gordon University, Aberdeen is working to improve detection of cyanobacteria.[2] These substances continue to cause great harm to several less developed countries who do not have access to effective water purification systems.[original research?
]

Measures taken to ensure water quality not only relate to the treatment of the water, but to its conveyance and distribution after treatment. It is therefore common practice to keep residual disinfectants in the treated water to kill bacteriological contamination during distribution and to keep the pipes clean.[3]

Water supplied to domestic properties such as for tap water or other uses, may be further treated before use, often using an in-line treatment process. Such treatments can include water softening or ion exchange. [citation needed]

Wastewater treatment

This section is an excerpt from Wastewater treatment.[edit]
Sewage treatment plant (a type of wastewater treatment plant) in Cuxhaven
, Germany

Sewage Treatment. For industrial wastewater, treatment either takes place in a separate Industrial wastewater treatment, or in a sewage treatment plant (usually after some form of pre-treatment). Further types of wastewater treatment plants include Agricultural wastewater treatment and leachate
treatment plants.

Processes commonly used in wastewater treatment include phase separation (such as sedimentation), biological and chemical processes (such as oxidation) or polishing. The main by-product from wastewater treatment plants is a type of sludge that is usually treated in the same or another wastewater treatment plant.[5]: Ch.14  Biogas can be another by-product if anaerobic treatment processes are used. Treated wastewater can be reused as reclaimed water.[6] The main purpose of wastewater treatment is for the treated wastewater to be able to be disposed or reused safely. However, before it is treated, the options for disposal or reuse must be considered so the correct treatment process is used on the wastewater. Bangladesh has officially inaugurated the largest single sewage treatment plant (STP) in South Asia, located in the Khilgaon area of the city. With a capacity to treat five million sewage per day, the STP marks a significant step towards addressing the country's wastewater management challenges.[7]

The term "wastewater treatment" is often used to mean "sewage treatment".[8]

Industrial water treatment

This section is an excerpt from Industrial water treatment § Overview.[edit]

Water treatment is used to optimize most water-based industrial processes, such as heating, cooling, processing, cleaning, and rinsing so that operating costs and risks are reduced. Poor water treatment lets water interact with the surfaces of pipes and vessels which contain it. Steam boilers can scale up or corrode, and these deposits will mean more fuel is needed to heat the same amount of water. Cooling towers can also scale up and corrode, but left untreated, the warm, dirty water they can contain will encourage bacteria to grow, and Legionnaires' disease can be the fatal consequence. Water treatment is also used to improve the quality of water contacting the manufactured product (e.g., semiconductors) and/or can be part of the product (e.g., beverages, pharmaceuticals). In these instances, poor water treatment can cause defective products.[citation needed]

In many cases, effluent water from one process can be suitable for reuse in another process if given suitable treatment. This can reduce costs by lowering charges for water consumption, reduce the costs of effluent disposal because of reduced volume, and lower energy costs due to the recovery of heat in recycled wastewater.
Kokemäki River
is absorbed through the basins into the Virttaankangas ridge formation.

Processes

Empty aeration tank for iron precipitation

For the elimination of hazardous chemicals from the water, many

treatment procedures have been applied.[9]

The processes involved in removing the contaminants include physical processes such as

disinfection and coagulation, and biological processes such as slow sand filtration
.

A combination selected from the following processes (depending on the season and contaminants and chemicals present in the raw water) is used for municipal drinking water treatment worldwide.

Chemical

Tanks with sand filters to remove precipitated iron (not working at the time)

Different chemical procedures for the conversion into final products or the removal of pollutants are used for the safe disposal of contaminants.[10]

  • Pre-chlorination for algae control and arresting biological growth.
  • Aeration along with pre-chlorination for removal of dissolved iron when present with relatively small amounts of manganese.
  • Disinfection for killing bacteria, viruses and other pathogens, using chlorine, ozone and ultra-violet light.

Physical

Physical techniques of water/waste water treatment rely on physical phenomena to complete the removal process, rather than biological or chemical changes.[10]

Most common physical techniques are:

  • Sedimentation is one of the most important main wastewater treatment procedures. Gravity settling is a method of separating particles from a fluid. The particle in suspension remains stable in quiescent conditions due to the decrease in water velocity throughout the water treatment process, following which the particles settle by gravitational force.[11][12] For solids separation that is the removal of suspended solids trapped in the floc.
  • Membrane filtration are the two main forms of waste water filtration.[13]
  • Degasification) is the process of removing dissolved gases from a solution . Henry's law states that the amount of dissolved gas in a liquid is proportionate to the partial pressure of the gas. Degasification is a low-cost method of removing carbon dioxide gas from waste water that raises the pH of the water by removing the gas.[10]
  • Deaerator is used to reduce oxygen and nitrogen in boiler feed water applications.

Physico-chemical

Also referred to as "Conventional" Treatment

  • Coagulation for flocculation. The addition of coagulants destabilizes colloidal suspensions by neutralizing their charges, resulting in the aggregation of smaller particles during the coagulation process.[14]
  • Coagulant aids, also known as polyelectrolytes – to improve coagulation and for more robust floc formation.
  • Polyelectrolytes or also known in the field as polymers, usually consist of either a positive or negative charge. The nature of the polyelectrolyte used is purely based on the source water characteristics of the treatment plant.
  • These will usually be used in conjunction with a primary coagulant such as ferric chloride, ferric sulfate, or alum.

precipitant agent such as lime. In industrial applications stronger alkalis may be used to effect complete precipitation. In drinking water treatment, the common-ion effect is often used to help reduce water hardness.[15]

Flotation uses bubble attachment to separate solids or dispersed liquids from a liquid phase.[16]

Membrane filtration

Membrane filtration has gotten a lot of attention for inorganic effluent treatment since it can remove not only suspended solids and organic components, but also inorganic pollutants such heavy metals. For heavy metal removal, several forms of

membrane filtration, such as ultrafiltration, nanofiltration, and reverse osmosis, can be used depending on the particle size that can be maintained.[17][18]

Ion exchange

Ion exchange is a reversible ion exchange process in which an insoluble substance (resin) takes ions from an electrolytic solution and releases additional ions of the same charge in a chemically comparable amount without changing the resin's structure.[19][20]

Electrochemical treatment techniques

[18]

  • Electrodialysis (ED)
  • Membrane electrolysis (ME)
  • Electrochemical precipitation (EP)

Adsorption

Adsorption is a mass transfer process in which a substance is transported from the liquid phase to the surface of a solid/liquid (adsorbent) and becomes physically and chemically bonded (adsorbate). Adsorption can be classified into two forms based on the type of attraction between the adsorbate and the adsorbent: physical and chemical adsorption, commonly known as physisorption and chemisorptions.[21][22]

Activated carbon

Activated carbons (ACs) or biological-activated carbon (BAC)[23] are effective adsorbents for a wide variety of contaminants. The adsorptive removal of color, aroma, taste, and other harmful organics and inorganics from drinking water and wastewater is one of their industrial applications.[24]

Both a high surface area and a large pore size can improve the efficiency of activated carbon. Activated carbon was utilized by a number of studies to remove heavy metals and other types of contaminants from wastewater. The cost of activated carbon is rising due to a shortage of commercial activated carbon (AC). Because of its high surface area, porosity, and flexibility, activated carbon has a lot of potential in wastewater treatment.[24]

Biological

This is the method by which dissolved and suspended organic chemical components are eliminated through

biological oxidation and biosynthesis, microorganisms can degrade organic materials in wastewater. Microorganisms involved in wastewater treatment produce end products such as minerals, carbon dioxide, and ammonia during the biological oxidation process. The minerals (products) remained in the wastewater and were discharged with the effluent. Microorganisms use organic materials in wastewater to generate new microbial cells with dense biomass that is eliminated by sedimentation throughout the biosynthesis process.[26]

Standards

Main article: Drinking water quality standards

Many developed countries specify standards to be applied in their own country. In Europe, this includes the

Ministry of Environmental Protection in 2002.[29]

Where drinking water quality standards do exist, most are expressed as guidelines or targets rather than requirements, and very few water standards have any legal basis or, are subject to enforcement.[30] Two exceptions are the European Drinking Water Directive and the Safe Drinking Water Act in the United States, which require legal compliance with specific standards.

Developing countries

Further information: Self-supply of water and sanitation

Reverse Osmosis Water Purification Units (ROWPU) are portable, self-contained water treatment plants are becoming more available for public use.[33]

For waterborne disease reduction to last, water treatment programs that research and development groups start in

developing countries
must be sustainable by the citizens of those countries. This can ensure the efficiency of such programs after the departure of the research team, as monitoring is difficult because of the remoteness of many locations.

Energy Consumption: Water treatment plants can be significant consumers of energy. In California, more than 4% of the state's electricity consumption goes towards transporting moderate quality water over long distances, treating that water to a high standard.[34] In areas with high quality water sources which flow by gravity to the point of consumption, costs will be much lower. Much of the energy requirements are in pumping. Processes that avoid the need for pumping tend to have overall low energy demands. Those water treatment technologies that have very low energy requirements including

slow sand filters, gravity aqueducts
.

A 2021 study found that a large-scale water chlorination program in urban areas of Mexico massively reduced childhood diarrheal disease mortality rates.[35]

Materials

Stainless steels, such as Type 304L and 316L, are used extensively in the fabrication of water treatment plants due to their corrosion resistance to water and to the corrosivity of chlorination used for disinfection.[36][37]

See also

References

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  2. ^ "Linda Lawton – 11th International Conference on Toxic Cyanobacteria". Retrieved 2021-06-25.
  3. ^ "Chlorine". Drinking water inspectorate. Retrieved 2 March 2023.
  4. ^ "wastewater treatment | Process, History, Importance, Systems, & Technologies". Encyclopedia Britannica. October 29, 2020. Retrieved 2020-11-04.
  5. ISBN 0-07-112250-8
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  6. S2CID 259296091
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  7. ^ "PM to open South Asia's largest single STP in Dhaka on Thursday". www.dhakatribune.com. 2023-07-12. Retrieved 2023-07-14.
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  9. ISSN 1226-086X
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  16. ISBN 978-1-58829-165-3
    , retrieved 2021-11-12
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  18. ^
    ISSN 1385-8947
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  19. ISBN 978-1-58829-165-3
    , retrieved 2021-11-12
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    PMID 22459012
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  26. ISBN 978-1-315-27610-6
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  27. ^ "Legislation: The Directive overview". Environment. Brussels: European Commission. 2019-12-31.
  28. ^ Guidelines for Drinking-water Quality, Fourth Edition; World Health Organization; 2011
  29. ^ "Environmental quality standards for surface water".
  30. ^ What is the purpose of drinking water quality guidelines/regulations?. Canada: Safe Drinking Water Foundation. Pdf. Archived 2011-10-06 at the Wayback Machine
  31. ^ "Household Water Treatment Guide". Centre for Affordable Water and Sanitation Technology, Canada. March 2008.
  32. ^ "Sand as a low-cost support for titanium dioxide photocatalysts". Materials Views. Wiley VCH.
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  34. ^ "Energy Costs of Water in California". large.stanford.edu. Retrieved 2017-05-07.
  35. S2CID 236955246
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  36. ^ R.E. Avery, S. Lamb, C.A. Powell and A.H. Tuthill. "Stainless Steels for Potable Water Treatment Plants". Nickel Institute.{{cite web}}: CS1 maint: multiple names: authors list (link)
  37. ^ A.H. Tuthill and S. Lamb. "Guidelines for the use of Stainless Steel in Municipal Waste Water Treatment Plants". Nickel Institute.

External links

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