Water treatment is any process that improves thequality ofwater to make it appropriate for a specific end-use. The end use may bedrinking, industrial water supply,irrigation, river flow maintenance, water recreation or many other uses, including being safely returned to the environment. Water treatment removescontaminants 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 andirrigation use.
Water contamination is primarily caused by the discharge of untreated wastewater from industrial and commercial activities. Theeffluent from various enterprises, which contains varying levels of contaminants, is dumped into rivers or other water resources. The wastewater may have a high proportion oforganic andinorganic contaminants at the initial discharge. Industries generate wastewater as a result of fabrication processes, processes dealing withpaper andpulp,textiles,chemicals, and from various streams such ascooling towers,boilers, and production lines.[1]
Treatment fordrinking water production involves the removal of contaminants and/or inactivation of any potentially harmful microbes from raw water to produce water that ispure enough for human consumption without any short term or long term risk of any adverse health effect. In general terms, the greatest microbial risks are associated with ingestion of water that is contaminated with human or animal (including bird) feces. Feces can be a source of pathogenic bacteria, viruses, protozoa and helminths. The removal or destruction of microbial pathogens is essential, and commonly involves the use of reactive chemical agents such assuspended solids, to removebacteria,algae,viruses,fungi, andminerals includingiron andmanganese. Research including ProfessorLinda Lawton's group atRobert Gordon University, Aberdeen is working to improve detection ofcyanobacteria.[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 fortap water or other uses, may be further treated before use, often using an in-line treatment process. Such treatments can includewater softening or ion exchange.[citation needed]
Wastewater treatment is a process which removescontaminants fromwastewater. The resultingeffluent, discharged to a water body, has an acceptable impact on the environment.[4] Domestic wastewater, also called municipal wastewater orsewage, is processed at asewage treatment plant. Industrial wastewater is often processed at a specially-designedindustrial wastewater treatment facility,[5] or at a sewage treatment plant. In the latter case the industry typically performs on-site pretreatment of the waste, before it is sent to the municipal plant. Other types of wastewater treatment plants includeagricultural wastewater treatment andleachate treatment plants.
The term "wastewater treatment" is often used to mean "sewage treatment".[6]
Common processes in wastewater treatment includephase separation, such as sedimentation, various biological and chemical processes, such as oxidation, and 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.[6]: Ch.14 Biogas can be another by-product if the process uses anaerobic treatment.
Water treatment is used to reduce impact on equipment used in 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. Steamboilers 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, andLegionnaires' 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.[citation needed]
For the elimination of hazardous chemicals from the water, manytreatment procedures have been applied.[7]
The processes involved in removing the contaminants include physical processes such assettling andfiltration,chemical processes such asdisinfection andcoagulation, and biological processes such asslow 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.
Different chemical procedures for the conversion into final products or the removal of pollutants are used for the safe disposal of contaminants.[8]
Physical techniques of water/waste water treatment rely on physical phenomena to complete the removal process, rather than biological or chemical changes.[8]
Most common physical techniques are:
Also referred to as "Conventional" Treatment
Chemical precipitation is a common process used to reduceheavy metals concentrations in wastewater. The dissolved metal ions are transformed to an insoluble phase by a chemical interaction with aprecipitant agent such as lime. In industrial applications stronger alkalis may be used to effect complete precipitation. In drinking water treatment, thecommon-ion effect is often used to help reduce water hardness.[13]
Flotation uses bubble attachment to separate solids or dispersed liquids from a liquid phase.[14]
Membrane filtration can remove suspended solids and organic components, and inorganic pollutants such heavy metals. For heavy metal removal, several forms ofmembrane filtration, such asultrafiltration,nanofiltration, andreverse osmosis, can be used depending on the particle size that can be maintained.[15][16]Antiscalants can help maintain membrane filtration.[17] Some small molecules canpermeate to some extent throughmembranes.[17]
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.[18][19]
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.[20][21]
Activated carbons (ACs) or biological-activated carbon (BAC)[22] 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.[23]
Both a high surface area and a largepore 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.[23]
This is the method by which dissolved and suspended organic chemical components are eliminated throughbiodegradation, in which an optimal amount ofmicroorganism is given to re-enact the same natural self-purification process.[24] Through two distinctbiological process, such asbiological oxidation andbiosynthesis, microorganisms can degrade organic materials in wastewater. Microorganisms involved in wastewater treatment produce end products such asminerals,carbon dioxide, andammonia during the biological oxidation process. The minerals (products) remained in the wastewater and were discharged with theeffluent.Microorganisms use organic materials in wastewater to generate new microbial cells with dense biomass that is eliminated bysedimentation throughout the biosynthesis process.[25]
Many developed countries specify standards to be applied in their own country. In Europe, this includes theEuropean Drinking Water Directive[26] and in the United States theUnited States Environmental Protection Agency (EPA) establishes standards as required by theSafe Drinking Water Act. For countries without a legislative or administrative framework for such standards, theWorld Health Organization publishes guidelines on the standards that should be achieved.[27] China adopted its own drinking water standard GB3838-2002 (Type II) enacted byMinistry of Environmental Protection in 2002.[28]
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.[29] 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.
Appropriate technology options in water treatment include both community-scale and household-scalepoint-of-use (POU) orself-supply designs.[30] Such designs may employsolar water disinfection methods, usingsolar irradiation to inactivate harmful waterborne microorganisms directly, mainly by the UV-A component of the solar spectrum, or indirectly through the presence of an oxidephotocatalyst, typically supportedTiO2 in itsanatase orrutile phases.[31] Despite progress inSODIS technology, military surplus water treatment units like theERDLator are still frequently used in developing countries. Newer military styleReverse Osmosis Water Purification Units (ROWPU) are portable, self-contained water treatment plants are becoming more available for public use.[32]
For waterborne disease reduction to last, water treatment programs that research and development groups start indeveloping 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.[33] 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 includingtrickling filters,slow sand filters, gravityaqueducts.
A 2021 study found that a large-scale water chlorination program in urban areas of Mexico massively reduced childhood diarrheal disease mortality rates.[34]
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.[35][36]
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