Lecture 8: Water treatment processes. Objective: Understand functioning of different unit processes for water treatment. Courtesy: Dr. Irene. Choice of Water Treatment Process. Choice of treatment process depends on: Quality of raw water: Water source. Period of design year. R. i d lit f t t d t (d.). Water Treatment Plants have many Figure 1 WATER TREATMENT PROCESS .. ronaldweinland.info
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It is essential that the design of any treatment process is based on a full planning to install or upgrade a water treatment process should seek expert guidance. Application of specialized water treatment processes: • Hardness treatment This lesson on water treatment focuses on the reasons for treatment, the basic pro-. A community should be consulted when choosing a water-treatment system and should . as the water temperature reaches 50 °C, the inactivation process is.
However, even in the U. Drinking water sources are subject to contamination and require appropriate treatment to remove disease-causing agents. Public drinking water systems use various methods of water treatment to provide safe drinking water for their communities. Today, the most common steps in water treatment used by community water systems mainly surface water treatment include: Figure courtesy of EPA Coagulation and Flocculation Coagulation and flocculation are often the first steps in water treatment. Chemicals with a positive charge are added to the water. The positive charge of these chemicals neutralizes the negative charge of dirt and other dissolved particles in the water.
All forms of chlorine are widely used, despite their respective drawbacks. One drawback is that chlorine from any source reacts with natural organic compounds in the water to form potentially harmful chemical by-products. The formation of THMs and haloacetic acids may be minimized by effective removal of as many organics from the water as possible prior to chlorine addition.
Although chlorine is effective in killing bacteria, it has limited effectiveness against pathogenic protozoa that form cysts in water such as Giardia lamblia and Cryptosporidium. Chlorine dioxide is a faster-acting disinfectant than elemental chlorine. It is relatively rarely used because in some circumstances it may create excessive amounts of chlorite , which is a by-product regulated to low allowable levels in the United States.
Chlorine dioxide can be supplied as an aqueous solution and added to water to avoid gas handling problems; chlorine dioxide gas accumulations may spontaneously detonate. The use of chloramine is becoming more common as a disinfectant. Although chloramine is not as strong an oxidant, it provides a longer-lasting residual than free chlorine because of its lower redox potential compared to free chlorine.
It also does not readily form THMs or haloacetic acids disinfection byproducts. It is possible to convert chlorine to chloramine by adding ammonia to the water after adding chlorine. The chlorine and ammonia react to form chloramine. Water distribution systems disinfected with chloramines may experience nitrification , as ammonia is a nutrient for bacterial growth, with nitrates being generated as a by-product. Ozone disinfection, or ozonation, Ozone is an unstable molecule which readily gives up one atom of oxygen providing a powerful oxidizing agent which is toxic to most waterborne organisms.
It is a very strong, broad spectrum disinfectant that is widely used in Europe and in a few municipalities in the United States and Canada. It is an effective method to inactivate harmful protozoa that form cysts. It also works well against almost all other pathogens. Ozone is made by passing oxygen through ultraviolet light or a "cold" electrical discharge. To use ozone as a disinfectant, it must be created on-site and added to the water by bubble contact. Some of the advantages of ozone include the production of fewer dangerous by-products and the absence of taste and odour problems in comparison to chlorination.
No residual ozone is left in the water. Ozone has been used in drinking water plants since where the first industrial ozonation plant was built in Nice , France.
The U. Food and Drug Administration has accepted ozone as being safe; and it is applied as an anti-microbiological agent for the treatment, storage, and processing of foods. However, although fewer by-products are formed by ozonation, it has been discovered that ozone reacts with bromide ions in water to produce concentrations of the suspected carcinogen bromate. Bromide can be found in fresh water supplies in sufficient concentrations to produce after ozonation more than 10 parts per billion ppb of bromate — the maximum contaminant level established by the USEPA.
Ultraviolet light UV is very effective at inactivating cysts, in low turbidity water. UV light's disinfection effectiveness decreases as turbidity increases, a result of the absorption , scattering , and shadowing caused by the suspended solids.
The main disadvantage to the use of UV radiation is that, like ozone treatment, it leaves no residual disinfectant in the water; therefore, it is sometimes necessary to add a residual disinfectant after the primary disinfection process.
This is often done through the addition of chloramines, discussed above as a primary disinfectant. When used in this manner, chloramines provide an effective residual disinfectant with very few of the negative effects of chlorination.
Over 2 million people in 28 developing countries use Solar Disinfection for daily drinking water treatment.
Like UV, ionizing radiation X-rays, gamma rays, and electron beams has been used to sterilize water. Bromine and iodine can also be used as disinfectants. However, chlorine in water is over three times more effective as a disinfectant against Escherichia coli than an equivalent concentration of bromine , and over six times more effective than an equivalent concentration of iodine. Potable water purification devices and methods are available for disinfection and treatment in emergencies or in remote locations.
Disinfection is the primary goal, since aesthetic considerations such as taste, odour, appearance, and trace chemical contamination do not affect the short-term safety of drinking water. Other popular methods for purifying water, especially for local private supplies are listed below. In some countries some of these methods are also used for large scale municipal supplies. Particularly important are distillation de-salination of seawater and reverse osmosis.
In April, , the water supply of Spencer, Massachusetts became contaminated with excess sodium hydroxide lye when its treatment equipment malfunctioned. Many municipalities have moved from free chlorine to chloramine as a disinfection agent. However, chloramine appears to be a corrosive agent in some water systems. Chloramine can dissolve the "protective" film inside older service lines, leading to the leaching of lead into residential spigots. This can result in harmful exposure, including elevated blood lead levels.
Lead is a known neurotoxin. Distillation removes all minerals from water, and the membrane methods of reverse osmosis and nanofiltration remove most to all minerals. This results in demineralized water which is not considered ideal drinking water. The World Health Organization has investigated the health effects of demineralized water since Magnesium , calcium , and other minerals in water can help to protect against nutritional deficiency. Demineralized water may also increase the risk from toxic metals because it more readily leaches materials from piping like lead and cadmium, which is prevented by dissolved minerals such as calcium and magnesium.
Low-mineral water has been implicated in specific cases of lead poisoning in infants, when lead from pipes leached at especially high rates into the water. Manufacturers of home water distillers claim the opposite—that minerals in water are the cause of many diseases, and that most beneficial minerals come from food, not water. The first experiments into water filtration were made in the 17th century. Sir Francis Bacon attempted to desalinate sea water by passing the flow through a sand filter.
Although his experiment did not succeed, it marked the beginning of a new interest in the field. The fathers of microscopy , Antonie van Leeuwenhoek and Robert Hooke , used the newly invented microscope to observe for the first time small material particles that lay suspended in the water, laying the groundwork for the future understanding of waterborne pathogens. The first documented use of sand filters to purify the water supply dates to , when the owner of a bleachery in Paisley, Scotland , John Gibb, installed an experimental filter, selling his unwanted surplus to the public.
The practice of water treatment soon became mainstream and common, and the virtues of the system were made starkly apparent after the investigations of the physician John Snow during the Broad Street cholera outbreak. Snow was sceptical of the then-dominant miasma theory that stated that diseases were caused by noxious "bad airs". Although the germ theory of disease had not yet been developed, Snow's observations led him to discount the prevailing theory.
His essay On the Mode of Communication of Cholera conclusively demonstrated the role of the water supply in spreading the cholera epidemic in Soho ,   with the use of a dot distribution map and statistical proof to illustrate the connection between the quality of the water source and cholera cases. His data convinced the local council to disable the water pump, which promptly ended the outbreak.
The Metropolis Water Act introduced the regulation of the water supply companies in London , including minimum standards of water quality for the first time.
The Act "made provision for securing the supply to the Metropolis of pure and wholesome water", and required that all water be "effectually filtered" from 31 December This legislation set a worldwide precedent for similar state public health interventions across Europe. The Metropolitan Commission of Sewers was formed at the same time, water filtration was adopted throughout the country, and new water intakes on the Thames were established above Teddington Lock.
Automatic pressure filters, where the water is forced under pressure through the filtration system, were innovated in in England. John Snow was the first to successfully use chlorine to disinfect the water supply in Soho that had helped spread the cholera outbreak. William Soper also used chlorinated lime to treat the sewage produced by typhoid patients in In a paper published in , Moritz Traube formally proposed the addition of chloride of lime calcium hypochlorite to water to render it "germ-free.
Permanent water chlorination began in , when a faulty slow sand filter and a contaminated water supply led to a serious typhoid fever epidemic in Lincoln, England. Alexander Cruickshank Houston used chlorination of the water to stem the epidemic. His installation fed a concentrated solution of chloride of lime to the water being treated.
The chlorination of the water supply helped stop the epidemic and as a precaution, the chlorination was continued until when a new water supply was instituted. The first continuous use of chlorine in the United States for disinfection took place in at Boonton Reservoir on the Rockaway River , which served as the supply for Jersey City, New Jersey.
The treatment process was conceived by Dr. John L. Leal and the chlorination plant was designed by George Warren Fuller. The technique of purification of drinking water by use of compressed liquefied chlorine gas was developed by a British officer in the Indian Medical Service , Vincent B. Nesfield, in According to his own account:. It occurred to me that chlorine gas might be found satisfactory The next important question was how to render the gas portable. This might be accomplished in two ways: By liquefying it, and storing it in lead-lined iron vessels, having a jet with a very fine capillary canal, and fitted with a tap or a screw cap.
The tap is turned on, and the cylinder placed in the amount of water required. The chlorine bubbles out, and in ten to fifteen minutes the water is absolutely safe. This method would be of use on a large scale, as for service water carts.
Shortly thereafter, Major William J. Lyster of the Army Medical Department used a solution of calcium hypochlorite in a linen bag to treat water. For many decades, Lyster's method remained the standard for U.
This work became the basis for present day systems of municipal water purification. From Wikipedia, the free encyclopedia. This article is about large scale, municipal water purification. For other uses, see Purification of water. Further information: Water supply. See also: Water filter.
Main article: Water chlorination. Ultraviolet germicidal irradiation. Portable water purification. The examples and perspective in this article deal primarily with the United States and do not represent a worldwide view of the subject.
You may improve this article , discuss the issue on the talk page , or create a new article , as appropriate. April Learn how and when to remove this template message. History of water supply and sanitation. Water portal Sustainable development portal. List of water supply and sanitation by country Microfiltration Organisms involved in water purification Portable water purification Water softening Water conservation Water recycling Water treatment.
World Health Organization. Part 1. Making it Happen PDF. Information Collection Rule Data Analysis. Archived from the original PDF on July 12, Retrieved 29 June American Water Works Association. Water Quality and Treatment.
New York: Water Treatment: Principles and Design. Hoboken, NJ: Cincinnati, OH. Mansoor; Davra, Komal Water Science and Technology: Water Supply.
Ion exchange materials: Retrieved 11 February Journal American Water Works Association. Center for Disease Control. Applied Microbiology. Lay summary — CDC Retrieved CS1 maint: Multiple names: Centers for Disease Control. Archived from the original PDF on Clin Infect Dis.
Retrieved 2 November Diallo May Opportunities and Challenges" PDF. Nanoparticle Res. Retrieved 24 May Jr; Wilson, Barbara H. Gu, Baohua; Coates, John D. Springer US. Nature Reviews Microbiology. Environmental Health Perspectives. Rolling revision of the WHO Guidelines for drinking-water quality.
Health risks from drinking demineralised water. Retrieved on History of Water Filters. Steps of the anaerobic digestion process . Figure 7. Major steps in anaerobic decomposition .
Suitable wastewaters include livestock manure, food processing effluents, petroleum wastes if the toxicity is controlled , and canning and dyestuff wastes where soluble organic matters are implemented in the treatment.
Most anaerobic processes solids fermentation occur in two predetermined temperature ranges: mesophilic or thermophilic. The temperature ranges are 30—38oC and 38—50oC, respectively [ 3 ]. In contrast to aerobic systems, absolute stabilization of organic matter is not achievable under anaerobic conditions. Therefore, subsequent aerobic treatment of the anaerobic effluents is usually essential. The final waste matter discharged by the anaerobic treatment includes solubilized organic matter that is acquiescent to aerobic treatment demonstrating the possibility of installing collective anaerobic and aerobic units in series [ 1 ].
Anaerobic digesters Samer [ 9 ] elucidated and illustrated the structures and constructions of the anaerobic digesters and the used building materials. Samer [ 10 ] developed an expert system for planning and designing biogas plants. Figures 8 to 13 show different types of anaerobic digesters. While Figures 1 4 and 15 show some industrial applications. Table 1 shows the advantages and disadvantages of anaerobic treatment compared to aerobic treatment. Figure 8. Figure 9.
Single-stage conventional anaerobic digester . Figure Dual-stage high rate digester . Schematic representation of digester types. Flow-through A—B and contact systems C—F . The upper scheme shows a two-stage anaerobic sludge digester, while the lower scheme shows the conventional sludge digestion plant .
Primary digestion tank with screw mixing pump and external heater . Wastewater treatment plant for corn processing industry . By definition, the anaerobic treatment is conducted without oxygen.
It is different from an anoxic process, which is a reduced environment in contrast to an environment without oxygen. Both processes are anoxic, but anaerobic is an environment beyond anoxic where the oxidation reduction potential ORP values are highly negative.
In the anaerobic process, nitrate is reduced to ammonia and nitrogen gas, and sulfate SO is reduced to hydrogen sulfide H2S. Table 1. The advantages and disadvantages of anaerobic treatment compared to aerobic treatment [ 1 ].
Anaerobic lagoons An anaerobic lagoon is a deep lagoon, fundamentally without dissolved oxygen, that enforces anaerobic conditions. The anaerobic process occurs in deep ground ponds, and such basins are implemented for anaerobic pretreatment. The anaerobic lagoons are not aerated, heated, or mixed. The depth of an anaerobic lagoon should be typically deeper than 2. Such depths diminish the amount of oxygen diffused from the surface, allowing anaerobic conditions to prevail U.
EPA, Figures 16 to 18 show different types of anaerobic lagoons. Anaerobic lagoon for strong wastewater treatment, such as meat processing wastewater .
Schematic of volume fractions in anaerobic lagoon design . Anaerobic wastewater treatment lagoon . Precisely, the bioreactor is a vessel in which a biochemical process is conducted, where it involves microorganisms e. The treatment can be conducted under either aerobic or anaerobic conditions.
The bioreactors are commonly made of stainless steel, usually cylindrical in shape and range in size from liters to cubic meters. The bioreactors are classified as batch, plug, or continuous flow reactors e. Mycoremediation is a type of bioremediation where fungi are implemented to break down the contaminants. The principal role of fungi in the ecological system is the breakdown of pollutants, which is performed by the mycelium.
The mycelium, the vegetative part of a fungus, secretes enzymes and acids that biodegrade lignin and cellulose that are the main components of vegetative fibers. Lignin and cellulose are organic compounds composed of long chains of carbon and hydrogen, and therefore they are structurally similar to several organic pollutants.
One key issue is specifying the right fungus to break down a determined pollutant. Similarly, mycofiltration is a process that uses fungal mycelia to filter toxic compounds from wastewater. In an experiment, wastewater contaminated with diesel oil was inoculated with mycelia of oyster mushrooms. The natural microbial community participates with the fungi to break down contaminants, eventually into CO2 and H2O.
Wood-degrading fungi are particularly effective in breaking down aromatic pollutants toxic components of petroleum , as well as chlorinated compounds certain persistent pesticides.
Figures 19 to 22 show different types and designs of bioreactors. A bioreactor for fungal degradation: trickle bed bioreactor . A bioreactor for fungal degradation: rotating disc bioreactor .