Water purification is the process of removing unwanted chemicals, biological contaminants, suspended solids and gases from water. The goal is to produce water that is suitable for a particular purpose. Most of the water is disinfected for human consumption (drinking water), but water purification can also be designed for a variety of other purposes, including meeting the requirements of medical, pharmacological, chemical and industrial applications. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filter or biologically active carbon; chemical processes such as flocculation and chlorination and the use of electromagnetic radiation such as ultraviolet light.
Purifying water can reduce particulate concentrations including suspended particles, parasites, bacteria, algae, viruses, fungi, as well as reducing concentrations of various solutes and particulates.
Standards for drinking water quality are usually established by the government or by international standards. These standards usually include minimum and maximum contaminant concentrations, depending on the purpose of water use.
Visual inspection can not determine whether water has the appropriate quality. Simple procedures such as boiling or using household activated carbon filters are not sufficient to treat any contaminants that may be present in water from unknown sources. Even natural springs - considered safe for all practical purposes in the nineteenth century - must now be tested before determining what type of treatment, if any, is needed. Chemical and microbiological analyzes, although expensive, are the only way to obtain the information needed to decide on the appropriate purification method.
According to a 2007 World Health Organization (WHO) report, 1.1 billion people do not have access to improved drinking water supplies, 88% of the 4 billion annual cases of diarrheal diseases are associated with unsafe water and inadequate sanitation and hygiene, while 1.8 million people die from diarrheal diseases each year. WHO estimates that 94% of cases of diarrheal diseases can be prevented through modifications to the environment, including access to safe water. Simple techniques for treating water at home, such as chlorination, filters, and solar disinfection, and storing it in a safe container can save many lives each year. Reducing deaths from waterborne diseases is a key public health goal in developing countries.
Video Water purification
Water source
- Groundwater: Water emerging from deep groundwater may have fallen as rain dozens, hundreds, or thousands of years ago. Soil and rock layers naturally filter groundwater to a high degree of clarity and often, require no additional treatment other than adding chlorine or chlorine as secondary disinfectants. Such water may appear as springs, artesian springs, or can be extracted from drill holes or wells. Groundwater in general has a very high bacteriological quality (ie, pathogenic bacteria or pathogenic protozoa usually do not exist), but water may be rich in dissolved solids, especially carbonates and calcium and magnesium sulfates. Depending on the strata through which water has flowed, other ions may also be present including chloride, and bicarbonate. There may be a requirement to reduce the iron or manganese content of this water in order to be accepted for drinking, cooking, and using the laundry. Primary disinfection may also be required. Where groundwater infiltration is practiced (a process in which river water is injected into the aquifer to store water when a lot of water is available during the drought), ground water may require additional treatment depending on applicable state and federal regulations.
- Lake plateau and reservoirs: Usually located upstream of river systems, highland reservoirs usually lie above any human habitation and may be surrounded by a protective zone to limit contamination opportunities. Bacteria and pathogen levels are usually low, but some bacteria, protozoa or algae will be present. Where the highlands are forested or peat, humic acid can dye water. Many highland sources have low pH that requires adjustment.
- Low rivers, canals and reservoirs: Low groundwater surfaces will have significant bacterial loads and may also contain algae, suspended solids and various dissolved constituents.
- The atmospheric water plant is a new technology that can provide high quality drinking water by extracting water from the air by cooling the air and thus condensing water vapor.
- Rainwater collection or fog collection that collects water from the atmosphere can be used primarily in areas with significant droughts and in fog areas even when there is little rain.
- Desalination of seawater with distillation or reverse osmosis.
- Surface Water: The freshwater body that opens into the atmosphere and is not designated as groundwater is called surface water.
Maps Water purification
Treatment
Goal
The goal of treatment is to remove unwanted constituents in the water and to make them safe for drinking or suitable for specific purposes in industrial or medical applications. Very varied techniques are available to remove contaminants such as fine solids, microorganisms and some inorganic and dissolved organic materials, or environmental persistent pharmaceutical pollutants. The choice of method will depend on the quality of treated water, the cost of the treatment process and the expected quality standards of the treated water.
The process below is commonly used in water purification installations. Some or most may not be used depending on the scale of the plant and the quality of the raw water (source).
Pretreatment
- Pumping and holding - Most water must be pumped from the source or directed to a pipe or retaining tank. To avoid adding contaminants to water, this physical infrastructure must be made of the right material and constructed so that accidental contamination does not occur.
- Filtering ( see also screen filters ) - The first step in purifying surface water is to remove large debris such as sticks, leaves, garbage and other large particles that can interfere with the next purification step. The deepest groundwater does not need to be filtered before the other purification steps. Storage
- - Water from rivers can also be stored in reservoirs by the river for periods between days and months to allow natural biological purification to take place. This is very important if treatment is done using a slow sand filter. Storage reservoirs also provide buffers against short periods of drought or to allow the water supply to be maintained during a temporary pollution incident in the source stream. Pre-Chlorination - In many incoming chlorinated water plants to minimize the growth of fouling organisms in pipe and tank work. Due to the potential adverse quality effects (see chlorine below), this has largely been discontinued.
setting pH
Pure water has a pH close to 7 (both alkaline and acid). Sea water can have a pH value that ranges from 7.5 to 8.4 (quite alkaline). Fresh water can have a very varying pH value depending on the geology of the drainage or aquifer basins and the influence of contaminant inputs (acid rain). If water is acidic (lower than 7), lime, soda ash, or sodium hydroxide may be added to increase the pH during the water purification process. The addition of lime increases the concentration of calcium ions, thereby increasing the hardness of the water. For very acidic water, imposing degasifiers can be an effective way to increase pH, by removing dissolved carbon dioxide from water. Making alkaline water helps the coagulation and flocculation process work effectively and also helps minimize the risk of lead dissolved from lead pipes and from lead solder in pipe fittings. Sufficient alkalinity also reduces water corrosion to iron pipes. Acids (carbonic acid, hydrochloric acid or sulfuric acid) may be added to alkaline water in some circumstances to lower the pH. Alkaline water (above pH 7.0) does not mean that lead or copper from the pipe system will not dissolve into the water. The water's ability to precipitate calcium carbonate to protect metal surfaces and reduce the likelihood of toxic metals dissolved in water is a function of pH, mineral content, temperature, alkalinity and calcium concentration.
Coagulation and flocculation
One of the first steps in most conventional water purification processes is the addition of chemicals to help remove suspended particles in water. Particles can be inorganic like clay and mud or organic such as algae, bacteria, viruses, protozoa and natural organic matter. Inorganic and organic particles contribute to the turbidity and color of water.
The addition of inorganic coagulants such as aluminum sulfate (or alum) or iron (III) salts such as iron (III) chloride causes several chemical and physical interactions simultaneously on and between particles. In a few seconds, the negative charge on the particles is neutralized by the inorganic coagulant. Also within seconds, the metal hydroxide deposits of iron and aluminum ions begin to form. These deposits merge into larger particles under natural processes such as Brownian motion and through induced mixing which is sometimes referred to as flocculation. The most commonly used term for amorphous metal hydroxides is "floc." Large and amorphous aluminum and iron (III) hydroxides absorb and mix particles in suspension and facilitate the removal of particles by subsequent sedimentation and filtration processes.
Aluminum hydroxide is formed in a fairly narrow pH range, typically: 5.5 to about 7.7. Iron (III) hydroxide can be formed over a larger pH range including a lower pH level than is effective for alum, typically: 5.0 to 8.5.
In the literature, there is much debate and confusion over the use of the term coagulation and flocculation - where coagulation ends and flocculation begins? In water purification plants, there is usually a high energy, fast mixed unit process (detention time in seconds) in which coagulant chemicals are added followed by flocculation basins (detention time ranges from 15 to 45 minutes) where low energy inputs change the large paddles or devices other soft mixing to improve floc formation. In fact, the coagulation and flocculation process is in progress after coagulant metal salts are added.
Organic polymers were developed in the 1960s as a coagulant aid and, in some cases, instead of the metal inorganic salt coagulant. Synthetic organic polymers are high molecular weight compounds that carry negative, positive or neutral charges. When organic polymers are added to water with particulates, high molecular weight compounds absorb onto the surface of the particles and through the interparticle bridging together with other particles to form floc. PolyDADMAC is a cationic (positively charged) organic polymer used in water purification plants.
Sedimentation
Water coming out of the flocculation pool can enter the sedimentary basin, also called clarifier or settling basin. It is a large tank with low water speed, allowing floc to settle down. The best sedimentation basin is located close to flocculation of the basin so transit between the two processes does not allow completion or floc break. The sedimentary basin can be rectangular, where water flows from end to end, or circular where the flow comes from the center out. Sedimentary sedimentary streams are usually above the weir so only a thin layer of water - furthest from the mud - comes out.
In 1904, Allen Hazen demonstrated that the efficiency of the sedimentation process is a function of the particle deposition rate, flow through the tank and the surface area of ​​the tank. Sedimentation tanks are usually designed in the range of 0.5 to 1.0 gallon per minute per square foot (or 1.25 to 2.5 meters per hour). In general, sedimentation basin efficiency is not a function of detention time or depth of the basin. Although, the depth of the basin should be sufficient so that the water flow does not interfere with the mud and the interaction of settled particles is promoted. Due to the concentration of particles in the increase in water settling near the surface of the sludge at the bottom of the tank, the settling rate may increase due to collisions and particle agglomeration. The typical detention times for sedimentation vary from 1.5 to 4 hours and the depth of the basin varies from 10 to 15 feet (3 to 4.5 meters).
Sloping leaning or tubing can be added to traditional sedimentary basins to improve particle removal performance. Slant plates and tubes drastically increase the available surface area for the particles to be removed along with the original Hazen theory. The amount of land surface occupied by sedimentary basins with slant plates or tubes can be much smaller than conventional sedimentary basins.
Sludge storage and removal
As the particles settle at the bottom of the sedimentary basin, a layer of mud is formed on the tank floor to be removed and treated. The amount of sludge produced is significant, often 3 to 5 percent of the total volume of water to be treated. The cost of mud treatment and disposal may affect the operating costs of the water treatment plant. The sedimentation basin can be equipped with a mechanical cleaning tool that continuously cleans the bottom, or the basin can be periodically removed from the service and cleaned manually.
Floc blanket clarifiers
The sedimentation subcategory is the removal of particulates by traps in the floc layers that are suspended when water is forced up. The main advantage of blanket floc clarifiers is that they occupy a smaller footprint than conventional sedimentation. The drawback is that the efficiency of particle removal can vary greatly depending on changes in water quality that affect and influencing water flow rate.
Dissolved air flotation
When the particles to be removed can not precipitate easily, the soluble air flotation (DAF) is often used. After the coagulation and flocculation process, water flows into the DAF tank where the air diffusers beneath the tank produce a smooth bubble attached to the floc that produces a floating mass of concentrated floc. The float fl oating blanket is removed from the surface and the clarified water is pulled from the bottom of the DAF tank. Water supplies highly susceptible to unicellular eyebrow algae and supply with low turbidity and high color often use DAF.
Filtration
After separating most flocs, water is filtered as the final step to remove the remaining suspended particles and unfinished flocs.
Fast sand filter
The most common filter type is a quick sand filter. Water moves vertically through the sand which often has a layer of activated carbon or anthracite coal on the sand. The top layer removes organic compounds, which contribute to taste and odor. The space between the sand particles is larger than the smallest suspended particles, so simple filtering is not enough. Most particles pass through the surface layer but are trapped in the pore space or attached to the sand particles. Effective filtration extends to the depth of the filter. The nature of this filter is the key to its operation: if the top layer of sand blocks all particles, the filter will quickly become blocked.
To clean the filter, water is quickly passed up through the filter, in contrast to the normal direction (called backflushing or backwashing) to remove unwanted or unwanted particles. Before this step, compressed air can be detonated through the bottom of the filter to break down the compacted filter media to aid the backwashing process; this is known as air polish . This contaminated water can be disposed of, along with sediments from sedimentary basins, or can be recycled by mixing with raw water entering the plant although this is often considered a bad practice because it again introduces high concentrations of bacteria into the raw water.
Some water treatment plants use pressure filters. It works on the same principle as fast gravity filters, differs in that the filter media is enclosed in steel vessels and water is forced through it under pressure.
Advantages:
- Filter out particles much smaller than paper and sand filters can.
- Filter out almost any particle larger than the specified pore size.
- They are very thin and fluid flows through them quickly.
- They are quite strong and can withstand pressure differences between those that are normally 2-5 atmospheres.
- They can be cleaned (reddened again) and reused.
Slow sand filter
Slow sand filters can be used where there is enough land and space, because water must be passed very slowly through filters. These filters rely on biological processing for their actions rather than physical screening. Filters are carefully constructed using a graded sand layer, with coarse sand, along with some gravel, at the bottom and the best sand at the top. The water channel at the base carries water treated for disinfection. Filtration depends on the development of a thin biological layer, called the zoogleal layer or Schmutzdecke, on the filter surface. An effective slow sand filter can remain in use for weeks or even months if pretreatment is well designed and produce water with very low nutritional levels that can not be achieved by physical methods of treatment. Very low levels of nutrients allow water to be delivered safely through distribution systems with very low levels of disinfectants, thereby reducing consumer irritation above the offensive level of chlorine and chlorine by-products. Slow sand filters are not washed again; they are nourished by having a layer of sand being eroded when the flow is ultimately blocked by biological growth.
A "large scale" special form of slow sand filtering is a bank filtration process, in which natural sediments at the riverbanks are used to provide the first stage of contaminant filtration. Although usually not clean enough to be used directly for drinking water, water obtained from associated extraction wells is much less problematic than river water taken directly from the main stream where bank filtration is often used.
Membrane filtration
Membrane filters are widely used to filter drinking water and dirt. For drinking water, membrane filters can remove almost any particle larger than 0.2 m - including giardia and cryptosporidium. Membrane filters are an effective form of tertiary care at the time. want to reuse water for industry, for limited domestic purposes, or before discharging water into rivers used by cities further downstream. They are widely used in industry, especially for drink preparation (including bottled water). However, no filtration can remove water-soluble substances such as phosphate, nitrate and heavy metal ions.
Removal of ions and other solutes
The ultrafiltration membrane uses a polymer membrane with chemically formed microscopic pores that can be used to filter solutes avoiding the use of coagulants. The type of membrane media determines how much pressure is required to move water and what size of micro-organisms can be filtered.
Ion Exchange: The ion exchange system uses ion exchange columns or zeolites â € <â €
Precipitative softening: Vibrant-rich water (calcium and magnesium ions) is treated with lime (calcium oxide) and/or soda-ash (sodium carbonate) to precipitate calcium carbonate out of a solution utilizing a common ion effect.
Electrodeionization: Water is passed between positive electrode and negative electrode. The ion exchange membrane only allows the positive ions to migrate from the treated water to the negative electrode and only negative ions toward the positive electrode. High purity deionized water is produced continuously, similar to ion exchange treatments. Complete removal of ions from water is possible if the right conditions are met. Water is usually pre-treated with reverse osmosis units to remove non-ionic organic contaminants, and with gas transfer membranes to remove carbon dioxide. A 99% water recovery is possible if the concentrate stream is fed to the RO inlet.
Disinfection
Disinfection is done either by filtering out harmful micro-organisms and also by adding disinfectant chemicals. Water is disinfected to kill pathogens that pass through the filter and provide residual doses of disinfectants to kill or disable potentially harmful microorganisms in storage and distribution systems. Possible pathogens include viruses, bacteria, including Salmonella, Cholera, Campylobacter and Shigella, and protozoa, including < > Giardia lamblia and cryptosporidia others. After the introduction of chemical disinfecting agents, water is usually stored in temporary storage - often called a contact tank or clean well to allow disinfectant action to be completed.
Chlorine disinfection
The most common disinfection method involves some form of chlorine or compounds such as chloramine or chlorine dioxide. Chlorine is a powerful oxidant that quickly kills many harmful microorganisms. Since chlorine is a toxic gas, there is a danger of release associated with its use. This problem is avoided by the use of sodium hypochlorite, which is a relatively inexpensive solution used in household bleaches that release free chlorine when dissolved in water. Chlorine solution can be produced on site by electrolysis of general salt solution. Solid form, calcium hypochlorite, releases chlorine when in contact with water. However, the handling of solids requires greater manual human contact through the opening of pouches and pouring than the use of gas cylinders or bleaches that are more easily automated. Generation of liquid sodium hypochlorite is both inexpensive and safer than the use of solid gas or chlorine. Chlorine levels of up to 4 milligrams per liter (4 parts per million) are considered safe in drinking water.
All forms of chlorine are widely used, regardless of their respective deficiencies. One disadvantage is that chlorine from any source reacts with natural organic compounds in the water to form harmful chemical byproducts. These by-products, trihalomethanes (THMs) and haloacetic acid (HAAs), are carcinogenic in large quantities and regulated by the United States Environmental Protection Agency (EPA) and the Water Supply Inspectorate in the United Kingdom. The formation of THM and haloacetic acid can be minimized by effectively removing organic water from water effectively before adding chlorine. Although chlorine is effective in killing bacteria, it has limited effectiveness against protozoa that form cysts in water ( Giardia lamblia and Cryptosporidium , both pathogens).
Disinfection of chlorine dioxide
Chlorine dioxide is a disinfectant that acts faster than chlorine. It is relatively rarely used, because in some circumstances it may create an excessive amount of chlorite, which is a by-product arranged to a low permitted level in the United States. Chlorine dioxide can be supplied as an aqueous solution and added to water to avoid gas handling problems; accumulation of chlorine dioxide gas can explode spontaneously.
Chloramine Disinfection
The use of chloramine is becoming more common as a disinfectant. Although chloramine is not as strong as oxidants, it provides a more durable residue than free chlorine and will not easily form THM or haloacetic acid. It is possible to convert chlorine into chloramine by adding ammonia to water after the addition of chlorine. Chlorine and ammonia react to form chloramine. Water distribution systems disinfected with chloramine may be nitrified, because ammonia is a nutrient for bacterial growth, with nitrate produced as a by-product.
Ozone disinfection
Ozone is an unstable molecule that easily releases an oxygen atom that provides a strong oxidizing agent that is toxic to most waterborne organisms. It is a very powerful broad-spectrum disinfectant widely used in Europe. This is an effective method to disable the harmful protozoa that make up the cyst. It also works well against almost all other pathogens. Ozone is made by passing oxygen through ultraviolet light or "cold" electricity discharge. To use ozone as a disinfectant, it should be made in place and added to water with bubble contact. Some of the advantages of ozone include the production of fewer harmful byproducts and the absence of taste and odor problems (compared with chlorination). Another advantage of ozone is leaving no residual disinfectant in the water. Ozone has been used in drinking water plants since 1906 where the first industrial ozonation plant was built in Nice, France. The US Food and Drug Administration has accepted ozone as safe; and it is applied as an anti-microbiological agent for the care, storage, and processing of food. However, although fewer by-products are formed by ozonization, it has been found that ozone reacts with bromide ions in water to produce suspected carcinogenic carcinogenic concentrations. Bromide can be found in the supply of clean water in sufficient concentration to produce (after ozonization) more than 10 parts per billion (ppb) of bromate - the maximum contaminant level established by USEPA.
Ultraviolet disinfection
Ultraviolet (UV) light is highly effective in inactivating cysts, in low turbidity water. The effectiveness of UV disinfection decreases as turbidity increases, due to absorption, scattering, and shadows caused by suspended solids. The main disadvantage of using UV radiation is that, like ozone treatment, leaving no residual disinfectant in the water; Therefore, it is sometimes necessary to add residual disinfectants after the primary disinfection process. This is often done through the addition of chloramines, discussed above as a primary disinfectant. When used in this way, chloramines provide an effective residual disinfectant with very few negative effects of chlorination.
More than 2 million people in 28 developing countries use Solar Disinfection for daily drinking water care.
Purification of drinking water
Drinking water purification devices and methods are available for disinfection and treatment in emergencies or in remote locations. Disinfection is the main goal, because aesthetic considerations such as taste, odor, appearance, and traces of chemical contamination do not affect the short-term safety of drinking water.
Additional maintenance options
- Water fluoridation: in many areas fluoride is added to water in order to prevent tooth decay. Fluoride is usually added after the disinfection process. In the US, fluoridation is usually done with the addition of hexafluorosilicic acid, which decomposes in water, producing fluoride ions.
- Waterproofing: This is a method to reduce the effects of hard water. In a water system subject to heating the hard salt can be stored as decomposition of bicarbonate ions creating carbonate ions that precipitate out of the solution. Water with a high concentration of hard salt can be treated with soda ash (sodium carbonate) depositing excess salt, through the effect of general ions, producing highly purity calcium carbonate. Calcined calcium carbonates are traditionally sold to toothpaste manufacturers. Several other methods of industrial and residential water treatment are claimed (without general scientific acceptance) to include the use of magnetic and/or electric fields that reduce the effects of hard water.
- Reduction of plumbosolvency: In areas with low-conductivity water (ie surface rainfall in frozen highland mountain ranges), water may be able to dissolve lead from incoming tin pipes. The addition of small amounts of phosphate ions and increased pH slightly helps in reducing plumbo-solvency by creating insoluble lead salts on the inner surface of the pipe.
- Radium Removal: Some groundwater sources contain radium, a radioactive chemical element. Typical sources include many groundwater sources north of the Illinois River in Illinois. Radium can be removed by ion exchange, or by water conditioning. Watering back or mud produced is low level radioactive waste.
- Fluoride Removal: Although fluoride is added to water in many areas, some areas of the world have excessive levels of natural fluoride in the water source. Excessive levels can be toxic or cause unwanted cosmetic effects such as dyeing of teeth. The method of reducing fluoride levels is through treatment with activated alumina and bone char filter media.
Other water purification techniques
In April 2007, Spencer, Massachusetts water supply became contaminated with excess sodium hydroxide (alkali) when the treatment equipment was not working.
Many municipalities have moved from chlorine-free to chloramine as disinfection agents. However, chloramine appears to be a corrosive agent in some water systems. Chloramine can dissolve the "protective" film inside an older service line, leading to the leaching of lead into a housing spigot. This can lead to dangerous exposure, including elevated blood lead levels. Lead is a known neurotoxin.
Water that is demineralized
Distillation removes all minerals from water, and reverse osmosis membrane methods and nanofiltration eliminate most of the minerals. This results in a demineralized water that is not considered ideal drinking water. The World Health Organization has been investigating the health effects of demineralized water since 1980. Human trials have found that demineralized water increases diuresis and electrolyte elimination, with decreased serum potassium concentration. Magnesium, calcium, and other minerals in water can help protect against nutritional deficiencies. Demineralized water can also increase the risk of toxic metals because it is easier to moisten materials from piping such as lead and cadmium, which are 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 ished at very high levels into the water. Recommendations for magnesium have been placed at a minimum of 10 mg/L with 20-30 mg/L optimally; for calcium 20 mg/L minimum and 40-80 mg/L optimal, and total water hardness (adding magnesium and calcium) 2-4 mmol/L. In water hardness above 5 mmol/L, incidence of gallstones, kidney stones, urinary stones, artrosis, and higher arthropathy have been observed. In addition, the desalination process may increase the risk of bacterial contamination.
Manufacturers of home refiners claim the opposite - that minerals in water are the cause of many diseases, and that the most beneficial minerals come from food, not water. They cited the American Medical Association as saying "The body's need for minerals is mostly met through food, not drinking water." The WHO report agrees that "drinking water, with some rare exceptions, is not a primary source of important elements for humans" and "not a major source of calcium and magnesium intake," but states that demineralized water is dangerous as well. "Additional evidence comes from animal experiments and clinical observations in some countries.The animals given zinc or magnesium in their drinking water have a higher concentration of these elements in the serum than animals given equal amounts of elements in much higher amounts high with food and provided with low mineral water to drink. "
History
The first experiment in water filtration was done in the 17th century. Sir Francis Bacon seeks to remove sea salt by passing the flow through a sand filter. Although his experiment was unsuccessful, it marked the beginning of a new interest in the field. Microscopic fathers, Antonie van Leeuwenhoek and Robert Hooke, used a newly discovered microscope to observe for the first time that tiny matter particles lying suspended in water, lay the groundwork for future understanding of water-borne pathogens.
Sand filter
The use of the first documented sand filter to purify the water supply was 1804, when Scottish, Scottish bastard John Gibb installed an experimental filter, selling undesirable surpluses to the public. This method was refined in the following two decades by engineers working for private water companies, and it culminated in the world's first publicly maintained water supply, installed by engineer James Simpson for the Chelsea Water Company in London in 1829. The installation was provided filtered water for every resident in the area, and network design was widely copied throughout the UK in the following decades.
Water treatment practices soon became mainstream and common, and the virtue of the system was made clear after the investigation of John Snow's doctor during an outbreak of 1854 Broad Street cholera. Snow is skeptical of the dominant miasma theory that states that disease is caused by dangerous "bad air". Although the germ theory of the disease has not been developed, Snow's observations make him underestimate the prevailing theory. His essay of 1855 In Cholera Communication Mode conclusively demonstrates the role of water supplies in spreading cholera epidemics in Soho, with the use of point distribution maps and statistical evidence to illustrate the relationship between water source quality and cholera cases. His data convinced the local council to disable the water pump, which immediately ended the outbreak.
The Metropolis Water Act introduces the water supply company regulations in London, including the minimum water quality standards for the first time. The law "makes provision to secure supplies to Metropolis of pure and healthy water", and requires that all water "be effectively filtered" from 31 December 1855. This is followed up by legislation for mandatory water quality inspections, including comprehensive ones. chemical analysis, in 1858. This law sets a worldwide precedent for public health interventions of the same country across Europe. The Metropolitan Channel Disposal Commission was formed at the same time, water filtration was adopted across the country, and a new water intake on the Thames River was established on top of Teddington Lock. Automatic pressure filters, where water is forced under pressure through a filtration system, were innovated in 1899 in the UK.
Water chlorination
John Snow was the first person to successfully use chlorine to disinfect the water supply in Soho that has helped spread the cholera outbreak. William Soper also used chlorinated lime to treat impurities produced by typhoid patients in 1879.
In a paper published in 1894, Moritz Traube officially proposed the addition of chloride lime (calcium hypochlorite) to water to make it "germ-free." Two other researchers confirmed the Traube findings and published their paper in 1895. Early attempts to apply water chlorination at a water treatment plant were made in 1893 in Hamburg, Germany and in 1897 the English city of Maidstone was the first to have all the water supplies being treated with chlorine.
Permanent water chlorination began in 1905, when slow sand filters were damaged and contaminated water supplies caused a serious epidemic of typhoid fever in Lincoln, England. Dr. Alexander Cruickshank Houston uses water chlorination to stem the epidemic. The installation gives a concentrated chloride solution concentrated to the water being treated. Chlorination of water supplies helped stop the epidemic and as a precautionary measure, chlorination continued until 1911 when new water supply was instituted.
The continuous use of chlorine in the United States for disinfection was done in 1908 at Boonton Reservoir (on the Rockaway River), which serves as a supply for Jersey City, New Jersey. Chlorination was achieved by additionally controlled aqueous chloride dilute solution (calcium hypochlorite) at a dose of 0.2-0.35 ppm. The treatment process was conceived by Dr. John L. Leal and a chlorination plant designed by George Warren Fuller. Over the next few years, chlorine disinfection using chalk chloride is quickly installed in drinking water systems around the world.
The drinking water purification technique using liquid liquid chlorine gas was developed by a British officer in Indian Medical Service, Vincent B. Nesfield, in 1903. According to his own notes:
It occurred to me that chlorine gas might be found satisfactory... if appropriate means can be found to use it.... The next important question is how to make a portable gas. This can be done in two ways: By melting it, and storing it in a lead-lined iron vessel, it has a jet with a very smooth capillary channel, and comes with a tap or screw cap. The faucet is turned on, and the cylinder is placed in the required amount of water. Chlorine comes out, and in ten to fifteen minutes the water is completely safe. This method will be useful on a large scale, such as for service water carts.
US Army Major Carl Rogers Darnall, Professor of Chemistry at Army Medical School, gave this first practical demonstration in 1910. Shortly thereafter, Major William JL Lyster of the Army Medical Department used a calcium hypochlorite solution in a linen bag to treat water. For decades, the Lyster method remained the standard for US ground forces in the field and in camps, implemented in the familiar Lyster Bag (also spelled Lister Bag). This work became the basis for the city's current water purification system .
See also
- List of water and sanitation supplies by country
- Microfiltration
- Organisms involved in water purification
- Portable water purification
- Water softening
- Water conservation
- Water recycling
- Water treatment
References
Further reading
External links
- The American Water Works Association
- "Water On Tap: What You Need To Know." - Consumer Guide for Drinking Water in the US (EPA)
- Disinfection of Drinking Water Emergency - Camping, Hiking, and Travel (CDC)
- Federal Regulatory Code, Title 40, Section 141 - U.S. Main National Drinking Water Regulation
Source of the article : Wikipedia
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