Water contamination: Any impurity present in water which results in affecting the quality of water is called as contaminant. Contamination may b caused by 4 means. Physical: It usually associates with the appearance of water, its color or turbidity, temperature, taste & odor. Chemical: It is usually indicated by comparative analysis of hard & soft water in laundering. Biological: These are concerned with the quality of drinking water and related with modifying the chemical & physical properties of water. Radiological: Radiological factors are considered in those areas where there is a possibility that water may have come in contact with radioactive materials. The radioactivity is of public health concern. There are a number of contaminants some of them are listed here: Aluminium The EPA-recommended goal is less than 0.05 mg/ l .the WHO guideline is 0.2 mg/ l Aluminum is not found naturally in the elemental form, although it is one of the most abundant metals on the earth’s surface. It is found in all soils, plants, and
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Water contamination:
Any impurity present in water which results in affecting the quality of water is called as contaminant.
Contamination may b caused by 4 means. Physical:
It usually associates with the appearance of water, its color or turbidity, temperature, taste & odor.
Chemical: It is usually indicated by comparative analysis of hard & soft water in laundering.
Biological: These are concerned with the quality of drinking water and related with modifying the chemical & physical properties of water.
Radiological: Radiological factors are considered in those areas where there is a possibility that water may have come in contact with radioactive materials. The radioactivity is of public health concern.
There are a number of contaminants some of them are listed here:
Aluminium The EPA-recommended goal is less than 0.05 mg/ l .the WHO guideline is 0.2 mg/ l Aluminum is not found naturally in the elemental form, although it is one of the most abundant metals on the earth’s surface. It is found in all soils, plants, andAnimal tissues. Aluminium-containing wastes concentrate can harm shellfish and bottom life. Alum as aluminium sulphate is commonly used as a coagulant in water treatment.Arsenic The MCL for arsenic in drinking water was lowered from 0.05 mg/l to 0.01 mg/ l by the EPA in January 2001. The WHO guideline is also 0.01mg/ l. Sources of arsenic are natural rock formations industrial wastes, arsenic pesticides, fertilizers, detergent. It is also found in foods, including shellfish and tobacco.Barium Barium may be found naturally in groundwater (usually in concentrations less than 0.1 mg/ l) and in surface water receiving industrial wastes it is also found in air. It is a muscle stimulant and in large quantities may be harmful to the nervous system and heart. The fatal dose is 550 to 600 mg.The MCL is 2 mg/ l in drinking water. A WHO guideline has not been established;Benzene
This chemical is used as a solvent and degreaser of metals. It is also a major component of gasoline. Drinking water contamination generally results from leaking underground gasoline and petroleum tanks or improper waste disposal. The EPA has set the drinking water standard for benzene at 0.005 mg/ l to reduce the risk of cancer or other adverse health effects observed in humans and laboratory animals.Cadmium The federal drinking water MCL for cadmium is 0.005 mg/ l. The WHO guideline is 0.005 mg/ l. Common sources of cadmium are water mains and galvanized iron pipes, tanks, industrial wastes (electroplating), pesticides, nickel–cadmium batteries, and cadmium-plated utensils.Carbon Dioxide The only limitation on carbon dioxide is that pertaining to corrosion. It should be less than 10 mg/ l,Carbon TetrachlorideThis chemical was once a popular household cleaning fluid. It generally gets into drinking water by improper disposal. The EPA has set the drinking water standard for carbon tetrachloride at 0.005mg/l to reduce the risk of cancer or other adverse health effects observed in laboratory animals.Chromium The total chromium MCL and WHO guideline is 0.1 mg/ l in drinking water. Chromium is found in cigarettes, some foods, and industrial plating, paint, and leather tanning wastes. chromium dust can cause cancer of the lungs and kidney damage.Copper The EPA action level for copper is 1.3 mg/ l. the WHO guideline is 1.0 mg/ l. The goal is less than 0.2 mg/ l.Fluorides Fluorides are found in many ground waters as a natural constituent, ranging from a trace to 5 mg/ l or more, and in some foods. Fluorides in concentrations greater than 4 mg/ l can cause the teeth of children to become mottled and discoloured.
Allowable limit for various contaminants:
Remedy for contaminants:
• Lime soda process • Ion exchange process
Lime Soda ProcessLime–soda ash softening requires the use of lime to convert the soluble bicarbonates of calcium and magnesium (carbonate hardness) to insoluble calcium carbonate and magnesium hydroxide, which are precipitated. The soluble calcium and magnesium sulfate and chlorides (noncarbonate hardness) are converted to insoluble calcium carbonate by the addition of soda ash and lime and precipitated.
Lime softening will also remove 90 to 99 percent of the bacteria and viruses but does not remove the need for disinfection. The sodium chloride and sodium sulfate formed remain in the water.
Excess lime is needed to achieve a pH of about 10.3 to precipitate calcium carbonate, and a pH of about 11 is needed to precipitate magnesium hydroxide. Then pH adjustment is needed to control calcium carbonate precipitation
A coagulant such as aluminum sulfate (filter alum), ferrous sulfate, ferric sulfate, or sodium aluminate is usually used to coagulate and settle the compounds formed, followed by filtration to remove turbidity and color. Large volumes of sludge with high water content are produced.
Disposal may present a problem. The lime–soda ash method is not suitable for softening small quantities of water because special equipment and technical control are necessary. the process is more economical for softening moderately hard water. As water hardness increases, the lime requirement increases, which makes the zeolite process more attractive
The Process of Ion-exchange
In the context of water purification, ion-exchange is a rapid and reversible process in which impurity ions present in the water are replaced by ions released by an ion-exchange resin.The impurity ions are taken up by the resin, which must be periodically regenerated to restore it to the original ionic form.
(An ion is an atom or group of atoms with an electric charge. Positively-charged ions are called cations and are usually metals; negatively-charged ions are called anions and are usually non-metals).
Zeolites are minerals that have a micro-porous structure.They are basically hydrated alumino-silicate minerals with an "open" structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+ and others.Zeolites are the aluminosilicate members of the family of microporous solids known as "molecular sieves".
An ion exchange resin is an insoluble matrix (or support structure) normally in the form of small (1-2 mm diameter) beads.The material has highly developed structure of pores on the surface of which are sites with easily trapped and released ions. The trapping of ions takes place only with simultaneous releasing of other ions, thus the process is called ion exchange.
