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WATER

 

Methods of Treatment for Water Contaminants

Acidic Water

Source of Acidic Water

Acidic waters usually attain their acidity from the seepage of acid mine waters, or acidic industrial wastes. Acid mine waters are frequently too low in pH to provide suitable drinking water even after neutralization and treatment.

Treatment of Acidic Water

Acidic water can be corrected by injecting soda ash or caustic soda (sodium hydroxide) into the water supply to raise the pH. Utilization of these two chemicals slightly increases the alkalinity in direct proportion to the amount used. Acidic water can also be neutralized up to a point by running it through calcite, corosex or a combination of the two. The calcite and the corosex both neutralize by dissolving and they add hardness to the water as the neutralization takes place; therefore, they both need to be replenished on a periodic basis.

Ammonia

Source of Ammonia

Ammonia (NH3) gas, usually expressed as Nitrogen, is extremely soluble in water. It is the natural product of decay of organic nitrogen compounds. Ammonia finds its way to surface supplies from the runoff in agricultural areas where it is applied as fertilizer. It can also find its way to underground aquifers from animal feed lots. Ammonia is oxidized to nitrate by bacterial action. A concentration of 0.1 to 1.0 ppm is typically found in most surface water supplies, and is expressed as N. Ammonia is not usually found in well water supplies because the bacteria in the soil converts it nitrates. The concentration of Ammonia is not restricted by drinking water standards. Since Ammonia is corrosive to copper alloys it is a concern in cooling systems and in boiler feed.

Treatment of Ammonia

Ammonia can be destroyed chemically by chlorination. The initial reaction forms chloramine, and must be completely broken down before there is a chlorine residual. The chlorine will destroy organic contaminants in the waste stream before it will react with the ammonia. Ammonia can also be removed by cation exchange resin in the hydrogen form, which is the utilization of acid as a regenerant. Degasification will also remove Ammonia.

Arsenic

Source of Arsenic

Arsenic (As) is not easily dissolved in water, therefore, if it is found in a water supply, it usually comes from mining or metallurgical operations or from runoff from agricultural areas where materials containing arsenic were used as industrial poisons. Arsenic and phosphate easily substitute for one another chemically; therefore, commercial grade phosphate can have some arsenic in it. Arsenic is highly toxic and has been classified by the US EPA as a carcinogen. The current MCL for arsenic is 0.05 mg/l, which was derived from toxicity considerations rather than carcinogenicity.

Treatment of Arsenic

If in an inorganic form, arsenic can be removed or reduced by conventional water treatment processes. There are five ways to remove inorganic contaminants; reverse osmosis, activated alumina, ion exchange, activated carbon, and distillation. Filtration through activated carbon will reduce the amount of arsenic in drinking water from 40 – 70%. Anion exchange can reduce it by 90 – 100%. Reverse Osmosis has a 90% removal rate, and Distillation will remove 98%. If the arsenic is present in organic form, it can be removed by oxidation of the organic material and subsequent coagulation.

Bacteria

Source of Bacteria

Bacteria are tiny organisms occurring naturally in water. Not all types of bacteria are harmful. Many organisms found in water are of no health concern since they do not cause disease. Biological contamination may be separated into two groups: (1) pathogenic (disease causing) and (2) non-pathogenic (not disease causing). Pathogenic bacteria cause illnesses such as typhoid fever, dysentery, gastroenteritis, infectious hepatitis, and cholera. All water supplies should be tested for biological content prior to use and consumption. E.Coli (Escherichia Coli) is the coliform bacterial organism that is looked for when testing the water. This organism is found in the intestines and fecal matter of humans and animals. If E.Coli is found in a water supply along with high nitrate and chloride levels, it usually indicates that waste has contaminated the supply from a septic system or sewage dumping, and has entered by way of runoff, a fractured well casing, or broken lines. If coliform bacteria are present, it is an indication that disease-causing bacteria may also be present. Four or fewer colonies / 100 ml of coliforms, in the absence of high nitrates and chlorides, implies that surface water is entering the water system. If pathogenic bacteria is suspected, a sample of water should be submitted to the Board of Health or US EPA for bacteriological testing and recommendations. The most common non-pathogenic bacteria found in water is iron bacteria. Iron bacteria can be readily identified by the red, feathery floc that forms overnight at the bottom of a sample bottle containing iron and iron bacteria.

Treatment of Bacteria

Bacteria can be treated by microfiltration, reverse osmosis, ultrafiltration, or chemical oxidation and disinfection. Ultraviolet sterilization will also kill bacteria; but turbidity, color, and organic impurities interfere with the transmission of ultraviolet energy and may decrease the disinfection efficiency below levels to insure destruction. Ultraviolet treatment also does not provide residual bactericidal action; therefore, periodic flushing and disinfection must be done. Ultraviolet sterilization is usually followed by 0.2-micron filtration when dealing with high purity water systems. The most common and undisputed method of bacteria destruction is chemical oxidation and disinfection. Ozone injection into a water supply is one form of chemical oxidation and disinfection. A residual of 0.4 mg/i must be established and a retention time of four minutes is required. Chlorine injection is the most widely recognized method of chemical oxidation and disinfection. Chlorine must be fed at 3 to 5 ppm to treat for bacteria and a residual of 0.4 ppm of free chlorine must be maintained for 30 minutes in order to meet Isi standards. Reverse Osmosis will remove over 99% of the bacteria in a drinking water system.

Calcium

Source of Calcium

Calcium is the major component of hardness in water and is usually in the range of 5 – 500 mg/i, as CaCO3. Calcium is derived from nearly all rock, but the greatest concentrations come from limestone and gypsum. Calcium ions are the principal cations in most natural waters. Calcium reduction is required in treating cooling tower makeup. Complete removal is required in metal finishing, textile operations, and boiler feed applications.

Treatment of Calcium

Calcium, as with all hardness, can be removed with a simple sodium form cation exchanger (softener). Reverse Osmosis will remove 95% – 98% of the calcium in the water. Electrodialysis and Ultrafiltration also will remove calcium. Calcium can also be removed with the hydrogen form cation exchanger portion of a deionizer system.

Carbon Dioxide

Source of Carbon Dioxide

Free carbon dioxide (C02) exists in varying amounts in most natural water supplies. Most well waters will contain less than 50 ppm. Carbon Dioxide in water yields an acidic condition. Water (H2O) plus carbon dioxide (C02) yields carbonic acid (H2C03). The dissociation of carbonic acid yields hydrogen (H) and bicarbonate alkalinity (HCO3). The pH value will drop as the concentration of carbon dioxide increases, and conversely1will increase as the bicarbonate alkalinity content increases.

H20 + CO2 <===> H2CO3 <==> H+ + HCO3

Water with a pH of 3.5 or below generally, contains mineral acids such as sulfuric or hydrochloric acid. Carbon Dioxide can exist in waters with pH values from 3.6 to 8.4, but will never be present in waters having a pH of 8.5 or above. The pH value is not a measurement of the amount of carbon dioxide in the water, but rather the relationship of carbon dioxide and bicarbonate alkalinity.

Treatment of Carbon Dioxide

Free CO2 can be easily dissipated by aeration. A two-column deionizer (consisting of a hydrogen form strong acid cation and a hydroxide form strong base anion) will also remove the carbon dioxide. The cation exchanger adds the hydrogen ion (H+), which shifts the above equation to the left in favor of water and carbon dioxide release. The anion resin removes the carbon dioxide by actually removing the bicarbonate ion. A forced draft degasifier placed between the cation and anion will serve to blow off the CO2 before it reaches the anion bed, thus reducing the capacity requirements for the anion resin. The CO2 can be eliminated by raising the pH to 8.5 or above with a soda ash or caustic soda chemical feed system.

Chlorine

Source of Chlorine

Chlorine is the most commonly used agent for the disinfection of water supplies. Chlorine is a strong oxidizing agent capable of reacting with many impurities in water including ammonia, proteins, amino acids, iron, and manganese. The amount of chlorine required to react with these substances is called the chlorine demand. Liquid chlorine is sodium hypochlorite. Household liquid bleach is 5% sodium hypochlorite. Chlorine in the form of a solid is calcium hypochlorite. When chlorine is added to water, a variety of chloro-compounds are formed. An example of this would be when ammonia is present, inorganic compounds known as chloramines are produced. Chlorine also reacts with residual organic material to produce potentially carcinogenic compounds, the Trihalomethanes (THM’s): chloroform, bromodichloromethane, bromoform, and chlorodibromomethane. THM regulations have required that other oxidants and disinfectants be considered in order to minimize THM formation. The other chemical oxidants being examined are: potassium permanganate, hydrogen peroxide, chloramines, chlorine dioxide, and ozone. No matter what form of chlorine is added to water, hypochlorite, hypochlorous acid, and molecular chlorine will be formed, the reaction lowers the pH, thus making the water more corrosive and aggressive to steel and copper pipe.

Treatment of Chlorine

Chlorinated water can be dosed with sulfite-bisulfite-sulfur dioxide or passed through a activated carbon filter. Activated carbon will remove 880,000 ppm of free chlorine per cubic foot of media.

Chromium

Source of Chromium

Chromium is found in drinking water as a result of industrial waste contamination. The occurrence of excess chromium is relatively infrequent. Proper tests must be run on the water supply to determine the form of the chromium present. Trivalent chromium (Cr-3) is slightly soluble in water, and is considered essential in man and animals for efficient lipid, glucose, and protein metabolism. Hexavalent chromium (Cr-6) on the other hand is considered toxic. The US EPA classifies chromium as a human carcinogen. The current Drinking Water Standards MCL is .005 mg/I.

Treatment of Chromium

Trivalent chromium (Cr-3)can be removed with strong acid cation resin regenerated with hydrochloric acid. Hexavalent chromium (Cr-6) on the other hand requires the utilization of a strong base anion exchanger that must be regenerated with caustic soda (sodium hydroxide) NaOH. Reverse Osmosis can effectively reduce both forms of chromium by 90 to 97%. Distillation will also reduce chromium.

Color

Source of Color

Color in water is almost always due to organic material, which is usually extracted from decaying vegetation. Color is common in surface water supplies, while it is virtually non-existent in spring water and deep wells. Color in water may also be the result of natural metallic ions (iron and manganese). A yellow tint to the water indicates that humic acids are present, referred to as “tannins”. A reddish color would indicate the presence of precipitated iron. Stains on bathroom fixtures and on laundry are often associated with color also. Reddish-brown is ferric hydroxide (iron) will precipitate when the water is exposed to air. Dark brown to black stains are created by manganese. Excess copper can create blue stains.

Treatment of Color

Color is removed by chemical feed, retention and filtration. Activated carbon filtration will work most effectively to remove color in general. Anion scavenger resin will remove tannins, but must be preceded by a softener or mixed with fine mesh softener resin. See the headings Iron, Manganese, and Copper for information their removal or reduction.

Copper

Source of Copper

Copper (Cu-3) in drinking water can be derived from rock weathering, however the principal sources are the corrosion of brass and copper piping and the addition of copper salts when treating water supplies for algae control. The body for proper nutrition requires copper. Insufficient amounts of copper lead to iron deficiency. However, high doses of copper can cause liver damage or anemia. The taste threshold for copper in drinking water is 2 – 5 mg/l. The US EPA has proposed a maximum contaminant level (MCL) of 1.3 mg/l for copper.

Treatment of Copper

Copper can be reduced or removed with sodium form strong acid cation resin (softener) dependent on the concentration. If the cation resin is regenerated with acid performance will be enhanced. Reverse osmosis or electrodialysis will remove 97 – 98% of the copper in the water supply. Activated carbon filtration will also remove copper by adsorption.

Fluoride

Source of Fluoride

Fluoride (F+) is a common constituent of many minerals. Municipal water treatment plants commonly add fluoride to the water for prevention of tooth decay, and maintain a level of 1.5 – 2.5 mg/l. Concentrations above 5 mg/l are detrimental to tooth structure. High concentrations are contained in waste water from the manufacture of glass and steel, as well as from foundry operations. Organic fluorine is present in vegetables, fruits, and nuts. Inorganic fluorine, under the name of sodium fluoride, is a waste product of aluminum and is used in some rat poisons. The MCL established for drinking water by the US EPA is 4 mg/l.

Treatment of Fluoride

Fluoride can be reduced by anion exchange. Adsorption by calcium phosphate, magnesiumiydroxide or activated carbon will also reduce the fluoride content of drinking water. Reverse osmosis will remove 93 – 95% of the fluoride.

Hardness

Source of Hardness

Hard water is found over 80% of the United States. The hardness of a water supply is determined by the content of calcium and magnesium salts. Calcium and magnesium combine with bicarbonates, sulfates, chlorides, and nitrates to form these salts. The standard domestic measurement for hardness is grains per gallon (gpg) as CaCO3. Water having a hardness content less than 0.6 gpg is considered commercially soft. The calcium and magnesium salts, which form hardness, are divided into two categories: 1) Temporary Hardness (containing carbonates), and 2) Permanent Hardness (containing non-carbonates). Below find listings of the various combinations of permanent and temporary hardness along with their chemical formula and some information on each.

Temporary Hardness Salts

 

  1. Calcium Carbonate (CaCO3) – Known as limestone, rare in water supplies. Causes alkalinity in water.

  2. Calcium Bicarbonate [Ca (HCO3) 2] – Forms when water containing CO2 comes in contact with limestone. Also causes alkalinity in water. When heated CO. is released and the calcium bicarbonate reverts back to calcium carbonate thus forming scale.

  3. Magnesium Carbonate (MgCO3) – Known as magnesite with properties similar to calcium carbonate.

  4. Magnesium Bicarbonate [Mg (HCO3)2] – Similar to calcium bicarbonate in its properties.

Permanent Hardness Salts

 

  1. Calcium Sulfate (CaSO4) – Know as gypsum, used to make plaster of paris. Will precipitate and form scale in boilers when concentrated.

  2. Calcium Chloride (CaCI2) – Reacts in boiler water to produce a low pH as follows: CaC1, + 2HOH ==> Ca(OH)2+2HC1

  3. Magnesium Sulfate (MgSO4) – Commonly known as epsom salts, may have laxative effect if great enough quantity is in the water.

  4. Magnesium Chloride (MgCI2) – Similar in properties to calcium chloride.

Sodium salts are also found in household water supplies, but they are considered harmless as long as they do not exist in large quantities. The US EPA currently has no national policy with respect to the hardness or softness of public water supplies.

Treatment of Hardness

Softeners can remove compensated hardness up to a practical limit of 100 gpg. If the hardness is above 30 gpg or the sodium to hardness ratio is greater than 33%, then economy salt settings cannot be used. If the hardness is high, then the sodium will be high after softening, and may require that reverse osmosis be used for producing drinking water.

Hydrogen Sulfide

Source of Hydrogen Sulfide

Hydrogen Sulfide (H2S) is a gas which imparts its “rotten egg” odor to water supplies. Such waters are distasteful for drinking purposes and processes in practically all industries. Most sulfur waters contain from 1 to 5 ppm of hydrogen sulfide. Hydrogen sulfide can interfere with readings obtained from water samples. It turns hardness and pH tests gray, and makes iron tests inaccurate. Chlorine bleach should be added to eliminate the H2S odor; then the hardness, pH and iron tests can be done. Hydrogen sulfide can not be tested in a lab, it must be done in the field. Hydrogen sulfide is corrosive to plumbing fixtures even at low concentrations. H2S fumes will blacken or darken painted surfaces, giving them a “smoked” appearance.

Treatment of Hydrogen Sulfide

H2S requires chlorine to be fed in sufficient quantities to eliminate it, while leaving a residual in the water (3 ppm of chlorine is required for each ppm of hydrogen sulfide). Activated carbon filtration may then be installed to remove the excess chlorine.

Iron

Source of Iron

Iron occurs naturally in ground waters in three forms, Ferrous Iron (clear waste iron), Ferric Iron (red water iron), and Heme Iron (organic iron). Each can exist alone or in combination with the others. Ferrous iron, or clear water iron as it is sometimes called, is ferrous bicarbonate. The water is clear when drawn but when turns cloudy when it comes in contact with air. The air oxidizes the ferrous iron and converts it to ferric iron. Ferric iron, or ferric hydroxide, is visible in the water when drawn; hence the name “red water iron”. Heme iron is organically bound iron complexed with decomposed vegetation. The organic materials complexed with the iron are called tannins or lignins. These organics cause the water to have a weak tea or coffee color. Certain types of bacteria use iron as an energy source. They oxidize the iron from its ferrous state to its ferric state and deposit it in the slimy gelatinous materials that surround them. These bacteria grow in stringy clumps and are found in most iron bearing waters.

Treatment of Iron

Ferrous iron (clear water iron) can be removed with a softener provided it is less than 0.5 ppm for each grain of hardness and the pH of the water is greater than 6.8. If the ferrous iron is more than 5.0 ppm, it must be converted to ferric iron by contact with a oxidizing agent such as chlorine, before it can be removed by mechanical filtration. Ferric iron (red water iron) can simply be removed by mechanical filtration. Heme iron can be removed by an organic scavenger anion resin, or by oxidation with chlorine followed by mechanical filtration. Oxidizing agents such as chlorine will also kill iron bacteria if it is present.

Lead

Source of Lead

Lead (Pb2) found in fresh water usually indicates contamination from metallurgical wastes or from lead-containing industrial poisons. Lead in drinking water is primarily from the corrosion of the lead solder used to put together the copper piping. Lead in the body can cause serious damage to the brain, kidneys, nervous system, and red blood cells. The US EPA considers lead to be a highly toxic metal and a major health threat. The current level of lead allowable in drinking water is 0.05 mg/l.

Treatment of Lead

Lead can be reduced considerably with a water softener. Activated carbon filtration can also reduce lead to a certain extent. Reverse osmosis can remove 94 to 98% of the lead in drinking water at the point-of-use. Distillation will also remove the lead from drinking water.

Magnesium

Source of Magnesium

Magnesium (Mg+2) hardness is usually approximately 33% of the total hardness of a particular water supply. Magnesium is found in many minerals, including dolomite, magnesite, and many types of clay. It is in abundance in sea water where its’ concentration is five (5) times the amount of calcium. Magnesium carbonate is seldom a major component of in scale. However, it must be removed along with calcium where soft water is required for boiler make-up, or for process applications.

Treatment of Magnesium

Magnesium may be reduced to less than 1 mg/i with the use of a softener or purification exchanger in hydrogen form. Also see “Hardness”.

Manganese

Source of Manganese

Manganese (Mg+4, Mn+2) is present in many soils and sediments as well as in rocks whose structures have been changed by heat and pressure. It is used in the manufacture of steel to improve corrosion resistance and hardness. Manganese is considered essential to plant and animal life and can be derived from such foods as corn, spinach, and whole-wheat products. It is known to be important in building strong bones and may be beneficial to the cardiovascular system. Manganese may be found in deep well waters at concentrations as high as 2 – 3 mg/i. It is hard to treat because of the complexes it can form which are dependent on the oxidation state, pH, bicarbonate-carbonate-OH ratios, and the presence of other minerals, particularly iron. Concentrations higher than 0.05 mg/i cause manganese deposits and staining of clothing and plumbing fixtures. The stains are dark brown to black in nature. The use of chlorine bleach in the laundry will cause the stains to set. The chemistry of manganese in water is similar to that of iron. A high level of manganese in the water produces an unpleasant odor and taste. Organic materials can tie up manganese in the same manner as they do iron; therefore destruction of the organic matter is a necessary part of manganese removal.

Treatment of Manganese

Removal of manganese can be done by ion exchange (sodium form cation – softener) or chemical oxidation – retention – filtration. Removal with a water softener dictates that the pH be 6.8 or higher and is beneficial to use countercurrent regeneration with brine make-up and backwash utilizing soft water. It takes 1 ppm of oxygen to treat 1.5 ppm of manganese. Greensand filter with potassium will remove up to 10 ppm if pH is above 8.0. Birm filter with air injection will reduce manganese if pH is 8.0 to 8.5. Chemical feed (chlorine, potassium permanganate, or hydrogen peroxide) followed by 20 minutes retention and then filtered with birm, greensand, carbon, or Filter Ag will also remove the manganese.

Mercury

Source of Mercury

Mercury (Hg) is one of the least abundant elements in the earth’s crust. It exists in two forms, an inorganic salt or an organic compound (methyl mercury). Mercury detected in drinking water is of the inorganic type. Organic mercury inters the food chain through fish and comes primarily from industrial chemical manufacturing waste or from the leaching of coal ash. If inorganic mercury inters the body, it usually settles in the kidneys. Where as organic mercury attacks the central nervous system. The MCL (maximum contamination level) for mercury set by the US EPA is 0.002 mg/l.

Treatment of Mercury

Activated carbon filtration is very effective for the removal of mercury. Reverse osmosis will remove 95 – 97 00 of it.

Methane

Source of Methane

Methane (CH4), often called marsh gas, is the primary component of natural gas. It is commonly found where land fills once existed and is generated from decaying of plants or other carbon based matter. It can also be found in and around oil fields. Methane is colorless, odorless, nearly invisible, highly flammable, and often found in conjunction with other gases such as hydrogen sulfide. Even though methane gas gives water a milky appearance which makes it aesthetically unpleasant, there are no known health effects.

Treatment of Methane

Aeration or degasification is the only way to eliminate the problem of methane gas. Venting the casing and/or the cap of the well will reduce the problem of methane in the water, but may not completely eliminate it. Another method is to provide an atmospheric holding tank where the methane laden water cap be vented to allow the gas to dissipate. This method may not be 100% effective either. An aerator or degasifier is the proper piece of equipment to utilize for the removal of methane. Water is introduced through the top, sometimes through spray nozzles, and a1lowed to percolate through a packing material. Air is forced in the opposite direction to the water flow. The water is then collected in the bottom of the unit and repressurized.