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Treating Specific Contaminants

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.


Source of Aluminium
Aluminium (Al+3) is an abundant metal in the Earth's surface, but its solubility in water is so low that it is seldom a concern in municipal or industrial water systems. The majority of natural water contains from 0.1 ppm up to 9.0 ppm of Aluminium, however the primary source of Aluminium in drinking water comes from the use of aluminium sulphate (alum) as a coagulant in water treatment plants. The total dietary exposure to aluminium salts averages around 20 mg/day. Aluminium is on the US EPA's Secondary Drinking Water Standards list with suggested levels of 0.05 - 0.2 mg/l; dependent on case-by-case circumstances.

Treatment of Aluminium
Aluminium can be removed from water by a cation exchanger but hydrochloric acid or sulphuric acid must be used for regeneration to remove the aluminium from the resin. While this is suitable for an industrial application it is not recommended for domestic use unless it is in the form of a cation exchange tank. Reverse Osmosis will reduce the aluminium content of drinking water by over 98%. Distillation will reduce the aluminium content of water by over 99%. Electro dialysis is also very effective in the reduction of aluminium.


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.


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.


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 faecal 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, imply that surface water is entering the water system. If pathogenic bacteria are 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, colour, 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 US EPA standards. Reverse Osmosis will remove over 99% of the bacteria in a drinking water system.


Source of Barium
Barium (Ba+2) is a naturally occurring alkaline earth metal found primarily in the Midwest. Traces of the element are found in surface and ground waters. It can also be found in oil and gas drilling muds, waste from coal fired power plants, jet fuels, and automotive paints. Barium is highly toxic when its soluble salts are ingested. The current MCL for Barium is 2.0 mg/l.

Treatment of Barium
Sodiumform cation exchange units (softeners) are very effective at removing Barium. Reverse Osmosis is also extremely effective in its removal, as well as Electro dialysis.


Source of Benzene
Benzene, a by-product of petroleum refining, is used as an intermediate in the production of synthesized plastics, and is also an additive in gasoline. Gasoline contains approximately 0.8 percent benzene by volume. Benzene is classified as a volatile organic chemical (VOC) and is considered a carcinogen by the US EPA. Benzene makes its way into water supplies from leaking fuel tanks, industrial chemical waste, pharmaceutical industry waste, or from run off of pesticides. The current US EPA Ml for Benzene is 0.005 mg/l.

Treatment of Benzene
Benzene can be removed with activated carbon. Approximately 1000 gallons of water containing 570 ppb of benzene can be treated with 0.35 lbs. of activated carbon, in other words; 94,300 gallons of water can be treated for every cubic foot of carbon. The benzene must be in contact with the carbon for a minimum of 10 minutes. If the required flow rate is 5 gpm, then 50 gallon of carbon is required; which converts to approx. 7 Cu. ft. The activated carbon must be replaced when exhausted.


Source of Bicarbonate
The Bicarbonate (HCO3) ion is the principal alkaline constituent in almost all water supplies. Alkalinity in drinking water supplies seldom exceeds 300 mg/I. Bicarbonate alkalinity is introduced into the water by CO2 dissolving carbonate-containing minerals. Alkalinity control is important in boiler feed water, cooling tower water, and in the beverage industry. Alkalinity neutralizes the acidity in fruit flavours; and in the textile industry, it interferes with acid dying. Alkalinity is known as a "buffer".

Treatment of Bicarbonate
In the pH range of 5.0 to 8.0 there is a balance between excess CO2 and bicarbonate ions. Removing the free CO2 through aeration can reduce the bicarbonate alkalinity. Feeding acid to lower the pH can also reduce the alkalinity. At pH 5.0 there is only CO2 and 0 alkalinity. A strong base anion exchanger will also remove alkalinity.

Borate (Boron)

Source of Borate (Boron)
Borate B (OH4) is a compound of Boron. Most of the world's boron is contained in seawater. Sodium borate occurs in arid regions where inland seas once existed but have long since evaporated. Boron is frequently present in fresh water supplies in these same areas in the form of non-ionized boric acid. The amount of boric acid is not limited by drinking water standards, but it can be damaging to citrus crops if it is present in irrigation water and becomes concentrated in the soil.

Treatment of Borate (Boron)
Boron behaves like silica when it is in an aqueous solution. It can be removed with an Anion Exchanger or adsorbed utilizing an Activated Carbon Filter.

Bromine (Bromide)

Source of Bromine (Bromide)
Bromine is found in seawater and exists as the bromide ion at a level of about 65 mg/l. Bromine has been used in swimming pools and cooling towers for disinfection, however use in drinking water is not recommended. Ethylene bromide is used as an anti-knock additive in gasoline and methyl bromide is a soil fumigant. Bromine is extremely reactive and corrosive, and will produce irritation and burning to exposed tissues. Over 0.05 mg/1 in fresh water may indicate the presence of industrial wastes, possibly from the use of pesticides of biocides containing bromine Bromide is extensively used in the pharmaceutical industry, and occurs normally in blood in the range of 1.5 to 50 mg/l.

Treatment of Bromine (Bromide)
Reverse Osmosis will remove 93 - 96% of the bromide from drinking water. Since bromine is a disinfectant, it along with the disinfection by-products can also be removed with Activated Carbon, Ultrafiltration, or Electro dialysis.


Source of Cadmium
Cadmium enters the environment through a variety of industrial operations, it is an impurity found in zinc. By-products from mining, smelting, electroplating, pigment, and plasticizer production can contain cadmium. Cadmium emissions come from fossil fuel use. Cadmium makes its way into the water supplies as a result of deterioration of galvanized plumbing, industrial waste or fertilizer contamination. The US EPA Primary Drinking Water Standards lists Cadmium with a 0.005 mg/l MCL.

Treatment of Cadmium
Cadmium can be removed from drinking water with a sodium form cation exchanger (softener). Reverse Osmosis will remove 95 - 98% of the cadmium in the water. Electro dialysis will also remove the majority of the cadmium.


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. Electro dialysis 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 sulphuric 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 favour 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.

Carbon Tetrachloride

Source of Carbon Tetrachloride
Carbon tetrachloride (CC14) is a volatile organic chemical (VOC), and is primarily used in the manufacture of chlorofluoromethane but also in grain fumigants, fire extinguishers, solvents, and cleaning agents. Many water supplies across the country have been found to contain measurable amounts of VOC's. VOC's pose a possible health risk because a number of them are probable or known carcinogens. The detection of VOC's in a water supply indicates that a pollution incident has occurred, because these chemicals are man-made. See Volatile Organic Chemicals for a complete listing. The US EPA has classified carbon tetrachloride as a probable human carcinogen and established an MCL of 0.005 mg/l.

Treatment of Carbon Tetrachloride
Reverse Osmosis will remove 70 to 80% of the VOC's in drinking water, as will ultrafiltration and electro dialysis. Carbon tetrachloride as well as the other volatile organic chemicals (VOC's) can also be removed from drinking water with activated carbon filtration. The adsorption capacity of the carbon will vary with each type of VOC. The carbon manufacturers can run computer projections on many of these chemicals and give an estimate as to the amount of VOC which can be removed before the carbon will need replacement.


Source of Chloride
Chloride (Cl-1) is one of the major anions found in water and are generally combined with calcium, magnesium, or sodium. Since almost all chloride salts are highly soluble in water, the chloride content ranges from 10 to 100 mg/I. Sea water contains over 30,000 mg/I as NaC1. Chloride is associated with the corrosion of piping because of the compounds formed with it; for example, magnesium chloride can generate hydrochloric acid when heated. Corrosion rates and the iron dissolved into the water from piping increases as the sodium chloride content of the water is increased. The chloride ion is instrumental in breaking down passivating films that protect ferrous metals and alloys from corrosion, and is one of the main causes for the pitting corrosion of stainless steel. The SMCL (suggested maximum contaminant level) for chloride is 250 mg/I which is due strictly to the objectionable salty taste produced in drinking water.

Treatment of Chloride
Reverse Osmosis will remove 90 - 95% of the chlorides because of its salt rejection capabilities. Electro dialysis and distillation are two more processes that can be used to reduce the chloride content of water. Strong base anion exchanger which is the later portion of a two-column deionizer does an excellent job at removing chlorides for industrial applications.


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 an activated carbon filter. Activated carbon will remove 880,000 ppm of free chlorine per cubic foot of media.


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.


Source of Colour
Colour in water is almost always due to organic material, which is usually extracted from decaying vegetation. Colour is common in surface water supplies, while it is virtually non-existent in spring water and deep wells. Colour 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 colour would indicate the presence of precipitated iron. Stains on bathroom fixtures and on laundry are often associated with colour 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 Colour
Colour is removed by chemical feed, retention and filtration. Activated carbon filtration will work most effectively to remove colour 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.


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 anaemia. 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 electro dialysis will remove 97 - 98% of the copper in the water supply. Activated carbon filtration will also remove copper by adsorption


Source of Cryptosporidium
Cryptosporidium is a protozoan parasite that exists as a round 000yst about 4 to 6 microns in diameter. Oocysts pass through the stomach into the small intestine where its sporozoites invade the cell lining of the gastrointestinal tract. Symptoms of infection include diarrhoea, cramps, nausea, and low-grade fever.

Treatment of Cryptosporidium
Filtration is the most effective treatment for protozoan cysts. Cartridge POU filters rated at 0.5 micron are designed for this purpose.


Source of Cyanide
Cyanide (CN) is extremely toxic and is not commonly found at significant levels in drinking water. Cyanide is normally found in waste water from metal finishing operations. The US EPA has not classified cyanide as a carcinogen because of inadequate data. No MCL level established or even proposed.

Treatment of Cyanide
Chlorine feed, retention, and filtration will break down the cyanide. Reverse osmosis or electro dialysis will remove 90 - 95% of it.


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 aluminium 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.

Giardia Lamblia

Source of Giardia Lamblia
Giardia is a protozoan which can exist as a trophozoite, usually 9 to 21 .tm long, or as an ovoid cyst, approximately 10 um long and 6 um wide. Protozoans are unicellular and colourless organisms that lack a cell wall. When Giardia is ingested by humans, symptoms include diarrhoea, fatigue, and cramps. The US EPA has a treatment technique in effect for Giardia.

Treatment of Giardia Lamblia
Slow sand filtration or a diatomaceous earth filter can remove up to 99 % of the cysts when pre-treatment is utilized. Chemical, ultrafiltration, and reverse osmosis all effectively remove Giardia cysts. Ozone appears to be very effective against the cysts when utilized in the chemical oxidation - disinfection process instead of chlorine. The most economical and widely used method of removing Giardia is mechanical filtration. Because of the size of the parasite, it can easily be removed with precoat, solid block carbon, ceramic, pleated membrane, and spun wrapped filter cartridges.


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, sulphates, 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 Sulphate (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 Sulphate (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 Sulphide

Source of Hydrogen Sulphide
Hydrogen Sulphide (H2S) is a gas which imparts its "rotten egg" odour to water supplies. Such waters are distasteful for drinking purposes and processes in practically all industries. Most sulphur waters contain from 1 to 5 ppm of hydrogen sulphide. Hydrogen sulphide 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 odour; then the hardness, pH and iron tests can be done. Hydrogen sulphide cannot be tested in a lab; it must be done in the field. Hydrogen sulphide 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 Sulphide
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 sulphide). Activated carbon filtration may then be installed to remove the excess chlorine.


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 colour. 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 are greater than 6.8. If the ferrous iron is more than 5.0 ppm, it must be converted to ferric iron by contact with an 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.


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.


Source of Legionella
In July 1976, there was an outbreak of pneumonia effecting 221 people attending the annual Pennsylvania American Legion convention at the Bellevue-Stratford Hotel in Philadelphia. Out of the 221 people infected, 34 died. It wasn't until December 1977 that microbiologists were able to isolate a bacterium from the autopsy of the lung tissue bf one of the legionnaires. The bacterium was named "Legionella pneumophila" (Legionella in honour of the American Legion, and pneumophila which is Greek for "lung-loving") and was found to be completely different from other bacteria. Unlike patients with other pneumonias, patients with legionnaire's disease often have severe gastrointestinal symptoms, including diarrhoea, nausea, and vomiting. The US EPA has not set a MCL (maximum contamination level) for Legionella, instead it has outlined the treatment method which must be followed and the MCLG is 0 mg/l.

Treatment of Legionella
Chemical oxidation-disinfection followed by retention, then filtration could be used. Since Legionella is a bacteria, Reverse osmosis or Ultrafiltration are the preferred removal techniques.


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".


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 odour 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 counter current 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.


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. Whereas 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.


Source of Methane
Methane (CH4), often called marsh gas, is the primary component of natural gas. It is commonly found where landfills 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 colourless, odourless, nearly invisible, highly flammable, and often found in conjunction with other gases such as hydrogen sulphide. 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.


Source of Nickel
Nickel (Ni+2) is common, and exists in approximately 85% of the water supplies, and is usually around 1 ppb (part per billion). The US EPA has classified nickel as a possible human carcinogen based on inhalation exposure. Nickel has not been shown to be carcinogenic via oral exposure. No MCLG (maximum contamination level goal) has been proposed.

Treatment of Nickel
Nickel behaves the same as iron, and can be removed by a strong acid cation exchanger. Activated-carbon filtration can be used to reduce the amount of nickel in drinking water, but may not remove it all. Reverse osmosis will remove 97 - 98% of the nickel from drinking water.


Source of Nitrate
Nitrate (NO3) comes into water supplies through the nitrogen cycle rather than via dissolved minerals. It is one of the major ions in natural waters. Most nitrates that occur in drinking water are the result of contamination of ground water supplies by septic systems, feed lots, and agricultural fertilizers. Nitrate is reduced to nitrite in the body. The US EPA's MCL for nitrate is 10 mg/l.

Treatment of Nitrate
Reverse osmosis will remove 92 - 95% of the nitrates and/or nitrites. Anion exchange resin will also remove both as will distillation.


Source of Odour
Taste and odour problems of many different types can be encountered in drinking water. Troublesome compounds may result from biological growth or industrial activities. The tastes and odours may be, produced in the water supply, in the water treatment plant from reactions with treatment chemicals, in the distribution system, and/or in the plumbing of consumers. Tastes and odours can be caused by mineral contaminants in the water, such as the salty taste of water when chlorides are 500 mg/I or above, or the rotten egg odour caused by hydrogen sulphide. Odour in the drinking water is usually caused by blue-green algae. Moderate concentrations of algae in the water can cause it to have a grassy, rusty or spicy odour. Large quantities can cause the water to have a rotten, septic, fishy or medicinal odour. Decaying vegetation is probably the most common cause for taste and odour in surface water supplies. In treated water supplies chlorine can react with organics and cause odour problems. The US EPA lists odour in the Secondary Drinking Water Standards. The contaminant effects are strictly aesthetic and a suggested Threshold Odour Number (TON) of 3 is recommended.

Treatment of Odour
Odour can be removed by oxidation-reduction or by activated carbon adsorption. Aeration can be utilized if the contaminant is in the form of a gas, such as H2S (hydrogen sulphide). Chlorine is the most common oxidant used in water treatment, but is only partially effective on taste and odour. Potassium permanganate and oxygen are also only partially effective. Chloramines are not at all effective for the treatment of taste and odour. The most effective oxidizers for treating taste and odour are chlorine dioxide and ozone. Activated carbon has an excellent history of success in treating taste and odour problems. The life of the carbon depends on the presence of organics competing for sites and the concentration of the odour-causing compound.


Source of Organics
Organic matter makes up a significant part of the soil, therefore water-soluble organic compounds are present in all water supplies. Organic matter is reported on a water analysis as carbon, as it is in the TOC (total organic carbon) determination. The following is a list of organics, which regulated under the Safe Drinking Water Act of 1986.

Tetrachlorodibenzodioxin (dioxin)
Polynuclear aromatic hydrocarbons (PAH)
Polychlorinated bi phenyls (PCB)
Dibromochloropropane (DBCP)
Ethylene dibromide (EDB)
Xylene Hexachlorocyclopentadiene

Organics come from three major sources: (1) the breakdown of naturally occurring organic materials, (2) domestic and commercial chemical wastes, and (3) chemical reactions that occur during water treatment processes. The first source is comprised of humic materials, microorganisms, and petroleum-based aliphatic and aromatic hydrocarbons. Organics derived from domestic and commercial chemical wastes include wastewater discharges, agricultural runoff, urban runoff, and leaching from contaminated soils. Organic contaminants formed during water treatment include disinfection by-products such as THM's (Trihalomethanes), or undesirable components of piping assembly such as joint adhesives.

Treatment of Organics
Activated carbon is generally used to remove organics, colour, and taste-and-odour causing compounds. The contact time and service flow rate dictate the size of the carbon filter. When removing organics, restrict flow rates to 2 gpm per square foot of the filter bed. Reverse osmosis will remove 98 to 99% of the organics in the water. Ultrafiltration (TJF) and Nano filtration (NF) have both been proven to remove organics. Anion exchange resin also retains organics, but periodically needs cleaning.


Source of Pesticides
Pesticides are common synthetic organic chemicals (SOCs). Pesticides reach surface and well water supplies from the runoff in agricultural areas where they are used. Certain pesticides are banned by the government because of their toxicity to humans or their adverse effect on the environment. Pesticides usually decompose and break down as they perform their intended function. Low levels of pesticides are found where complete breakdown does not occur. There is no US EPA maximum contamination level (MCL) for pesticides as a total, each substance is considered separately.

Treatment of Pesticides
Activated carbon filtration is the most effective way to remove organics whether synthetic (like pesticides) or natural. Ultrafiltration will also remove organic compounds. Reverse osmosis will remove 97 - 99% of the pesticides.


Source of pH
The term "pH" is used to indicate acidity or alkalinity of a given solution. It is not a measure of the quantity of acid or alkali, but rather a measure of the relationship of the acid to the alkali. The pH value of a solution describes its hydrogen-ion activity. The pH scale ranges between O and 14.
Typically all natural waters fall within the range of 6.0 to 8.0 pH. A value of 7.0 is considered to be a neutral pH. Values below 7.0 are acidic and values above 7.0 are alkaline. The pH value of water will decrease as the content of CO2 increases, and will increase as the content of bicarbonate alkalinity increases. The ratio of carbon dioxide and bicarbonate alkalinity (within the range of 3.6 to 8.4) is an indication of the pH value of the water. Water with a pH value of 3.5 or below, generally contains mineral acids such as sulphuric or hydrochloric acid.

Treatment of pH
The pH can be raised by feeding sodium hydroxide (caustic soda), sodium carbonate (soda ash), sodium bicarbonate, potassium hydroxide, etc. into the water stream. A neutralizing filter containing Calcite (calcium carbonate - CaCO3) and/or Corosex (magnesium oxide -MgO) will combat low pH problems, if within the range of 5 to 6. The peak flow rate of a neutralizing filter is 6 gpm / sq. ft. down flow filters require frequent backwashing is required to prevent "cementing of the bed". A 50 -50 mix of the two seems to provide the best all-around results. Up flow neutralizers don't experience the problem of "cementing" of the bed.


Source of Potassium
Potassium (K+) is an alkaline metal closely related to sodium. It is seldom that one sees it analysed separately on a water analysis. Potassium is not a major component in public or industrial water supplies. Potassium is, however, essential in a well-balanced diet and can be found in fruits such as bananas.

Treatment of Potassium
A cation exchange resin, usually in the form of a softener, can remove Potassium. It can also be reduced by 94 - 97% utilizing electro dialysis or reverse osmosis.


Source of Radium
Radium (Rn) is a radioactive chemical element which can be found in very small amounts in pitchblende and other uranium minerals. It is used in the treatment of cancer and some skin diseases. Radium 226 and radium 228 are of most concern when found in drinking water because of the effects on the health of individuals. Radium 228 causes bone sarcomas. Radium 226 induces carcinomas in the head. Radioactivity in water can be naturally occurring or can be from man-made contamination. Radiation is generally in curies (Ci). One curie equals 3.7~x 1010 nuclear transformations per second. A picocurie (pCi) equals 10.12 curies. The US EPA has set the MCL (maximum contamination level) for radium 226 and 228 at 5 pCi/L under the NIPDWR (national interim primary drinking water regulations).

Treatment of Radium
Radium can be removed by sodium for cation exchange resin in the form of a water softener. Reverse osmosis will remove 95 - 98% of any radioactivity in the drinking water.


Source of Radon
Radon (Rn) is a radioactive gaseous chemical element formed in the atomic disintegration of radium. Radon 222 is one of the radionuclides of most concern when found in drinking water. It is a naturally occurring isotope, but can also come from man-made sources. All radionuclides are considered carcinogens, but the organs they target vary. Since radon 222 is a gas, it can be inhaled during showers or while washing dishes. There is a direct relationship between radon 222 and lung cancer. Under the NIPDWR (national interim primary drinking water regulations), the MCL (maximum contamination level) for radon 222 is set at 15 pCi/L (see radium for explanation of how radiation is measured).

Treatment of Radon
Radon is easily removed by aeration, since it is a gas. Carbon filtration is also very effective in removing radon.


Source of Selenium
Selenium (Se) is essential for human nutrition, with the majority coming from food. The concentration found in drinking water is usually low, and comes from natural minerals. Selenium is also a by-product of copper mining / smelting. It is used in photoelectric devises because its electrical conductivity varies with light. Naturally occurring selenium compounds have not been shown to be carcinogenic in animals. However, acute toxicity caused by high selenium intake has been observed in laboratory animals and in animals grazing in areas where high selenium levels exist in the soil. The US EPA has established the MCL for selenium at 0.05 mg/l.

Treatment of Selenium
Anion exchange can reduce the amount of selenium in drinking water by 60 - 95%. Reverse osmosis is excellent at reduction of selenium.


Source of Silica
Silica (SiO2) is an oxide of silicon, and is present in almost all minerals: It is found in surface and well water in the range of 1 - 100 mg/I. Silica is considered to be colloidal in nature because of the way it reacts with adsorbents. A colloid is a gelatinous substance made up of non-diffusible particles that remain suspended in a fluid medium. Silica is objectionable in cooling tower makeup and boiler feedwater. Silica evaporates in a boiler at high temperatures and then redeposits on the turbine blades. These deposits must be periodically removed or damage to the turbine will occur. Silica is not listed in the Primary or the Secondary Drinking Water Standards issued by the US EPA.

Treatment of Silica
The anion exchange portion of the demineralization process can remove Silica. Reverse osmosis will reject 85 - 90% of the silica content in the water.


Source of Silver
Silver (Ag) is a white, precious, metallic chemical element found in natural and finished water supplies. Silver oxide can be used as a disinfectant, but usually is not. Chronic exposure to silver results in a blue-grey colour of the skin and organs. This is a permanent aesthetic effect. Silver shows no evidence of carcinogenicity. Silver has a suggested level of 0.1 mg/l under the US EPA Secondary Drinking Water Standards.

Treatment of Silver
Silver can be reduced by 98% with distillation, up to 60% with activated carbon filtration, up to 90% with cation exchange or anion exchange (dependent on the pH), or up to 90% by reverse osmosis.


Source of SOC's
Over 1000 SOC's (Synthetic Organic Chemicals) have been detected in drinking water at one time or another. Most are of no concern, but some are potentially a health risk to consumers. Below is a list of synthetic organic chemicals along with the proposed MCL (maximum contamination level) in mg/I as determined by the US EPA Primary Drinking Water Regulations.

Synthetic Organic Chemicals (Proposed MCL, mg/l)

Acrylamide (0.0005)
Alachlor (0.002)
Aldicarb (0.01)
Aldicarb sulfoxide (0.01)
Aldicarb sulfone (0.04)
Atrazine (0.002)
Carbofuran (0.04)
Chlordane (0.02)
Dichloroethylene (0.07)
DBCP (0.0002)
Dichioropropane (0.005)
Dichlorobenzene (0.6)
D (0.1)
EDB (0.00005)
Epichlorohydrin (0.002)
Ethylbenzene (0.7)
Heptachlor (0.0004)
Heptachlor epoxide (0.0002)
Lindane (0.0002)
Methoxychlor (0.4)
Monochlorobenzene (0.1)
Polychlorinated biphenyls (0.0005)
Pentachlorophenol (0.2)
Styrene (0.005)
Tetrachloroethylene (0.005)
Toluene (2.0)
TP (0.05)
Toxaphene (0.005)
Dichloroethylene (0.1)
Xylene (10.0)

Treatment of SOC's
Activated carbon is generally used to remove organics. Flow rates should be restricted to 2 gpm per square foot of the filter bed. Reverse osmosis will remove 98 to 99% of the organics in the water. Ultrafiltration (U7F) and Nano filtration (NF) both will remove organics. Anion exchange resin also retains organics, but periodically needs cleaning.


Source of Sodium
Sodium (Na) is a major component in drinking water. All water supplies contain some sodium. The amount is dependent on local soil conditions. The higher the sodium content of water, the more corrosive the water becomes. A major source of sodium in natural waters is from the weathering of feldspars, evaporates and clay. The American Heart Association has recommended a maximum sodium level of 20 mg/I in drinking water for patients with hypertension or cardiovascular disease. Intake from food is generally the major source of sodium, ranging from 1100 to 3300 mg/day. Persons requiring restrictions on salt intake, usually have a sodium limitation down to 500 mg/day. The amount of sodium obtained from drinking softened water is insignificant compared to the sodium ingested in the normal human diet. The amount of sodium contained in a quart of softened, 18 grain per gallon water is equivalent to a normal slice of white bread. Sodium in the body regulates the osmotic pressure of the blood plasma to assure the proper blood volume. Sodium chloride is essential in the formation of the stomach acids necessary for the digestive processes. The US EPA sponsored a symposium which concluded that there is no relationship between soft water and cardiovascular disease. There is also no MCL published for sodium; however the US EPA suggests a level of 20 mg/l in drinking water for that portion of the population on severe sodium restricted diets of 500 mg/day or less.

Treatment of Sodium
Sodium can be removed with the hydrogen form cation exchanger portion of a deionizer. Reverse osmosis will reduce sodium by 94 - 98%. Distillation will also remove sodium.


Source of Strontium
Strontium (Sr) is in the same family as calcium and magnesium, and is one of the polyvalent earth metals that show up as hardness in the water. The presence of strontium is usually restricted to areas where there are lead ores, and its concentration in water is usually very low. Strontium sulphate is a critical reverse osmosis membrane foulant, dependent on its concentration. There is no MCL for strontium listed in the US EPA Drinking Water Standards.

Treatment of Strontium
Strontium can be removed with strong acid cation exchange resin. It can be in sodium form as in a water softener or the hydrogen form as in the cation portion of a two-column deionizer. Reverse osmosis will also reduce strontium but as stated above strontium sulphate is a membrane foul ant.


Source of Sulphate
Sulphate (SO4) occurs in almost all natural water. Most sulphate compounds originate from the oxidation of sulphite ores, the presence of shales, and the existence of industrial wastes. Sulphate is one of the major dissolved constituents in rain. High concentrations of sulphate in drinking water cause a laxative effect when combined with calcium and magnesium, the two most common components of hardness. Bacteria, which attack and reduce sulphates, causes hydrogen sulphide gas (H2S) to form. Sulphate has a suggested level of 250 mg/I in the Secondary Drinking Water Standards published by the US EPA.

Treatment of Sulphate
Reverse osmosis will reduce the sulphate content by 97 - 98%. Sulphates can also be reduced with a strong base anion exchanger, which is normally the last half of a two-column deionizer.


Source of Taste
Generally, individuals have a more acute sense of smell than taste. Taste problems in water come from total dissolved solids (TDS) and the presence of such metals as iron, copper, manganese, or zinc. Magnesium chloride and magnesium bicarbonate are significant in terms of taste. Fluoride may also cause a distinct taste. Taste and odour problems of many different types can be encountered in drinking water. Troublesome compounds may result from biological growth or industrial activities. The tastes and odours may be produced in the water supply, in the water treatment plant from reactions with treatment chemicals, in the distribution system, and/or in the plumbing of consumers. Tastes and odours can be caused by mineral contaminants in the water, such as the "salty" taste of water when chlorides are 500 mg/l or above. Decaying vegetation is probably the most common cause for taste and odour in surface water supplies. In treated water supplies chlorine can react with organics and cause taste and odour problems. See "ODOR" for more information.

Treatment of Taste
Taste and odour can be removed by oxidation-reduction or by activated carbon adsorption. Aeration can be utilized if the contaminant is in the form of a gas, such as H2S (hydrogen sulphide). Chlorine is the most common oxidant used in water treatment, but is only partially effective on taste and odour. Potassium permanganate and oxygen are also only partially effective. Chloramines are not at all effective for the treatment of taste and odour. The most effective oxidizers for treating taste and odour are chlorine dioxide and ozone. Activated carbon has an excellent history of success in treating taste and odour problems. The life of the carbon depends on the presence of organics competing for sites and the concentration of the taste and odour-causing compound.


Source of THM's
THM's (Trihalomethanes) are produced when chlorine reacts with residual organic compounds. The four common THM's are chloroform, dibromochloromethane, dichlorobromomethane, and bromoform. There have been studies that suggest a connection between chlorination by-products and particularly bladder and possibly colon and rectal cancer. An MCL of 0.10 mg/l for total THM's exists.

Treatment of THM's
Trihalomethanes and other halogenated organics can be reduced by adsorption with an activated carbon filter.


Source of TOC
TOC (Total Organic Carbon) is a measurement to track the overall organic content of water. The organic content of the water will appear on the water analysis as C (carbon). The TOC test is the most common test performed to obtain an indication of the organic content of the water. Nonspecific tests utilized to determine the organic content of water are given below:

BOD - Biochemical oxygen demand - expressed as O2
CCE - Carbon-chloroform extract - expressed in weight
CAE - Carbon-alcohol extract (performed after CCE)
COD - Chemical oxygen demand - expressed as O2
Colour - Colour - reported as APHA units
IDOD - Immediate dissolved oxygen demand - expressed as O2
LOI - Loss of ignition expressed in weight
TOC - Total organic carbon - expressed as C

The above tests are used to determine organic content of the water, for more information about different types. See "Organics".

Treatment of TOC
Procedures and suggestions for reduction of TOC is given under the heading "Organics".

Total Dissolved Solids

Source of Total Dissolved Solids
Total Dissolved Solids (TDS) consist mainly of carbonates, bicarbonates, chlorides, sulphates, phosphates, nitrates, calcium, magnesium, sodium, potassium, iron, manganese, and a few others. They do not include gases, colloids, or sediment. The TDS can be estimated by measuring the specific conductance of the water. Dissolved solids in natural waters range from less than 10 mg/I for rain to more than 100,000 mg/I for brines. Since TDS is the sum of all materials dissolved in the water, it has many different mineral sources. The chart below indicates the TDS from various sources.

Total Dissolved Solid (mg/l)
Distilled Water (0)
Two-column Deionizer Water (8)
Rain and Snow (10)
Lake Michigan (170)
Average rivers in the U.S. (210)
Missouri River (360)
Pecos River (2,600)
Oceans (35,000)
Brine Well (125,000)
Dead Sea (250,000)

High levels of total dissolved solids can adversely industrial applications requiring the use of water such as cooling tower operations; boiler feed water, food and beverage industries, and electronics manufacturers. High levels of chloride and sulphate will accelerate corrosion of metals. The US EPA has a suggested level of 500 mg/I listed in the Secondary Drinking Water Standards.

Treatment of Total Dissolved Solids
TDS reduction is accomplished by reducing the total amount in the water. This is done during the process of deionization or with reverse osmosis. Electrodiaiysis will also reduce the TDS.


Source of Turbidity
Turbidity is the term given to anything that is suspended in a water supply. It is found in most surface waters, but usually doesn't exist in ground waters except in shallow wells and springs after heavy rains. Turbidity gives the water a cloudy appearance or shows up as dirty sediment. Undissolved materials such as sand, clay, silt or suspended iron contribute to turbidity. Turbidity can cause the staining of sinks and fixtures as well as the discolouring of fabrics. Usually turbidity is measured in NTUs (nephelometric turbidity units). Typical drinking water will have a turbidity level of 0 to 1 NTU. Turbidity can also be measured in ppm (parts per million) and its size is measured in microns. Turbidity can be particles in the water consisting of finely divided solids, larger than molecules, but not visible by the naked eye; ranging in size from .001 to .150mm (1 to 150 microns). The US EPA has established an MCL for turbidity to be 0.5 to 1.0 NTU, because it interferes with disinfection of the water.

Treatment of Turbidity
Typically turbidity can be reduced to 75 microns with a cyclone separator, then reduced down to 20 micron with standard back washable filter, however flow rates of 5 gpm/ sq. ft. are recommended maximum. Turbidity can be reduced to 10 micron with a multimedia filter while providing flow rates of 15 gpm/sq. ft. Cartridge filters of various sizes are also available down into the submicron range. Ultrafiltration also reduces the turbidity levels of process water.


Source of Uranium
Uranium is a naturally occurring radionuclide. Natural uranium combines uranium 234, uranium 235, and uranium 238; however, uranium 238 makes up 99.27 percent of the composition. All radionuclides are considered carcinogens; however, the organs each attack is different. Uranium is not a proven carcinogen but accumulates in the bones similar to the way radium does. Therefore, the US EPA tends to classify it as a carcinogen. Uranium has been found to have a toxic effect on the human kidneys. Under the NIPDWR (national interim primary drinking water regulations), the MCL (maximum contamination level) for uranium is set at 15 pCi/L (see "Radium" for explanation of how radiation is measured).

Treatment of Uranium
Uranium can be reduced by both cation and anion dependent upon its state. Reverse osmosis will reduce uranium by 95 to 98%. Ultrafiltration will also reduce the amount of uranium. Activated alumina can also be utilized.


Source of Viruses
Viruses are infectious organisms that range in size from 10 to 25 nanometres [1 nanometre one billionth (10-9) of a meter]. They are particles composed of an acidic nucleus surrounded by a protein shell. Viruses depend totally on living cells and lack an independent metabolism. There are over 100 types of enteric viruses. Enteric viruses are the viruses that infect humans. Enteric viruses, which are of particular interest in drinking water, are hepatitis A, Norwalk-type viruses, rotaviruses, adenoviruses, enteroviruses, and reoviruses. The test for coliform bacterial is widely accepted as an indication whether or not the water is safe to drink; therefore tests for viruses are not usually conducted. The US EPA has established an MCL that states that 99.99% reduction or inactivation for viruses. Major enteric viruses and their diseases are shown below.

Virus (Disease)
Enteroviruses (Polio, Aseptic meningitis, and Encephalitis)
Reoviruses (Upper respiratory and gastrointestinal illness)
Rotaviruses (Gastroenteritis)
Adenoviruses (Upper respiratory and gastrointestinal illness)
Hepatitis A (Infectious)
Norwalk-type (Gastroenteritis)

Treatment of Viruses
Chemical oxidation / disinfection are the preferred treatment. Chlorine feed with 30 minute contact time for retention, followed by activated carbon filtration is the most widely used treatment. Ozone or iodine may also be utilized as oxidizing agents. Ultraviolet sterilization or distillation may also be used for the treatment of viruses.


Source of VOCs
VOCs (Volatile Organic Chemicals) pose a possible health risk because many of them are known carcinogens. Volatile organic chemicals are man-made; therefore the detection of any of them indicates that there has been a chemical spill or other incident. Volatile organic chemicals regulated under the Safe Drinking Water Act of 1986 are listed below.

Volatile Organic Chemicals (US EPA MCL-mg/l)

Trichloroethylene (0.005)
Tetrachloroethylene (0.005)
Carbon tetrachloride (0.005)
Trichloroethane (0.2)
Dichloroethane (ethylene dichloride) (0.005)
Vinyl chloride (0.002)
Methylene chloride (dichloromethane) (0.005)
Benzene (0.005)
Chlorobenzene (0.1)
Dichlorobenzene (0.6)
Trichlorobenzene (0.07)
Dichloroethylene (0.007)
Dichloroethylene (0.1)
Dichloroethylene (0.07)

Treatment of VOCs

The best choice for removal of Volatile organic chemicals is activated carbon filtration. The adsorption capacity of the carbon will vary with each type of VOC. The carbon manufacturers can run computer projections on many of these chemicals and give an estimate as to the amount of VOC that can be removed before the carbon will need replacement. Aeration may also be used alone or in conjunction with the activated carbon. Reverse osmosis will remove 70 to 80% of the VOCs in the water. Electro dialysis and ultrafiltration are also capable of reducing volatile organic chemicals.

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