WATER TREATMENT SYSTEMS IN GRANTS PASS
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 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 in water treatment systems 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 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 (THMs): chloroform, bromodichloromethane, bromoform, and chlorodibromomethane. THM regulations have required that other oxidants and disinfectants be considered in order to minimize THIM 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.
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 Cyptosporidium
Cryptosporidium is a protozoan parasite that exists as a round oocyst 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 diarrhea, cramps, nausea, and low-grade fever.
Treatment of Cyptosporidium
Filtration is the most effective treatment for protozoan cysts. Cartridge POU filters rated at 0.5 micron are designed for this purpose.
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.
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 colorless organisms that lack a cell wall. When Giardia are ingested by humans, symptoms include diarrhea, 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 proper pretreatment 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, 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
- Calcium Carbonate (CaCO3) - Known as limestone, rare in water supplies. Causes alkalinity in water.
- 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.
- Magnesium Carbonate (MgCO3) - Known as magnesite with properties similar to calcium carbonate.
- Magnesium Bicarbonate [Mg (HCO3)2] - Similar to calcium bicarbonate in its properties.
Permanent Hardness Salts
- Calcium Sulfate (CaSO4) - Know as gypsum, used to make plaster of paris. Will precipitate and form scale in boilers when concentrated.
- Calcium Chloride (CaCI2) - Reacts in boiler water to produce a low pH as follows: CaC1, + 2HOH ==> Ca(OH)2+2HC1
- Magnesium Sulfate (MgSO4) - Commonly known as epsom salts, may have laxative effect if great enough quantity is in the water.
- 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.
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 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.
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.
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.
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 nitrate that occurs in drinking water is 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 EPAs 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.
Total Dissolved Solids
Source of Total Dissolved Solids
Total Dissolved Solids (TDS) consist mainly of carbonates, bicarbonates, chlorides, sulfates, 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 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.
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