 | |
      |
| |
| |
| Chemical Problems |
 TOTAL DISSOLVED SOLIDS (T.D.S.)
EPA Maximum Contaminant level: 100~200 mg/L |
Source : Pure water is a good conductor of electricity, true or false? The answer might surprise you. Pure water is a very poor conductor of electricity, in fact, it is highly resistant to electrical impulses. It's the other stuff in the water that make it a good conductor of electricity, and the more stuff, the better conductor of electricity water is. The primary inorganic ions that make up TDS is Calcium Ca++, Magnesium Mg++, Sodium Na+, Iron Fe++, Manganese Mn++, Bicarbonate HCO3-, Chloride Cl-, Sulfate SO4--, Nitrate NO3-, Carbonate CO3--.the best way to eliminate these wide varieties of total dissolved solids.
Treatment : TDS reduction is accomplished by reducing the total amount in the water. This is done during the process of deionization or with Reverse Osmosis. Electro dialysis will also Reduce the TDS.nant list. |
| HARDNESS |
Source : 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 CO2 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 (CaCl2) - Reacts in boiler water to produce a low pH as follows: CaCl2 + 2HOH ==> Ca(OH)2 + 2HCl Magnesium Sulfate (MgSO4) - Commonly known as epsom salts, may have laxative effect if great enough quantity is in the water.
- Magnesium Chloride (MgCl2) - 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 : The Sterling Water Conditioner utilizes electro-kinetic technology which causes the minerals in the water to repel one another, keeping them in solution reducing the effects of hard water.
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 can not 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. |
| CHLORIDE
EPA Maximum Contaminant level: 250 mg/L |
Source : 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/l. Sea water contains over 30,000 mg/l as NaCl. 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 which 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/l which is due strictly to the objectionable salty taste produced in drinking water.
Treatment : Reverse Osmosis will remove 90 - 95% of the chlorides because of it's salt rejection capabilities . Electro dialysis and distillation are two more processes which 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.
|
| CHLORINE |
Source : 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 5-1/4% 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 has 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 : 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. |
| PH
EPA Maximum Contaminant level: <6.5, >8.5 |
Source : 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 0 and 14. Acidic [ 0 ]=========[ 7 ]==========[ 14 ] Alkaline 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 sulfuric or hydrochloric acid.
Treatment : 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. Downflow 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. Upflow neutralizers don't experience the problem of "cementing" of the bed. |
| IRON |
Source : Iron occurs naturally in ground waters in three forms, Ferrous Iron (clear water 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 material which surround them. These bacteria grow in stringy clumps and are found in most iron bearing waters.
Treatment : 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. |
| SULFATE |
Source : ulfate (SO4) occurs in almost all natural water. Most sulfate compounds originate from the oxidation of sulfite ores, the presence of shales, and the existence of industrial wastes. Sulfate is one of the major dissolved constituents in rain. High concentrations of sulfate in drinking water causes a laxative effect when combined with calcium and magnesium, the two most common components of hardness. Bacteria which attack and reduce sulfates, causes hydrogen sulfide gas (H2S) to form. Sulfate has a suggested level of 250 mg/l in the Secondary Drinking Water Standards published by the US EPA.
Treatment : Reverse Osmosis will reduce the sulfate content by 97 - 98%. Sulfates can also be reduced with a strong base anion exchanger, which is normally the last half of a two-column deionizer. |
| MAGNESIUM |
Source : 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.
Magnesium may be reduced to less than 1 mg/l with the use of a softener or cation exchanger in hydrogen form. Also see "Hardness". |
| MANGANESE |
Source : Manganese (Mn+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/l. 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/l 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. High levels 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.
MRemoval 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. |
| NITRITE |
Source : Nitrites are not usually found in drinking water supplies at concentrations above 1 or 2 mg/l (ppm). Nitrates are reduced to nitrites in the saliva of the mouth and upper GI tract. This occurs to a much greater degree in infants than in adults, because of the higher alkaline conditions in their GI tract. The nitrite then oxidizes hemoglobin in the blood stream to methemoglobin, thus limiting the ability of the blood to carry oxygen throughout the body. Anoxia (an insufficiency of oxygen) and death can occur. The US EPA has established the MCL (maximum contaminant level) for nitrite at 1 mg/l.
MNitrites are removed in the same manner as nitrates; Reverse Osmosis, anion exchange, or distillation. See Nitrate - Treatment. |
| SILICA |
Source : 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/l. 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 feed water. Silica evaporates in a boiler at high temperatures and then redeposit 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.
Silica can be removed by the anion exchange portion of the demineralization process. Reverse Osmosis will reject 85 - 90% of the silica content in the water. |
|
|
|
