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METHODS of TREATMENT
The first concern for all of us at Aqua-Pure is your safety. We sell the best filters
in the world, and we want to be certain that the filter you buy is right for your particular
filtration needs. As a rule of thumb, if smells funny or tastes funny it probably should
not be consumed until a water analysis can be done.
There are many contaminates that can get into your water, both naturally and through outdated
pipes and man’s mistreatment of the land. Most do not pose health hazards but some, such as
lead and arsenic, can be very harmful to young children and elderly people even in small amounts.
Fortunately, today’s filtration technology can trap and eliminate nearly 100% of contaminates
from your drinking and bathing water. In fact, today’s filtration technology can render cleaner,
purer home and commercial water than at any time in history.
Below, in alphabetical order, is a list of the most common water contaminates and what treatment
is necessary to eliminate it from your drinking and bathing water.
CONTAMINANT
SOURCE and METHOD of TREATMENT
ACIDIC WATER
Source - 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 -
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.
ALUMINUM
Source - Aluminum (Al+ 3)
is an abundant metal in the Earth’s surface, but its solubilty 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 Aluminum,
however the primary source of Aluminum in drinking water comes from the use of
aluminum sulfate (alum) as a coagulant in water treatment plants. The total
dietary exposure to aluminum salts averages around 20 mg/day. Aluminum 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 -
Aluminum can be removed from water by a cation exchanger but hydrochloric acid or
sulfuric acid must be used for regeneration to remove the aluminum 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 aluminum content of drinking water by 98
+ %. Distillation will reduce the aluminum content of water by 99 +
%. Electrodialysis is also very effective in the reduction of aluminum.
AMMONIA
Source - 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 -
Ammonia can be destroyed chemically by chlorination. The initial reaction forms
chloramine, and must be completely broken down before there is a chlorine
residual. The chlorine will destroy organic contaminants in the waste stream
before it will react with the ammonia. Ammonia can also be removed by cation
exchange resin in the hydrogen form, which is the utilization of acid as a
regenerant. Degasification will also remove Ammonia.
ARSENIC
Source - 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 -
If in an inorganic form, arsenic can be removed or reduced by conventional
water treatment processes. There are five ways to remove inorganic
contaminants; reverse osmosis, activated alumina, ion exchange, activated
carbon, and distillation. Filtration through activated carbon will reduce the
amount of arsenic in drinking water from 40 - 70%. Anion exchange can reduce it
by 90 - 100%. Reverse Osmosis has a 90% removal rate, and Distillation will
remove 98%. If the arsenic is present in organic form, it can be removed by
oxidation of the organic material and subsequent coagulation.
BACTERIA
Source - Bacteria are tiny organisms occurring naturally in water.
Not all types of bacteria are harmful. Many organisms found in water are of no
health concern since they do not cause disease. Biological contamination may be
separated into two groups: (1) pathogenic (disease causing) and (2)
non-pathogenic (not disease causing). Pathogenic bacteria cause illnesses such
as typhoid fever, dysentery, gastroenteritis, infectious hepatitis, and
cholera. All water supplies should be tested for biological content prior to
use and consumption. E.Coli (Escherichia Coli) is the coliform bacterial
organism that is looked for when testing the water. This organism is found in
the intestines and fecal matter of humans and animals. If E.Coli is found in a
water supply along with high nitrate and chloride levels, it usually indicates
that waste has contaminated the supply from a septic system or sewage dumping,
and has entered by way of runoff, a fractured well casing, or broken lines. If
coliform bacteria are present, it is an indication that disease-causing
bacteria may also be present. Four or fewer colonies / 100 ml of coliforms, in
the absence of high nitrates and chlorides, implies that surface water is
entering the water system. If pathogenic bacteria is suspected, a sample of
water should be submitted to the Board of Health or US EPA for bacteriological
testing and recommendations. The most common non-pathogenic bacteria found in
water is iron bacteria. Iron bacteria can be readily identified by the red,
feathery floc that forms overnight at the bottom of a sample bottle containing
iron and iron bacteria.
Treatment -
Bacteria can be treated by microfiltration, reverse osmosis, ultrafiltration, or
chemical oxidation and disinfection. Ultraviolet sterilization will also kill
bacteria; but turbidity, color, and organic impurities interfere with the
transmission of ultraviolet energy and may decrease the disinfection efficiency
below levels to insure destruction. Ultraviolet treatment also does not provide
residual bactericidal action; therefore, periodic flushing and disinfection
must be done. Ultraviolet sterilization is usually followed by 0.2-micron
filtration when dealing with high purity water systems. The most common and
undisputed method of bacteria destruction is chemical oxidation and
disinfection. Ozone injection into a water supply is one form of chemical
oxidation and disinfection. A residual of 0.4 mg/i must be established and a
retention time of four minutes is required. Chlorine injection is the most
widely recognized method of chemical oxidation and disinfection. Chlorine must
be fed at 3 to 5 ppm to treat for bacteria and a residual of 0.4 ppm of free
chlorine must be maintained for 30 minutes in order to meet US EPA standards.
Reverse Osmosis will remove 99+ % of the bacteria in a drinking water system.
BARIUM
Source - normal'>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 - Sodiumform cation exchange units (softeners) are very effective at removing Barium.
Reverse Osmosis is also extremely effective in its removal, as well as
Electrodialysis.
BENZENE
Source - Benzene, a byproduct 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 - 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.
BICARBONATE
Source - 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 flavors; and in the
textile industry, it interferes with acid dying. Alkalinity is known as a
‘buffer”.
Treatment - 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 - Borate B (OH) 4 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 - 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 - 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 pharrnaceutical industry,
and occurs normally in blood in the range of 1.5 to 50 mg/I
Treatment -
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
Electrodialysis.
CADMIUM
Source - 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 - - 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. Electrodialysis will also remove the majority of
the cadmium.
CALCIUM
Source -
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 - Calcium, as with all hardness, can be removed with a simple sodium form cation
exchanger (softener). Reverse Osmosis will remove 95% - 98% of the calcium in the water. Electrodialysis and Ultrafiltration also will remove
calcium. Calcium can also be removed with the hydrogen form cation exchanger portion of a deionizer system.
CARBON DIOXIDE
Source - 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 (Hi) 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 <===> H2C03
<==> H+ + HCO3
Water with a pH of 3.5 or below generally, contains
mineral acids such as sulfuric or hydrochloric acid. Carbon Dioxide can exist
in waters with pH values from 3.6 to 8.4, but will never be present in waters
having a pH of 8.5 or above. The pH value is not a measurement of the
amount of carbon dioxide in the water, but rather the relationship of carbon
dioxide and bicarbonate alkalinity.
Treatment - Free CO2 can be easily dissipated by aeration. A two-column
deionizer (consisting of a hydrogen form strong acid cation and a hydroxide
form strong base anion) will also remove the carbon dioxide. The cation
exchanger adds the hydrogen ion (H+),
which shifts the above equation to the left in favor of water and carbon
dioxide release. The anion resin removes the carbon dioxide by actually removing
the bicarbonate ion. A forced draft degasifier placed between the cation and
anion will serve to blow off the CO2 before it reaches the anion
bed, thus reducing the capacity requirements for the anion resin. The CO2
can be eliminated by raising the pH to 8.5 or above with a
soda ash or caustic soda chemical feed system.
CARBON TETRACHLORIDE
Source - 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 - Reverse Osmosis will
remove 70 to 80% of the VOC’s in drinking water, as will ultrafiltration and
electrodialysis. 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.
CHLORIDE
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/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 - Reverse Osmosis will remove 90 - 95% of the chlorides because of its salt
rejection capabilities. Electrodialysis 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.
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 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 - Chlorinated water can be dosed with sulfite-bisulfite-sulfur dioxide
or passed through a activated carbon filter. Activated carbon will remove
880,000 ppm of free chlorine per cubic foot of media.
CHROMIUM
Source - 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 - Trivalent chromium (Cr=3)can be removed with strong acid
cation resin regenerated with hydrochloric acid. Hexavalent chromium (Cr*6)
on the other hand requires the utilization of a strong base anion exchanger
that must be regenerated with caustic soda (sodium hydroxide) NaOH. Reverse
Osmosis can effectively reduce both forms of chromium by 90 to 97%.
Distillation will also reduce chromium.
COLOR
Source - Color in water is almost always due to organic material, which is
usually extracted from decaying vegetation. Color is common in surface water
supplies, while it is virtually non-existent in spring water and deep wells.
Color in water may also be the result of natural metallic ions (iron and
manganese). A yellow tint to the water indicates that humic acids
are present, referred to as “tann ins “. A reddish color
would indicate the presence of precipitated iron. Stains on bathroom
fixtures and on laundry are often associated with color also. Reddish-brown
is ferric hydroxide (iron) will precipitate when the water is
exposed to air. Dark brown to black stains are
created by manganese. Excess copper can create blue stains.
Treatment - Color is removed by chemical feed, retention and filtration.
Activated carbon filtration will work most effectively to remove color in
general. Anion scavenger resin will remove tannins, but must be preceded by a
softener or mixed with fine mesh softener resin. See the headings Iron,
Manganese, and Copper for information their removal or reduction.
COPPER
Source - Copper (Cu=3) in drinking water can be derived from rock
weathering, however the principal sources are the corrosion of brass and copper
piping and the addition of copper salts when treating water supplies for algae
control. The body for proper nutrition requires copper. Insufficient amounts of
copper lead to iron deficiency. However, high doses of copper can cause liver
damage or anemia. The taste threshold for copper in drinking water is 2 - 5
mg/I. The US EPA has proposed a maximum contaminant level (MCL) of 1.3
mg/l for copper.
Treatment - Copper can be reduced or removed with sodium form strong acid cation resin
(softener) dependent on the concentration. If the cation resin is regenerated
with acid performance will be enhanced. Reverse osmosis or electrodialysis will
remove 97 - 98 % of the copper in the water supply. Activated carbon
filtration will also remove copper by adsorption.
CRYPTOSPORIDIUM
Source - 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 it’s sporozoites invade the cell lining of the gastrointestinal
tract. Symptoms of infection include diarrhea, cramps, nausea, and low-grade
fever.
Treatment - Filtration is the most effective treatment for protozoan cysts. Cartridge
POU filters rated at 0.5 micron are designed for this purpose.
CYANIDE
Source - 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 - Chlorine feed, retention, and filtration will break down the cyanide. Reverse
osmosis or electrodialysis will remove 90 - 95 % of it.
FLUORIDE
Source - 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 - 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 - 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 - 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.
HARDNESS
Source - 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 - Softeners can remove compensated hardness up to a practical limit of 100
gpg. If the hardness is above 30 gpg or the sodium to hardness ratio is greater
than 33%, then economy salt settings cannot be used. If the hardness is high,
then the sodium will be high after softening, and may require that reverse
osmosis be used for producing drinking water.
HYDROGEN SULFIDE
Source - 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 - H2S requires
chlorine to be fed in sufficient quantities to eliminate it, while leaving a
residual in the water (3 ppm of chlorine is required for each ppm of hydrogen
sulfide). Activated carbon filtration may then be installed to remove the
excess chlorine.
IRON
Source - 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 - Ferrous iron (clear water iron) can be removed with a softener provided
it is less than 0.5 ppm for each grain of hardness and the pH of the
water is greater than 6.8. If the ferrous iron is more than 5.0 ppm, it must be
converted to ferric iron by contact with a oxidizing agent such as chlorine,
before it can be removed by mechanical filtration. Ferric iron (red water iron)
can simply be removed by mechanical filtration. Heme iron can be removed by an
organic scavenger anion resin, or by oxidation with chlorine followed by
mechanical filtration. Oxidizing agents such as chlorine will also kill iron
bacteria if it is present.
LEAD
Source -
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 - 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.
LEGIONELLA
Source - In July 1976, there was an
outbreak of pneumonia effecting 221 people attending the annual Pennsylvania
American Legion convention at the Bellvue-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 honor 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
diarrhea, 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 - 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.
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.
Treatment - Magnesium may be reduced to less than 1 mg/i with the use of a softener or
purification exchanger in hydrogen form. Also see “Hardness”.
MANGANESE
Source - Manganese (Mg+4, Mn+2) is present in many soils and
sediments as well as in rocks whose structures have been changed by heat and
pressure. It is used in the manufacture of steel to improve corrosion
resistance and hardness. Manganese is considered essential to plant and animal
life and can be derived from such foods as corn, spinach, and whole-wheat
products. It is known to be important in building strong bones and may be
beneficial to the cardiovascular system. Manganese may be found in deep well
waters at concentrations as high as 2 - 3 mg/i. It is hard to treat
because of the complexes it can form which are dependent on the oxidation
state, pH, bicarbonate-carbonate-OH ratios, and the presence of other minerals,
particularly iron. Concentrations higher than 0.05 mg/i cause manganese deposits
and staining of clothing and plumbing fixtures. The stains are dark brown to
black in nature. The use of chlorine bleach in the laundry will cause the
stains to set. The chemistry of manganese in water is similar to that of iron.
A high level of manganese in the water produces an unpleasant odor and taste.
Organic materials can tie up manganese in the same manner as they do iron;
therefore destruction of the organic matter is a necessary part of manganese
removal.
Treatment - Removal of manganese can be done by ion exchange (sodium form cation -
softener) or chemical oxidation - retention - filtration.
Removal with a water softener dictates that the pH be 6.8 or higher and is
beneficial to use countercurrent regeneration with brine make-up and backwash
utilizing soft water. It takes 1 ppm of oxygen to treat 1.5 ppm of manganese.
Greensand filter with potassium will remove up to 10 ppm if pH is above 8.0.
Birm filter with air injection will reduce manganese if pH is 8.0 to 8.5.
Chemical feed (chlorine, potassium permanganate, or hydrogen peroxide)
followed by 20 minutes retention and then filtered with birm, greensand,
carbon, or Filter Ag will also remove the manganese.
MERCURY
Source - Mercury (Hg) is one of the least abundant elements in the earth’s crust. It
exists in two forms, an inorganic salt or an organic compound (methyl mercury).
Mercury detected in drinking water is of the inorganic type. Organic mercury
inters the food chain through fish and comes primarily from industrial chemical
manufacturing waste or from the leaching of coal ash. If inorganic mercury
inters the body, it usually settles in the kidneys. Where as organic mercury
attacks the central nervous system. The MCL (maximum contamination level) for
mercury set by the US EPA is 0.002 mg/l.
Treatment - Activated carbon filtration is very effective for the removal of mercury.
Reverse osmosis will remove 95 - 97 00 of it.
METHANE
Source - Methane (CH4), often called marsh gas, is the primary
component of natural gas. It is commonly found where land fills once existed
and is generated from decaying of plants or other carbon based matter. It can
also be found in and around oil fields. Methane is colorless, odorless, nearly
invisible, highly flammable, and often found in conjunction with other gases
such as hydrogen sulfide. Even though methane gas gives water a milky
appearance which makes it aesthetically unpleasant, there are no known health
effects.
Treatment - 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.
NICKEL
Source - 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 - 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.
NITRATE
Source - 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
EPA’s MCL for nitrate is 10 mg/l.
Treatment - Reverse osmosis will remove 92 - 95% of the nitrates and/or nitrites.
Anion exchange resin will also remove both as will distillation.
NITRITE
Source - Nitrites are not usually
found in drinking water supplies at concentrations above 1 or 2 mg/i (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/i.
Treatment - Nitrites are removed in the same manner as nitrates; reverse osmosis,
anion exchange, or distillation. See Nitrate - Treatment.
ODOR
Source - Taste and odor problems of many different types can be encountered in
drinking water. Troublesome compounds may result from biological growth or
industrial activities. The tastes and odors 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
odors 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”
odor caused by hydrogen sulfide. Odor 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”, “rnusty” or “spicy” odor.
Large quantities can cause the water to have a “rotten “, “septic”, “fishy”
or “medicinal” odor. Decaying vegetation is
probably the most common cause for taste and odor in surface water supplies. In
treated water supplies chlorine can react with organics and cause odor
problems. The US EPA lists odor in the Secondary Drinking Water Standards. The
contaminant effects are strictly aesthetic and a suggested Threshold Odor
Number (TON) of 3 is recommended.
Treatment - Odor 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 sulfide). Chlorine is the most common
oxidant used in water treatment, but is only partially effective on taste and
odor. Potassium permanganate and oxygen are also only partially effective.
Chloramines are not at all effective for the treatment of taste and odor. The
most effective oxidizers for treating taste and odor are chlorine dioxide and
ozone. Activated carbon has an excellent history of success in treating taste
and odor problems. The life of the carbon depends
on the presence of organics competing for sites and the concentration of the
odor-causing compound.
ORGANICS
Source - 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.
Endrin 1,1, 2-Trichloroethane
Lindane2,3,7,8-Tetrachlorodibenzodioxin (dioxin)
Methoxychlor
Vydate
Toxaphene
Simazine
2,4-D Polynuclear
aromatic hydrocarbons (PAH)
2,4,5-TP
Polychlorinated bi phenyls (PCB)
Aldicarb
Atrazine
Chlordane
Phthalates
Dalapon Acrylamide
Diquat Dibromochloropropane
(DBCP)
Endothall
1, 2-Dichloropropane
Glyphosate
Pentachlorophenol
Carbofuran
Pichloram
Alachlor -
Dinoseb
Epichlorohydrin
Ethylene dibromide (EDB)
TolueneDibromomethane
Adipates
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 - Activated carbon is generally
used to remove organics, color, and taste-and-odor 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 nanofiltration (NF) have both been proven to remove
organics. Anion exchange resin also retains organics, but periodically needs
cleaning.
PESTICIDES
Source - 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 break down
does not occur. There is no US EPA maximum contamination level (MCL) for
pesticides as a total, each substance is considered separately.
Treatment - 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.
pH
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 O and
14.
[0]==================[7]====================[14]
Acidic
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.
POTASSIUM
Source - Potassium (K+)
is an alkaline metal closely related to sodium. It is seldom that one sees it
analyzed 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 - A cation exchange resin, usually in
the form of a softener, can remove Potassium. It can also be reduced by 94 -
97% utilizing electrodialysis or reverse osmosis.
RADIUM
Source - 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 - 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.
RADON
Source - 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 - Radon is easily removed by aeration, since it is a gas. Carbon filtration is
also very effective in removing radon.
SELENTUM
Source - 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 it’s 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/I.
Treatment - Anion exchange can reduce the amount of selenium in drinking water by 60
- 95%. Reverse osmosis is excellent at reduction of selenium.
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/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 nondiffusible
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 - The anion exchange portion of the demineralization process can remove Silica.
Reverse osmosis will reject 85 - 90% of the silica content in the water.
SILVER
Source - 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-gray color 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/I under the US EPA Secondary Drinking Water
Standards.
Treatment - 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.
SOC’s
Source - 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/i
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
cis-1,
2 -Dichloroethylene 0.07
DBCP
0.0002
1,2-Dichioropropane
0.005
o-Dichlorobenzene 0.6
2,4-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
2,4,
5-TP 0.05
Toxaphene
0.005
Trans-1,2-Dichloroethylene
0.1
Xylene
10.0
Treatment - 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 nanofiltration (NF) both will
remove organics. Anion exchange resin also retains organics, but
periodically needs cleaning.
SODIUM
Source - 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 - 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.
STRONTIUM
Source - Strontium (Sr) is in the
same family as calcium and magnesium, and is one of the polyvalent earth metals
that shows 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 sulfate 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 - 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 sulfate is a membrane foulant.
SULFATE
Source - Sulfate (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/i 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.
TASTE
Source - 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 odor problems of many different
types can be encountered in drinking water. Troublesome compounds may result
from biological growth or industrial activities. The tastes and odors 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 odors 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 odor in
surface water supplies. In treated water supplies chlorine can react with
organics and cause taste and odor problems. See “ODOR” for more
information.
Treatment - Taste and odor 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 sulfide). Chlorine is the most common
oxidant used in water treatment, but is only partially effective on taste and
odor. Potassium permanganate and oxygen are also only partially effective.
Chloramines are not at all effective for the treatment of taste and odor. The
most effective oxidizers for treating taste and odor are chlorine dioxide and
ozone. Activated carbon has an excellent history of success in treating taste
and odor problems. The life of the carbon depends on the presence of organics
competing for sites and the concentration of the taste and odor-causing
compound.
TOTAL DISSOLVED SOLIDS
Source - 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 chart below indicates the TDS from various
sources.
TDS - mg/l
Distilled Water
0
Two-column Deionizer Water
8
Rain and Snow
10
Lake Michigan
170
Rivers in U.S. (average)
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 sulfate will accelerate corrosion of
metals. The US EPA has a suggested level of 500 mg/i listed in the Secondary
Drinking Water Standards.
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. Electrodiaiysis will also reduce the TDS.
THM’s
Source - THM’s (Trihalomethanes)
are produced when chlorine reacts with residual organic compounds. The four
common THM’s are trichloromethane (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 - Trihalomethanes and other halogenated organics can be reduced by adsorption
with an activated carbon filter.
TOC
Source - 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
Color - Color -
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 - Procedures and suggestions for reduction of TOC is given under the heading “ORGANICS”.
TURBIDITY
Source - 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 discoloring 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 it’s 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 - Typically turbidity can be reduced to 75 microns with a
cyclone separator, then reduced down to 20 micron with standard backwashable
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.
URANIUM
Source - 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 attacks 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 - 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.
VIRUSES
Source - Viruses are infectious organisms that range in size from 10 to 25 nanometers [1
nanometer 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 - Chemical oxidation / disinfection is 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.
VOCs
Source - 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
1,1,1-Trichloroethane 0.2
1 ,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
1,1-Dichloroethylene 0.007
trans-1,2-Dichloroethylene
0.1
cis-1,2-Dichloroethylene
0.07
Treatment - 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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