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you know?
Reverse osmosis is the finest water filtration method known. This process will
allow the removal of particles as small as ions from a solution. It is used
to purify water and remove salts and other impurities in order to improve the
color, taste or properties of the fluid. R.O. uses a membrane that is semi-permeable,
allowing the fluid that is being purified to pass through it, while rejecting
other ions and contaminants from passing.
This technology uses a process
known as crossflow to allow the r.o. membrane to continually clean itself. This
is the reason of why an r.o. element can last many years before clogging or
need replacement. This
water purification process requires a driving force to push the fluid through
the membrane, and the most common force is household water pressure or pressure
from a booster pump. The higher the pressure, the larger the driving force and
efficiency.
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HYDROGEN SULFIDE IN DRINKING WATER
Hydrogen
sulfide is a gas present in some waters. There is never any doubt as to
when it is present due to its offensive "rotten egg" odor. This
characteristic odor is sometimes apparent in concentrations below 1 mg/l.
Obnoxious as are the taste and odor of hydrogen sulfide, these are only
two of the problems it presents. Hydrogen sulfide promotes corrosion due
to its activity as a weak acid. Further, its presence in the air causes
silver to tarnish in a matter of seconds. High concentrations of hydrogen
sulfide gas are both flammable and poisonous. While such concentrations
are rare, their presence in drinking water has been known to cause nausea,
illness, and in extreme cases, death. High concentrations of dissolved
hydrogen sulfide can also foul the bed of an ion exchange softener. Its
continued presence will lead to lower and lower capacity and may finally
necessitate replacement of the resin bed. Generally, hydrogen sulfide
occurs in concentrations of less than 10 ppm (milligrams per liter). Occasionally
the amount goes as high as 50 to 75 mg/l. Hydrogen sulfide is more common
to well waters than to surface waters supplies.
There
are several methods for removing hydrogen sulfide from water. Most of
them involve converting the gas into elemental sulfur. This insoluble
yellow powder can then be removed by filtration. Low to moderate concentrations
of hydrogen sulfide can be eliminated through use of an oxidizing filter
of the same type satisfactory for iron removal. Because the elemental
sulfur precipitate tends to clog the filter material, it is usually necessary
to replace this material from time to time.
Chemical
treatment is recommended for medium to high concentrations of hydrogen
sulfide. In such cases, solutions of household bleach or potassium permanganate
serve as satisfactory oxidizing agents. When these oxidizing agents-such
as household bleach and permanganate solution are used, a small chemical
feed pump will serve to feed the agent into the water. A ratio of 2 mg/l
chlorine per 1 mg/1 H2S is suggested as a starting dosage.
This level will normally provide a high enough chlorine residue to insure
complete oxidation of the sulfide to sulfur. The feeding rate of the chlorine
solution may be adjusted from the original settings to provide the most
efficient operation. As in the case of iron, the chlorine solution should
enter the water upstream from the mixing or storage tank to provide sufficient
contact time. A contact time of at least 20 minutes should be allowed
for complete reaction. After this contact time, the water should pass
through an activated carbon filter to remove the now insoluble sulfur
and excess chlorine
If
potassium permanganate can be used as the oxidizing agent, an iron filter
is recommended to remove the insoluble products from the water. (Theoretically,
6.2 mg/l of pure KMnO4 are necessary to oxidize 1 mg/l H2S)
However, a slight excess of permanganate, as shown by a light pink color,
should be fed to keep the filter in a "regenerated" state. In
this way it acts as a reserve to protect against any unexpected increase
in the hydrogen sulfide content of the water.
An
activated carbon filter alone will remove, race amounts of hydrogen sulfide.
In this process the carbon simply adsorbs the gas on its surface areas.
The use of an activated carbon filter can be economical when extremely
small amounts of the gas are present. Regeneration of the activated carbon
is not usually practical. Periodic replacement is necessary. With moderate
to high concentrations of hydrogen sulfide this becomes impractical from
an economic standpoint.
Some
large users of water depend on aeration to remove hydrogen sulfide from
water. Although this is the simplest basic method, it's not normally used
for household applications. It has the disadvantage of high initial cost
and incomplete removal of the gas. There has been some use of the ion
exchange process for removal of hydrogen sulfide. The ion exchange material
for this purpose is a strong base anion substance which can be regenerated
with salt or a mixture of salt and sodium bicarbonate. This technique
has the advantage of simplicity in operation. On the other hand, it offers
relatively low flow rate and an effluent water that has all chloride anions.
Healthy and Convenient!
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