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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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ALKALINITY OF DRINKING WATER EXPLAINED
Alkalinity
of water may be due to the presence of one or more of a number of ions.
These include hydroxides, carbonates and bicarbonates. As discussed in
previous articles, hydroxide ions are always present in water, even if
the concentration is extremely small. However, significant concentrations
of hydroxides are unusual in natural water supplies, but may be present
after certain types of treatment. Small amounts of carbonates are found
in natural water supplies in certain sections of the country, rarely exceeding
3 or 4 gpg. They may also be found in water after treatment, such as lime
soda ash softening. Bicarbonates are the most common sources of alkalinity.
Almost all natural supplies have a measurable amount of this ion, ranging
from 0 to about 50 gpg.
Alkalinity.
The alkalinity of water may be defined as its capacity to neutralize acid.
Alkali substances in water include hydroxides or bases. They can be detected
by their acrid taste and by the fact that they cause red litmus paper
to turn blue.
Phosphates
and silicates are rarely found in natural supplies in concentrations significant
in the home. Compounds containing these ions may be used in a variety
of water treatment processes. Moderate concentrations of alkalinity are
desirable in most water supplies to balance the corrosive effects of acidity.
However, excesive quantities cause a number of problems. These ions are,
of course, free in the water, but have their counterpart in cations such
as calcium, magnesium and sodium or potassium.
You probably will not
notice an alkaline condition due to bicarbonate ions except when present
in large amounts. In contrast, you should readily detect alkalinity due
even to fairly small amounts of carbonate and hydroxide ions.
Strongly
alkaline Waters have an objectionable "soda" taste. The EPA Secondary
Drinking Water Regulations limit alkalinity only in terms of total dissolved
solids (500 ppm) and to some extent by the limitation on pH.
Highly mineralized
alkaline waters also cause excessive drying of the skin due to the fact
that they tend to remove normal skin oils.
Troublesome amounts
of alkalinity can be removed by reverse osmosis,
along with other total dissolved solids. Other methods of water treatment
remove total dissolved solids and alkalinity, but they are somewhat less
suitable for household use than reverse osmosis. These methods are distillation
and deionization (demineralization).
Several other methods of water treatment will remove alkalinity, but these methods
are not satisfactory for household use. They include:
1.
Lime
softening removes hardness. At the same time, this process will precipitate an
equivalent amount of alkalinity. Lime softening is usually restricted
to industrial and municipal installations.
Lime softening.
While reducing total alkalinity, lime softening does convert HC03– to CO3--, a stronger alkalinity ion.
2. An
anion resin regenerated with sodium chloride removes substantially all
the anions (carbonates, bicarbonates, and sulfates, as well as nitrates).
It replaces these anions with a chemically equivalent amount of chloride
ions. The disadvantage of this process is that in almost all cases a high
chloride ion concentration results. At the point of exhaustion, the resin
has the tendency to unload high concentrations of the anions it carries
including the nitrates. For household purposes, such results are almost
as undesirable as the original alkalinity.
3. The feed of a mineral
acid will neutralize the alkalinity of a water. Hydrochloric acid, sulfuric
acid or a combination of these can be used. This process converts the
bicarbonates and carbonates present into carbonic acid. At this point,
it is advisable to provide some method to permit the resulting carbon
dioxide gas to escape into the atmosphere. The disadvantages of this acid
feed technique are obvious. There are needs for precise control of the
process and caution in handling the strong acid.
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