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Did
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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IS THE PH OF RO PERMEATE WATER LOWER THAN THE FEEDWATESR PH?
This
question is
answered when you understand the equilibrium relationship between
CO2, HCO3, and CO3. In a closed system, the relative
amount of each of dune compounds vary with pH. At lower pH levels, CO2
is the predominant species. HCO3
is the predominant species at mid pH levels, and CO3 is present at higher pH levels.
Since
RO membranes will reject dissolved ions and not reject dissolved gases,
the RO permeate and RO feed will contain roughly the same amount of CO2.
The HCO3
and CO3, however, are often reduced by
1-2 orders o£ magnitude. This upsets the CO2, HCO3,
CO3 equilibrium that was established in the feed,
In a series of equilibrium reactions, CO2 will combine with
H2O driving reactions similar to that shown below, until a
new equilibrium Is established.
CO2
+ H2O --> HCO3 + H+
To
summarize:
The
new equilibrium will always result in a lowering of permeate pH if
there is CO2 gas present in the feed water.
Usually,
the pH drop is largest for waters with high amounts of alkalinity or HCO3.
When
there is very little CO2, HCO3, or CO3, there is very little pH drop
observed in the permeate.
Therefore it is not true that reverse osmosis filters will
always reduce the pH level of water to a noticeable amount.
The pH difference after the RO depends on the composition of your input
water source; depends on whether you have large amounts of gases such
as CO2 in your local water supply. If you are concerned with
the pH of your drinking water, you should avoid guess work and get your
water tested with an accurate pH tester meter (avoid those $10 paper testing
strips, very inaccurate with pH readings). If you see that your pH is
indeed below 7 with a good amount, you can consider putting a pH increaser
filter as a final stage of your reverse osmosis system and correct acid
water problem easily.
Some
countries have regulations governing the pH of drinking water. Typically,
the pH is recommended to be in the 6.5-9.0 range. It is
our understanding that the purpose
of these pH regulations are to minimize corrosion of piping materials so that metals like lead and copper do not dissolve into the drinking water supply.
Healthy and Convenient!
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