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Types of Water
Filtration available
Types of water filtration include distillation, ion exchange,
deionization, carbon absorption, microporous basic filtration,
ultrafiltration, reverse osmosis, ultraviolet radiation and water
purification systems.
Probably the oldest type of water purification is distillation. In order
to distill water, it is heated to the boiling point, then the water
vapor rises to a condenser. The water cools off, thus lowering the
temperature and condensing the vapor, then it is collected and stored.
Some of the contaminants carry over into the water that has been
distilled, however, most do not. Unfortunately when boiling points are
lower than 100 degrees C, herbicides and pesticides cannot be totally
removed; in fact this process may be detrimental in that the pesticides
and herbicides may actually become concentrated in the water. Cost is a
disadvantage because energy and water in large amounts is required for
distillation. Another disadvantage is that there is a low pH with
distillation which may cause it to be acidic. Distilled water also has a
flat taste because it lacks minerals and oxygen. Consequently distilled
water is best utilized in the industrial process rather than in drinking
water.
The process of ion exchange occurs when water seeps through ion-exchange
resins. These ions in the water exchange with ions fixated to the beads.
In this exchange, softening and deionization occurs. The reason for
softening is to reduce the hardness of the water before utilizing the
reverse osmosis (RO) process. Within the softeners are beads that trade
two sodium ions for each calcium or magnesium ion that is taken from the
softened water.
In the process of deionization (DI) beads trade hydrogen ions for
cations, or hydroxyl ions for anion. The cation exchange resins
(composed of styrene and divinylbenzene which contain sulfonic acid
groups) will trade a hydrogen ion for the cations they meet (for example
Na+, Ca++, Al+++). In a similar encounter, the anion exchange resins
(consisting of styrene along with some quaternary ammonium groups) will
trade a hydroxyl ion for any anions (for example Cl-). In this exchange
pure water is formed with the hydrogen ion from the cation exchanger
fusing with the hydroxyl ion of the anion exchanger.
These resins may be bundled in mixed bed exchangers with a mixture of
both types of resins. Or the resins may be packed in individual bed
exchangers with divided units for the cation and exchange beds. In both
cases the resin must be reformed after it has traded all of its hydrogen
and/or hydroxyl ions for charged contaminants existing in the water. In
this way, the
purification process is reversed and the contaminants bound to the DI
resins are replaced with the hydrogen and hydroxyl ions.
The process of deionization is important to the overall water
purification system when it is used with other processes such as RO,
filtration and carbon absorption. Ions are successfully removed through
the DI process, although most organics and microorganisms are not. The
microorganisms affix themselves to the resins causing quick bacterial
growth and ensuing pyrogen generation.
The advantages of deionization are that the process successfully removes
the inorganics that have dissolved; and it is a fairly inexpensive
monetary investment. The disadvantages of this process is that it does
not remove the particles, pryrogens or bacteria effectively; resin
elements and culture bacteria can produce in the DI beds; and there is a
fairly high operating cost involved over the long term.
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