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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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MECHANICAL FILTRATION OF DRINKING WATER
Mechanical
filtration will remove almost all forms of turbidity. Of course, the smaller
the turbid particles, the finer must be the filter openings in order to
strain them out. Under some circumstances the openings have to be so small
that they cause an excessive pressure drop as the water percolates through
the filter, and the unit may be impractical. In many cases filters containing
specially graded and sized gravel and sand are effective in screening
out turbid particles. With such units a periodic backwashing to remove
the filtered material is all the maintenance necessary.
Some filter manufacturers
also provide a "filter-aid" which is added onto the top of the
filter bed immediately after backwashing. The filter-aid traps fine dirt
particles, producing a more sparkling clear water and keeps dirt from
penetrating the filter bed, insuring better bed cleansing during backwashing.
In some cases cartridge filters are effective. These will filter water
used for cooking and drinking. Generally these cartridge filters are just
installed on the drinking water lines.
There are several reasons
for this: (1) they produce a significant pressure drop. This would be
a handicap if these filters were installed on the main water line. (2)
Their replacement cost may be too high to justify their use in filtering
all the water.
Municipal and industrial
systems frequently make use of the coagulation process to aid in the removal
of turbidity. In this economical process a coagulating agent, such as
aluminum sulfate, is fed into the water. After rapid mixing, the coagulating
agent forms a "floc" generally in the form of a gelatinous precipitate.
This floc gives the appearance of a soft, gentle snowfall.
A settling period is
then needed to allow the floc to fall gently through the water. As the
floc forms and settles, it tends to collect or entrap the turbid particles
and form them into larger particles which sink to the bottom. On large
installations settling basins provide the necessary time and space for
the process. After the settling period, the water flows through a filter
to remove the last traces of the coagulant and any remaining turbid particles.
Small coagulation-filtration
systems are sometimes utilized for household purposes when turbidity is
particularly offensive. The difficulties with the use of this process
for home purposes are in determining what type of coagulant will give
best results, and what equipment is required.
Experience in this
area is essential because the chemical properties of the water must be
considered in relation to the coagulant or combination of coagulants
employed. Further, adequate mixing and coagulation times are essential.
Coagulation-filtration also requires considerably more attention to maintenance
than do the simple filtration processes mentioned earlier.
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