Water filtration
Introduction
There are many uses of water in industry and, in most cases, the used water also needs treatment
to render it fit for re-use or disposal. Raw water entering an industrial plant often needs treatment
to meet tight quality specifications to be of use in specific industrial processes.
Water treatment
is any process that improves the quality of water to make it more acceptable for a specific end-
use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance,
water recreation or many other uses, including being safely returned to the environment. Water
treatment removes contaminants and undesirable components, or reduces their concentration so
that the water becomes fit for its desired end-use.
Steps of water treatment
Screening
Water from lakes, rivers or the ground passes through a screen as it enters the water treatment
plant. When the water source is a lake or river, the screen serves an important function, keeping
out large natural contaminants such as plants and wood, or fish. If ground water is used,
screening may not be necessary since the water has passed through layers of the earth in what is
essentially a natural screening function
Coarse screens remove large solids and typically have openings of 6 mm (0.25 in) or
larger
Fine Screens are typically used to remove material that may create operation and
maintenance problems in downstream processes, particularly in systems that lack primary
treatment. Typical opening sizes for fine screens are 1.5 to 6 mm (0.06 to 0.25 in). Very
fine screens with openings of 0.2 to 1.5 mm (0.01 to 0.06 in) placed after coarse
Coagulation
Treatment plant workers add alum and other chemicals to the water, which cause tiny sticky
particles, or floc, to form. These floc attract dirt particles, making them eventually heavy enough
to sink to the bottom of the water storage tank.
Coagulation is a chemical process that involves neutralization of charge whereas flocculation is a
physical process and does not involve neutralization of charge. The coagulation-flocculation
process can be used as a preliminary or intermediary step between other water or wastewater
treatment processes like filtration and sedimentation. Iron and aluminium salts are the most
widely used coagulants but salts of other metals such as titanium and zirconium have been found
to be highly effective as well.
Sedimentation
is the tendency for particles in suspension to settle out of the fluid in which they are entrained
and come to rest against a barrier. This is due to their motion through the fluid in response to the
forces acting on them: these forces can be due to gravity, The water and floc flow into a
sedimentation basin. As the water sits there, the heavy floc settle to the bottom, where they
remain until removal.
Filtration
Water flows through a filter designed to remove particles in the water. The filters are made of
layers of sand and gravel, and in some cases, crushed anthracite. Filtration collects the suspended
impurities in water and enhances the effectiveness of disinfection
Disinfection
Water goes into a closed tank or reservoir. Chlorine or other disinfecting chemicals kill any
remaining microorganisms or bacteria in the water and help keep the water clean until
distribution. If a water treatment facility uses ground water as its only water source, disinfection
may be the only step required to sufficiently treat the water. After it is disinfected, the purified
water sits in the closed tank or reservoir until it flows through pipes to homes and businesses.
Physical methods
◦ Heating to boiling – heating the water until it reaches its boiling point.
◦ Irradiation with uv rays – is a disinfection method that uses short-
wavelength ultraviolet (UV-C) light to kill or inactivate microorganisms by
destroying nucleic acids and disrupting their DNA, leaving them unable to
perform vital cellular functions. The dosage, a product of UV light intensity and
exposure time, is usually measured in microjoules per square centimeter, or
equivalently as microwatt seconds per square centimeter (µW·s/cm2).
Chemical methods
◦ Chlorination - Chlorine inactivates a microorganism by damaging its cell
membrane. Once the cell membrane is weakened, the chlorine can enter the cell
and disrupt cell respiration and DNA activity (two processes that are necessary for
cell survival).
