Transcript Water Treatment

Water Treatment
To know how water is made potable
To know the stages of freshwater
treatment in order
Preliminary Treatment
• Any physical, chemical or mechanical
process used on water before main
treatment.
• Screening is used to remove rocks, sticks
and other debris.
• Chemicals may be added to control algae
growth
• Presedimentation settles
out sand, grit and gravel.
Coagulation
• Removes small particles made up of microbes,
silt and other suspended material.
• Treatment chemicals (e.g. alum) are added to
the water and mixed rapidly.
• The chemicals cause small particles to clump
together (coagulate).
• Gentle mixing brings smaller clumps together
into larger groups called “floc”
Flocculation
• The heavy, dense floc settles to the
bottom of the water in large tanks.
• This can be a slow process.
• Once the floc settles, the water is
ready for the next stage.
Clarification / Sedimentation
• This occurs in a large basin, water flows
very slowly.
• Sludge (solids and water) accumulates
at the bottom of the basin.
• The sludge is pumped or scraped out for
disposal.
• Clarification is also known
as sedimentation.
Softening and Stabilization
• Water that contains many minerals is called
“hard water”.
• This forms limescale and causes many problems
in pipes.
• If too many minerals are removed, the water is
too “soft” and causes pipe corrosion!
• Drinking water plants keep the balance between
hard water and soft water.
• Minerals are added to soft
• water, or removed from hard
• water.
Filtration
• Water is turbid when it contains suspended
matter.
• Filtration removes this suspended matter.
• The suspended matter can consist of
microorganisms, floc, algae, silt and metal
precipitates.
• Suspended materials are filtered
out as water passes through beds
of granular material.
• The beds are made with layers
of sand and gravel.
Fluoridation and Disinfection
• Fluoride is added to water to reduce tooth decay!
• It is an economical process endorsed by public health
groups.
• Fluoride is placed into the water system either as a
solution or a powder.
• Disinfection destroys disease causing organisms,
chlorine is most commonly used for this.
•It is important to add just the
right amount of chlorine as it
dissipates quickly so disinfection
has to be ensured before the
water leaves the plant.
Holding Tanks
• Finished water is stored in
holding tanks.
• These provide a reserve of
water to meet the changing
water demands of the
communities they serve.