Transcript 5.4 - rfisd

The Waterworks
Section 5.4
How does fresh water reach you?

Ancient Romans built aqueducts –
canals to carry water from the mountains
to the city… some are still in use today
At the Waterworks
When reservoirs or rivers are the source,
the water must be treated
 Most water treatment plants occur as
follows:
 INTAKE
 PRIMARY DISINFECTION
 CHEMICAL TREATMENT & MIXING
 FLOCCULATION
 SEDIMENTATION
 FILATRATION
 FINAL CHLORINATION

INTAKE
Intake pipe is in reservoir or river and
covered with a screen to prevent large
objects from entering
 Fish and sticks stay out, but algae and
other small organisms are removed
during treatment

PRIMARY DISINFECTION

Chlorine usually added at first to reduce
the growth of algae and bacteria
CHEMICAL TREATMENT &
MIXING





Several of some or all of the following chemicals
are added to help clean the water
Alum (aluminum potassium sulfate) or iron II
chloride and calcium oxide added to cause small
suspended particles to stick together (called floc)
Sodium hydroxide may be added to raise the pH
and reduce corrosion
Orthophosphate may be added to form a coating
on the pipes, which prevents corrosion and
leaching of lead & copper
Activated carbon is added to reduce chemicals
that cause taste, odor or color
FLOCCULATION
After chemical treatment, water flows
into a large tank with dividers or baffles
 As water moves, more particles stick
together, and the floc grows bigger
 Often, large paddles slowly stir the water

SEDIMENTATION

In a large storage tank, floc settles to the
bottom
FILTRATION
Sometimes, water is pumped to a graded
sand filter with layers of rocks and sand
to remove any remaining particles
 Graded sand filters reduce the frequency
of illness due to Giardia and Cryptosporidia

FINAL CHLORINATION
Chlorine is added in small amounts
before the water leaves the plant
 In some areas, fluoride is also added to
prevent tooth decay
