Transcript Water Supply and Sewage - Mr Andrews` Science Space!

Water Supply and
Sewage
Year 7
Unit 4.4
Water debate
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Is it ok to drink recycled sewage?
With Australia in the grips of a drought our
government are looking at the possibility of
recycling our waste water for drinking
You decide if it ok…
Pure water
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Does it come from the sky?
Is tap water pure water?
What other chemicals are we drinking with our
water?
Do they do us harm? Or are they good for us?
Rainwater
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Is a mixture – it comes into contact
with a number of substances which
can dissolve into it
What substances could rain come
into contact with?
Treatment
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For us to drink water from the dams the water
must go through a number of treatments to
make sure it is safe. POTABLE WATER
Flocculation
Filtration
Sterilization (Chlorine)
Balancing pH
Fluoridation
Flocculation
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Chemicals called FLOCCULANTS are added to
make tiny particles clump together
The clumps (FLOC) either float and are
skimmed off the top, or sink to the bottom and
form sediment
Filtration
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The water is pumped through filters to remove
any particles
Chlorine
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Is added to kill germs and bacteria that can
cause diseases
Also called STERILISATION
Chlorine can be added as a liquid or a gas
Lime and Soda ash
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The presence of chlorine, fluorine and other
chemicals causes the pH balance of water to be
changed.
Adding Lime and Soda ash to the water balances
the pH so it is neutral (not acidic or basic)
Fluorine
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Is added to our water to help prevent tooth
decay
Water flow
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Water is moved from the dams or weirs into
treatment tanks, before it is stored in reservoirs.
Large pipes then move the water into populated
areas for use.
Where do we get our water from? Hint it is not
a dam or weir!!
Unusual sight
This is the
Mundaring Weir,
east of Perth.
The last time it
overflowed was in
1994.
Were you born
then??!
Sewage vs Sewerage
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Sewage
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Sewerage
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Waste and water mixture
that we put into our
drains, down sinks, into
toilets etc.
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The network of pipes
and tanks that collect
and move sewage
away from homes and
built up areas
Septic tanks?
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Does anyone have a septic tank in their house?
Only a few years ago were some areas of Mullaloo
connected to the sewerage system
Septic tanks rely on bacteria to break down sewage
and release it back into the soil.
Certain chemicals should not be used in septic
tanks as they will kill the ‘good’ bacteria
Taken a swim lately?
It all ends up in the ocean
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Sewage treatment plants involves the activated sludge
process.
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Screening– sewage is sieved to remove large objects
Aeration– sewage moves to an aeration tank where air
is pumped in to help the bacteria continue feeding on
the sewage. The gas produced by the bacteria may be
collected to power the turbines for the aerators
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It all ends up in the ocean con.
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Settling– Chemical are added in the aeration
tank to convert any dissolved wastes into solids.
The sewage is moved into a settling tank where
the solid particles sink into a thick sludge
Filtration– the sewage is moved into a pebble
bed filter tank which separates out the
suspended solids
We are almost there…
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Sterilisation– UV light or chlorination is used
to disinfect the sewage
Output– the sludge is dried out and stored. It
can be then sold as fertiliser. The ‘treated’
sewage is then released into the ocean
How much water do you use?
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It is estimated each Australian uses 57L of water
a day
But according to our water usage meters we use
much more than that.
24,000 gigalitres a year, with 70% used on
irrigation!
We may need to look at recycling water to help
our climate along.