Transcript Problems and profit with waste

Problems and profit with waste
Lesson 1
Sewage
Problems with sewage
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Apart from no-one wanting to see (or
smell) sewage,
It has health risks attached
Typhoid and cholera can be caused by
micro-organisms in sewage
Typhoid and cholera
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Typhoid bacteria
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Cholera bacteria
Cholera
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Cholera is a water borne disease,
which is typically ingested by drinking
contaminated water.
Symptoms include upset gastrointestinal tract, with diarrhoea and lots
of water loss.. Leading to dehydration
There is a high death rate caused by
severe deydration.
Typhoid
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Causes Typhoid Fever, a high
temperature of 39 – 40 degree celsius
The intestines of an affected person can
become perforated and they can lose
lots of blood, and even die.
How do we avoid these?
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We can avoid these and other diseases
by having proper sewers to carry
sewage away from houses and
factories.
However, after earthquakes, sewage
pipes can crack and sewage can leak
into drinking water.
Sewage treatment
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In developed countries, sewage is
treated before the water is reused or
released into rivers or seas.
A sewage works is where sewage water
is treated.
The main process is using microorganisms to breakdown the sewage by
letting them use it as a food source.
Sewage treatment
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Sewage is filtered to remove solid debris like
rags, paper and grit.
The sewage is allowed to settle so the solid
material falls to the bottom of the tank, this is
now called sludge.
Sludge can be broken down by microorganisms in anaerobic conditions to methane
and harmless solids used as fertiliser.
Sewage treatment 2
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Sewage water (left after sludge is
removed) now passes onto a secondary
tank.
Here the sewage is mixed with a big
range of micro-organisms all needing
oxygen this time.
Compressed air can be pumped through
for this.
Sewage treatment 3
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This is the activated sludge process and
takes about 6 hours.
This can also be achieved by spraying
the sewage over small stones as there
are air spaces between the stones
Floating particles are settled out in the
final tanks. The water is now clean
enough to release into the sea or river.
Quiz – into jotters
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What dangers to untreated sewage carry?
Why do the micro-organisms break down
sewage for us?.. What’s in it for them?
Give an example of a useful product gained
from sewage treatment
Why do we need a range of micro-organisms
to completely break down sewage?
Which gas is needed in the second stage of
sewage treatment?