Waste water treatment C14.3

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What is waste water?
(name four things that it has been used for)
Water that has been used for:
- flushing
- personal hygiene (eg showers)
- washing clothing
- agriculture
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What does waste water contain?
- organic molecules
- harmful microorganisms
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What must happen before waste water it is released back into the environment?
It must be treated before it's released back into the environment
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Why must waste water be treated before disposal into rivers?
There may be harmful bacteria in waste water
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What are the four stages of treating waste water?
1) screening
2) sedimentation
3) breaking down solids
4) breaking down liquids
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What are the semi-solids called?
Sludge
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What is the liquid called?
Effluent
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What is screening?
It is stage one - the large solids and grit are removed
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What is sedimentation?
It is stage three - the sediments settle in the tank. The sludge and effluent are separated as the sludge sinks to the bottom of the tank
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How is the sludge broken down?
The sludge is digested by anaerobic bacteria (without oxygen)
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What gas does digesting the sludge produce?
Methane
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What is the methane gas used for?
It is used for generating electricity
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What is the sludge used for in agriculture?
The sludge is used as fertiliser, to improve the soil
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Fill in the gaps:
The effluent contains lots of _______ ________ and _______ ____________ which need to be removed
The effluent contains lots of ORGANIC MOLECULES and HARMFUL MICROORGANISMS which need to be removed
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How is the effluent broken down?
Aerobic bacteria digests the organic molecules and harmful microorganisms (with oxygen)
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What can happen after the waste water treatment is complete?
The water can be put back into lakes and rivers.
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How do you turn fresh water eg from rain into drinking water?
1. Choose an appropriate source of fresh water
2. Pass the water through filter beds to remove any solids
3. Sterilise to kill microbes with chlorine, ozone or ultra-violet light
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What issues are there with the sterilising agents?
(chlorine, ozone, UV)
Chlorine is a toxic gas so the amount added
to water has to be carefully monitored.
Using ultraviolet light to kill microbes avoids
adding chemicals to the water but is more expensive.
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Why is it more difficult to produce drinking water from waste water than from water in lakes (fresh water)?
Drinking water must be clean.
Waste water must undergo treatment and this requires high amounts of energy (it must be heated) and it takes lots of time (you must wait 30 days)
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What is potable water?
Water that is safe to drink (not pure water as it still contains dissolved solid substances)

It has sufficiently low levels of dissolved salts and microbes.
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How can sea water be turned into drinking water?

What issue is there with these processes?
Desalination, via distillation or reverse osmosis

They require large amounts of energy
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What happens during reverse osmosis?
Sea water is passed through a membrane that only allows through the water molecules. It needs high pressure to push the water through the membrane. The high pressure requires a lot of energy to produce.
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Other cards in this set

Card 2

Front

What does waste water contain?

Back

- organic molecules
- harmful microorganisms

Card 3

Front

What must happen before waste water it is released back into the environment?

Back

Preview of the front of card 3

Card 4

Front

Why must waste water be treated before disposal into rivers?

Back

Preview of the front of card 4

Card 5

Front

What are the four stages of treating waste water?

Back

Preview of the front of card 5
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