resources - waste water treatment

Question 1

what is water used for?

Answer 1

• drinking (small amount)
• personal hygiene eg baths + showers (large amounts)
• flushing toilets + washing clothes
• agriculture

Question 2

what does waste water contain?

Answer 2

large amount of organic molecules eg from urine and faeces. contains harmful microorganisms like bacteria. so waste water must be carefully treated before being released back into the environment

Question 3

how is waste water treated?

Answer 3

• first, sewage is screened by passing throng a mess to remove solids and grit
• now sewage settles in large sediment tanks. this produces liquid effluent and a semi-solid sludge which sinks

Question 4

what happens to sludge produced in sediment tanks from waste water?

Answer 4

sludge taken away and digested by anaerobic bacteria. in absence of oxygen, these bacteria produce biogas which can be burned for electricity. at the end, digested sludge can be used for fertilisers for farming

Question 5

what has to happen to the liquid effluent from sediment tanks?

Answer 5

liquid effluent has organic molecules and harmful microorganisms which both need to be reduced before returning to environment. they bubble air through the liquid to allow aerobic bacteria to multiply. in presence of oxygen, aerobic bacteria digest the organic molecules and harmful microorganisms. after, liquid effluent can be safely discharged into local water

Question 6

what is a lot of water used by? how is this waste treated?

Answer 6

industry eg in making paper and chemicals
any harmful chemicals first need to be removed. water then enters general sewage treatment. in some countries this technique is used to produce potable water (not in Uk)

Question 7

compare 3 ways to produce potable water (aquifer, salt water and sewage water)

Answer 7

• easiest way. use ground water and aquifers. usually safe to drink once treated with chlorine. aquifers can sometimes be polluted with eg fertilisers from farms so water needs treating carefully
• sewage water it takes many purification steps so only done in places where water is scarce

-salt water needs desalinated to produce potable water which requires lot of energy + expensive