Waste water treatment

Question 1

Different sources waste water comes from

Answer 1

use at homes like going to the toilet, when you flush -> water down the drain -> goes into sewers and towards sewage treatment plants

2) Agriculture systems produce a lot of waste water including nutrient run-off from fields and slurry from animal farms

Question 2

Different sources waste water comes from and the treatment of them

Answer 2

Sewage from domestic or agriculture sources has to be treated to remove any organic matter and harmful microbes before its put back into fresh water sources like rivers or lakes. Otherwise it would make them very polluted and would pose health risks

Industrial processes also produce a lot of waste water that has to be collected and treated
As well as organic matter, industrial waste water also contain harmful chemicals - so it has to undergo additional stages of treatment before it is safe to be released into the environment

Question 3

Some of the processes involved in treating waste water at sewage treatment plants include : 1-3

Answer 3

1) before treated, the sewage is screened - removes large bits of material as well as any grit

2) then its allowed to stand in a settlement tank and undergoes sedimentation - heavier suspended solids sink to bottom to produce sludge while lighter effluent floats to top

3) Effluent in the settlement is removed and treated by biological aerobic digestion ( air is pumped through water to encourage aerobic bacteria to break down any organic matter - including other microbes

Question 4

Some of the processes involved in treating waste water at sewage treatment plants include : 4 - 6

Answer 4

4) Sludge from bottom of settlement tank is removed and transferred to a larger tank. Here its broken down by bacteria using anaerobic digestion

5) Anaerobic digestion breaks down the organic matter in the sludge releasing methane gas in process. Methane is then used as an energy source and remaining digested waste used as fertiliser

6) For waste water containing toxic substances, additional stages of treatment may involve adding chemicals, UV radiation or using membranes

Question 5

Advantages and disadvantages of sewage treatment

Answer 5

Advantage : uses less energy than the desalination of salt water so could be used as alterative in areas where fresh water is lacked.

disadvantages : requires more processes than treating water