C14.3 Treating waste water

Question 1

What happens when the sewage first arrives at the pumping station?

Answer 1

➢ It goes to be screened at the sewage treatment plant

Question 2

What happens during screening?

Answer 2

➢ The sewage arrives and the first step is to remove large grit and solid objects - passes through a metal grid

Question 3

What happens after screening?

Answer 3

➢ It goes into Primary treatment

Question 4

What happens during primary treatment?

Answer 4

➢ In the 1st circular tank, the solid sediments are settled from the mixture
➢Large paddles rotate pushing the solids called sludge towards the centre of the tank
➢ Then the sludge is piped to a storage tank
➢ The effluent(watery liquid) above sludge contains harmful microorganisms and is stored in the second tank

Question 5

What happens during the secondary treatment?

Answer 5

➢ In the second tank, useful bacteria feed on the effluent of any remaining organic matter and harmful microorganisms still present, breaking them down aerobically
➢ The tank is aerated by bubbling air through the wastewater

Question 6

What happens during the Final treatment?

Answer 6

➢ The useful bacteria are allowed to settle out to the bottom of the tank as a sediment
➢ Sediment is either recycled back into the secondary treatment tank or passed into the tank where the sludge is treated
➢ Wastewater is safe enough to be discharged back into rivers

Question 7

How is sewage sludge treated?

Answer 7

➢ Most can be dried and used as a fertiliser on farmland to improve the soil or used as a source of renewable energy

Question 8

How can biological treatment be carried out on the sludge?

Answer 8

➢ Can be carried out at about 55 degrees which can take up to 30 days to complete
➢ Breakdown of products include biogas
➢ Biogas can be burned and used to power the sewage treatment plant or provide electricity
➢ Or the sludge can be dried into a crusty solid that can be burnt to generate electricity