Waste water treatment

Question 1

What happens in the first stage of waste water treatment?

Answer 1

The sewage is screened-this involves removing any large bits of material as well as any grit

Question 2

What happens in the second stage of waste water treatment?

Answer 2

• The water is allowed to go in a sedimentation tank where it undergoes sedimentation
• The heavier solids sink to the bottom to produce sludge
• The lighter effluent floats on the top

Question 3

What happens to the sludge?

This is still the second stage

Answer 3

The sludge gets taken away and is digested by anareobic bacteria and at the end the sludge can be used as fertilisers

Question 4

In the absence of oxygen what does the anaerobic bacteria do

Answer 4

The anaerobic bacteria produces biogas which can be burned for electricity

Question 5

In the presence of oxygen what does the anaerobic bacteria do?

This is part of stage 3 of waste water treatment

Answer 5

It digests the organic molecules and harmful microoragnisms

Question 6

What happens in stage 3 of the sewage water treatment?

effluent at the top

Answer 6

The effluent in the settlement tank is removed and treated by biological aerobic digestion.This is when air is pumped through the water to encourage aerobic bacteria to break down organic matter

Question 7

What is stage 4 in sewage water treatment?

Bottom of the tank

Answer 7

The sludge from the bottom of the settlement tank is also removed and transferred into large tanks where it gets broken down by bacteria in a process called anaerobic digestion

Question 8

What is stage 5 in sewage water treatment?

Answer 8

Anaerobic digestion breaks down the organic matter in the sludge releasing methane gas in the process

Question 9

What is stage 6 in sewage water treatment?

Answer 9

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