Waste water treatment

Question 1

What are the main sources of waste water?

Answer 1

• Domestic: houshold waste from showers, toilets and sinks
• Agricultrual: waste from farm animals and nutrient run off
• Industrial: waste from factories that make and use chemicals

Question 2

Why does industrial waste water require extra steps to treat?

Answer 2

• Often contains harmful chemicals which aren’t present in domestic and agricultural waste

Question 3

What are the steps of sewage treatment?

Answer 3

• Screening: water is passed through a mesh to filter out any large things
• Sedimentation: sewage is left to sit in a settlement tank. This leads to the heavier, solid bits of the mixture sink to the bottom to form sludge and the lighter particles at the top to form effluent
• Break down organic matter

Question 4

How is organic matter broken down in sewage treatment in the two different tanks and what is done with the broken down waste?

Answer 4

• Sludge and effluent are transferred to two different tanks
• Sludge is in anaerobic conditions and effluent is in aerobic conditions
• Sludge is broken down by anaerobic digestion and effluent is broken down by aerobic digestion
• Effluent: water is now safe and can be released into the environment
• Sludge: anaerobic digestion produces methan which is captured and burned as an energy source. Digested waste is used as a fertiliser

Question 5

Sewage treatment vs desalination

Answer 5

• Sewage water treatment is easier than desalination therefore, countries with little fresh water tend to rely on sewage water treatment

Question 6

What extra steps are required for industrial waste treatment?

Answer 6

• Contains toxic substances so requires extra steps
• Toxic substances removed by adding chemicals or exposure to UV light