Sewage Treatment

Question 1

Screening & Grit Removal

Answer 1

The first stage of treatment removes large materials such as plastic bags and twigs and grit by screening

Question 2

Sedimentation

Answer 2

Sedimentation comes next which occurs in a settlement tank. The water is allowed to stand still in the tank while heavier solids sink to the bottom creating sewage sludge, whilst lighter matter which is also known as effluent, floats to the top

Question 3

Aerobic Digestion

Answer 3

The effluent is removed and treated by biological aerobic digestion
This involves pumping air into the water to encourage the breakdown of organic matter and other microbes by aerobic bacteria

Question 4

anaerobic

Answer 4

Anaerobic digestion is then used to break down the sewage sludge from the bottom of the settlement tank. It is firstly removed and placed in large tanks where bacteria break it down
Anaerobic digestion releases methane gas as a by product from the organic matter in the sludge. Methane gas is used as a source of energy and the leftover, digested waste as a fertiliser

Question 5

When there are toxic substances within waste water, it is important to use additional phases of treatment

Answer 5

This can include using membranes, adding additional chemicals e.g. to precipitate metals out of solution, and also U.V. radiation