Sewage Treatment

Edited by Jamie (ScienceAid Editor)

Sewage Treatment

Sewage is domestic and industrial waste, and water drained from rainfall. Although sewage is mostly harmless (it is 90% water) it contains pathogens that can cause abdominal cramps, diarrhoea, and even paralysis.

Was this helpful? Yes | No | I need help


Activated Sludge

This strangely named method is the most common type of sewage treatment.

diagram of the activated sludge sewage method

First the sewage is screened where larger solid particles, such as stones or bones are removed.

The non-solid remains go to the first settling tank where denser material (the sludge) settles to the bottom and goes to the digester, the fluid will be sent to the oxidation (or aeration) pond.

In the oxidation pond, compressed air is pumped in to vigourously agitate (stir) and aerate (give air) the liquid. Various aerobic bacteria digest and break down organic material, producing nitrates, sulphates, carbon dioxide and water. Any remaining solids are settled out more in the 2nd settling tank. About 10% of this sludge is returned to the oxidation pond.

Was this helpful? Yes | No | I need help

The digester is a large vessel with little air. The sludge is stirred and heated with anaerobic bacteria, these produce methane which is burnt to heat the digester and generate electricity for the sewage works.

Was this helpful? Yes | No | I need help

Treated sludge sludge is dried and used as fertiliser on farms. The treated water will be pumped into rivers or oceans, in some cases it may be reused.


Water treatment is very important because it removes pathogens from water supplies that could cause lethal diseases. In developing countries where there is a poor sewerage infrastructure, millions of children die of diahorrea.

Was this helpful? Yes | No | I need help

Good water treatment is particularly important in areas that do not receive much water. In California for example, sewage is cleaned and then 'recycled' back into the water supply rather than being dumped because of shortages in water supply in such a highly populated yet dry area.

Was this helpful? Yes | No | I need help


ScienceAid welcomes all comments. If you do not want to be anonymous, register or log in. It is free.

Featured Author
166 Articles Started
1,267 Article Edits
42,900 Points
Jamie is a featured author with ScienceAid. Jamie has achieved the level of "Captain" with 42,900 points. Jamie has started 166 articles (including this one) and has also made 1,267 article edits. 8,700 people have read Jamie's article contributions.
Jamie's Message Board
Jamie: Hi, my name is Jamie.
Jamie: Can I help you with your problem about "Sewage Treatment"?

Article Info

Categories : Micro

Share this Article:

Do you have a question not answered in this article?
Click here to ask one of the writers of this article

Thank Our Volunteer Authors.

Would you like to give back to the community by fixing a spelling mistake? Yes | No