Humans and the environment

04.30.2020
09:10:36

Biology / grade 10- Today’s topic- Sewage treatment- course book - pages 309 and 310.

Main points-
Sewage Treatment
As human population grows, the need for fresh water increases.
A significant amount of water we consume is used to flush away human waste (sewage) into pipes .

The pipes carry the sewage and water to treatment plants where the organic waste is removed and the water cleaned so it can be returned to natural water sources without causing eutrophication.

Crude sewage flows through a screen in which large materials like paper and sticks are trapped so they can be removed and burned.

The sewage is passed slowly through channels where grit and other heavy particles picked up along the way settle to the bottom – the grit is later washed and returned to the land.

The channels lead into sedimentation tanks where the solid material settles on the bottom as sludge and the liquid part, called effluent, remains on top.

The sludge is removed by pumping it into tanks where anaerobic bacteria decompose it – often the bacteria produce methane which can be collected and used as an energy source for the plant.

The effluent (liquid) is treated with aerobic bacteria to remove any organic waste in it, before being treated with chlorine to kill the bacteria.

At this point it is clean enough to return to natural water systems or be passed on to a second treatment plant where it is processed further to make it pure enough to reuse as drinking water.

Water containing sewage goes through several stages of treatment before being returned to natural water systems.














Homework is given- workbook-Eutrophication-page 140 and 141.