WASTE WATER TREATMENT

All waste water contains large amount of organic molecule e.g from urine or faeces. And contains bacteria.

Waste water must be carefully treated before being released back into the environment.

1) the sewage is screen while passing through a mesh this removes solids and pieces of grit

2) the sewage now settles in large sedimentation tanks, this produces a liquid effluent and sludge which sinks.

3) sludge is taken away and digested by anaerobic bacteria.

In the absence of oxygen this bacteria produces biogas which can be burned for electricity.

At the end the digested sludge can be used as fertilisers for farming.

The liquid effluent contains large amounts of organic molecules and harmful microorganisms. Both of these need to be reduced before the water is returned to the environment.

So air is bubbled through the liquid effluent—> this allows aerobic bacteria to multiply.

In the presence of oxygen, the aerobic bacteria digest the organic molecules and harmful microorganisms. After this liquid effluent can be safely discharged into nearby rivers or the sea.

Sewage treatment

A lot of water is used by industry e.g making paper or chemicals. Fortune water to be treated any harmful chemicals first need to be removed. After the water can enter general sewage treatment. Some parts of the world sewage treatment is used to make potable water.

Might be in exam —→

Easiest way to produce potable water is to use ground water from aquifers. Usually safe to drink once treated with chlorine. Aquifers can sometimes be polluted e.g with fertilisers from farms. So water from aquifers need to be tested carefully.

Where water is scarce—> salt water needs to be desalinated to make potable water , desalination requires a lot of energy and is expensive.