Problems and profit with waste

Lesson 1

Sewage

Problems with sewage

Apart from no-one wanting to see (or smell) sewage,

It has health risks attached

Typhoid and cholera can be caused by micro-organisms in sewage

Typhoid and cholera

Typhoid bacteria

Cholera bacteria

Cholera Cholera is a water borne disease,

which is typically ingested by drinking contaminated water.

Symptoms include upset gastro-intestinal tract, with diarrhoea and lots of water loss.. Leading to dehydration

There is a high death rate caused by severe deydration.

Typhoid

Causes Typhoid Fever, a high temperature of 39 – 40 degree celsius

The intestines of an affected person can become perforated and they can lose lots of blood, and even die.

How do we avoid these?

We can avoid these and other diseases by having proper sewers to carry sewage away from houses and factories.

However, after earthquakes, sewage pipes can crack and sewage can leak into drinking water.

Sewage treatment In developed countries, sewage is

treated before the water is reused or released into rivers or seas.

A sewage works is where sewage water is treated.

The main process is using micro-organisms to breakdown the sewage by letting them use it as a food source.

Sewage treatment Sewage is filtered to remove solid

debris like rags, paper and grit. The sewage is allowed to settle so the

solid material falls to the bottom of the tank, this is now called sludge.

Sludge can be broken down by micro-organisms in anaerobic conditions to methane and harmless solids used as fertiliser.

Sewage treatment 2 Sewage water (left after sludge is

removed) now passes onto a secondary tank.

Here the sewage is mixed with a big range of micro-organisms all needing oxygen this time.

Compressed air can be pumped through for this.

Sewage treatment 3 This is the activated sludge process

and takes about 6 hours. This can also be achieved by spraying

the sewage over small stones as there are air spaces between the stones

Floating particles are settled out in the final tanks. The water is now clean enough to release into the sea or river.

Quiz – into jotters What dangers to untreated sewage carry? Why do the micro-organisms break down

sewage for us?.. What’s in it for them? Give an example of a useful product

gained from sewage treatment Why do we need a range of micro-

organisms to completely break down sewage?

Which gas is needed in the second stage of sewage treatment?