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Screening
Large objects removed from the sewage using a metal grid
Primary treatment
Solid sediments allowed to settle and the sludge is pumped to a storage tank. The effluent moves to the next tank
Secondary treatment
Useful bacteria added to break down harmful microorganisms aerobically
Final treatment
Useful bacteria allowed to settle and can be reused or put with sludge
It can be put through a bed of sand and sterilised with UV light or chlorine
Uses of sludge
Can be dried and used for:
burn to generate electricity
fertiliser
Note 
Flashcard (32)