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Method for sewage treatment
Water is passed through a mesh to remove large substances and grit
Water is allowed to settle in large sedimentation tanks, causing it to form liquid effluent and semi-solid sludge
The sludge sinks and is taken away to be digested by anaerobic bacteria
In the absence of oxygen, anaerobic bacteria digest sludge into biogas used for energy
At the end, digested sludge can be used for fertilisers
Air is bubbled through the liquid effluent to allow aerobic bacteria to multiply
In the presence of oxygen, bacteria digest organic molecules and harmful microorganisms
Liquid effluent is then discharged into rivers
What needs to happen to water from industry before sewage treatment
treated for harmful chemicals
Aquifers
safe when treated with chlorine
may be polluted by fertilisers so needs to be tested
Sewage
lots of purification steps=$$$
so only in countries where water is scarce
Desalination
lots of energy=$$$