This municipal waste water is called sewage.
Major component of waste water is human excreta.
For a sewage less polluting to make sewage treatment plants (STPs).
This treatment carried out in two stages :
1. Primary treatment
2. Secondary treatment
1. Primary treatment
First process in primary treatment called filteration.
Second process in primary treatment called Sedimentation.
Fresh floating water removed by sequential filteration (effluent) .
And some particles are settled down called primary sludge. This process called Sedimentation.
2. Secondary treatment or biological treatment
Involvment of living microbes.
Flocs - association of bacteria and fungus filament.
The primary effluent is passed into large aeration tank.
In aeration tank is presence of air/O2.
Due to the availability of air or oxygen microbes(Flocs) growth easily.
Oxygen increase - flocs increase
Function of flocs : Oxidise the organic matter present in the sewage.
Flocs need and demand of oxygen.
BOD : Biochemical oxygen demand.
BOD - the amount of oxygen consumed by the microbes (flocs) to Oxidise
1 litre of organic matter.
Secondary treatment continously untill BOD is reduced.
Flocs again passed on aeration tank from the settling tank and they act as inoculum. This flocs called activated sludge.
The effluent passes through a large tank called anaerobic sludge digester.
Growth of bacteria in absence of oxygen in anaerobic sludge.
Remaining flocs will be dead.
Example of anaerobic bacteria : methanogens
Methanogens purify and clean the water.
And produced some gases such as methane, CO2, hydrogen sulphide.
Some steps started from the government
1. GAP - Ganga action plan.
2. YAP - Yammuna action plan.
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