Sewage Treatment
Primary Treatment (Physical Treatment)
Filtration
Floating debris (sequential filtration)
Sedimentation
Grit (soil and small pebbles)
Secondary Treatment (Biological Treatment)
Agitated in aeration tanks (air is pumped mechanically)
Flocs grow
Consume major part of the organic matter in effulent
Reduces biochemical oxygen demand
Passed into settling tanks
Gives activated sludge
Anaerobic sludge digester
Anaerobic bacteria digests bacteria and fungi
Produces biogas (Inflammable)
Effluent is released in water bodies
Methane (CH4)
Carbon dioxide (CO2)
Hydrogen Sulphide (H2S)
masses of bacteria associated with fungal filament to form mesh like structures
amount of oxygen that would be consumed if all the organic matter in 1 L of water was oxidised by bacteria, BOD ∝ Polluting potential
Primary Sludge (sediments)
Effluent (Supernatant)
Taken for the next stage
small amount is added to aeration tank as inoculum