Sewage treatment includes following steps: (i) Primary Treatment
It is a physical process of removal of small and large particles through filtration and sedimentation.
The first step is to remove the floating objects (like polythene bags) by letting the sewage to pass through wire mesh screens of sequential smaller pore sizes.
Sewage is then passed into the grit chamber, where grit is sedimented.
Sewage is then allowed to pass into the settling tank, where the suspended materials settle down to form primary sludge.
Effluent is then taken for the secondary treatment.
(ii)Secondary Treatment
It is a biological process in which bacteria naturally occurring in sewage are used.
Effluent obtained from the primary treatment is passed into large aeration tank. Here, it is constantly agitated and air is pumped into it.
Due to this, rapid growth of aerobic bacteria occur into floes. These consume the organic matter of the sewage and reduce the BOD.
Effluent is passed into settling tank, where the floes are allowed to settle forming the activated sludge.
A small amount of activated sludge is pumped back into aeration tank as inoculum.
The remaining major part of the activated sludge is pumped into anaerobic sludge digesters, where the anaerobic bacteria digest the organic matter and produce methane, hydrogen sulphide and carbon dioxide.
Effluent is then allowed to pass into the water body.
Explain the different steps involved in sewage treatment before it can be released into natural water bodies.
Answers
Praveen
Sewage treatment includes following steps:
(i) Primary Treatment
(ii)Secondary Treatment