Sewage before being disposed of either in river stream or on land, has generally to be treated, so as to make it safe. The degree of treatment required, however, depends upon the characteristics of the source of disposal. Sewage can be treated in different ways. treatment process are often classified as: 1) Preliminary treatment 2) Primary treatment 3) Secondary treatment 4) tertiary treatment 1) PRELIMINARY TREATMENT It consists in solely in separating the floating materials (like dead animals, tree branches, papers, pieces of rags, wood, etc) and also heavy settleable inorganic solids. it also helps in removing the oil and greases etc. from the sewage. Grit chamber or detritus tank for removing grit and sand; and skimming tanks for removing oils and greases. 2) PRIMARY TREATMENT Primary treatment consists in removing large suspended organic solids. this is usually accomplished by sedimentation in settling basins. sometimes, the preliminary as well as primary treatments are classified together under primary treatment the organic solids, which are seperated out in the sedimentation tanks are often stabilised by anaerobic decomposition in a digestion tank or are incenerated. the residue for landfills or soil conditioners 3) SECONDARY TREATMENT Secondary treatment involves further treatment of effluents, coming from the primary sedimentation tank. this is generally accomplished through biological decomposition of organic matter, which can be carried out either under aerobic or anaerobic conditions. in these biological units, bacteria will decompose the fine organic matter to produce a clearer effluent. The treatment reactors, in which the organic matter is decomposed by aerobic bacteria are known as aerobic biological units; and may consists of: (i) Filters : intermittent sand filters as well as trickling filters (ii) Aeration tank: with the feed of recycled activated sludge ( i.e. the sludge which is settled in secondary sedimentation tank, receiving effluents from the aeration tank) (iii) Oxidation ponds and aerated lagoons The treatment reactors, in which the organic matter is destroyed and stabilized by anaerobic bacteria, are known as anaerobic biological units and may consists of anaerobic lagoons, septic tanks, imhoff tanks, etc. out of these units only anaerobic lagoons make use of primary settled sewage and hence, they only can be classified under biological units. septic tanks andimhoff tanks using raw sewage are therefore not classified as secondary units. The organic solids separated out in the primary as well as in secondary settling tanks will be disposed of by stabilizing them under anaerobic process in a sludge digestion tank. 4) FINAL or ADVANCED TREATMENT This treatment is called as tertiary treatment. consists of removing the organic load left after the secondary treatment and particularly to kill the pathogenic bacteria. this treatment, which is normally carried out by chlorination, especially when treated sewage is to be di.

1. Sewage before being disposed of either in river stream or on land, has generally to be treated, so
as to make it safe.
The degree of treatment required, however, depends upon the characteristics of the source of
disposal.
Sewage can be treated in different ways. treatment process are often classified as:
1) Preliminary treatment
2) Primary treatment
3) Secondary treatment
4) tertiary treatment
1) PRELIMINARY TREATMENT
It consists in solely in separating the floating materials (like dead animals, tree branches, papers,
pieces of rags, wood, etc) and also heavy settleable inorganic solids. it also helps in removing the
oil and greases etc. from the sewage.
Grit chamber or detritus tank for removing grit and sand; and skimming tanks for removing oils
and greases.
2) PRIMARY TREATMENT
Primary treatment consists in removing large suspended organic solids. this is usually
accomplished by sedimentation in settling basins.
sometimes, the preliminary as well as primary treatments are classified together under primary
treatment
the organic solids, which are seperated out in the sedimentation tanks are often stabilised by
anaerobic decomposition in a digestion tank or are incenerated. the residue for landfills or soil
conditioners
3) SECONDARY TREATMENT
Secondary treatment involves further treatment of effluents, coming from the primary
sedimentation tank. this is generally accomplished through biological decomposition of organic
matter, which can be carried out either under aerobic or anaerobic conditions. in these biological
units, bacteria will decompose the fine organic matter to produce a clearer effluent.
The treatment reactors, in which the organic matter is decomposed by aerobic bacteria are known
as aerobic biological units; and may consists of:
(i) Filters : intermittent sand filters as well as trickling filters
(ii) Aeration tank: with the feed of recycled activated sludge ( i.e. the sludge which is settled in
secondary sedimentation tank, receiving effluents from the aeration tank)
(iii) Oxidation ponds and aerated lagoons
The treatment reactors, in which the organic matter is destroyed and stabilized by anaerobic

2. bacteria, are known as anaerobic biological units and may consists of anaerobic lagoons, septic
tanks, imhoff tanks, etc. out of these units only anaerobic lagoons make use of primary settled
sewage and hence, they only can be classified under biological units. septic tanks andimhoff
tanks using raw sewage are therefore not classified as secondary units.
The organic solids separated out in the primary as well as in secondary settling tanks will be
disposed of by stabilizing them under anaerobic process in a sludge digestion tank.
4) FINAL or ADVANCED TREATMENT
This treatment is called as tertiary treatment. consists of removing the organic load left after the
secondary treatment and particularly to kill the pathogenic bacteria. this treatment, which is
normally carried out by chlorination, especially when treated sewage is to be disposed off into
river or to be used back for any municipal use.
Solution
Sewage before being disposed of either in river stream or on land, has generally to be treated, so
as to make it safe.
The degree of treatment required, however, depends upon the characteristics of the source of
disposal.
Sewage can be treated in different ways. treatment process are often classified as:
1) Preliminary treatment
2) Primary treatment
3) Secondary treatment
4) tertiary treatment
1) PRELIMINARY TREATMENT
It consists in solely in separating the floating materials (like dead animals, tree branches, papers,
pieces of rags, wood, etc) and also heavy settleable inorganic solids. it also helps in removing the
oil and greases etc. from the sewage.
Grit chamber or detritus tank for removing grit and sand; and skimming tanks for removing oils
and greases.
2) PRIMARY TREATMENT
Primary treatment consists in removing large suspended organic solids. this is usually
accomplished by sedimentation in settling basins.
sometimes, the preliminary as well as primary treatments are classified together under primary
treatment
the organic solids, which are seperated out in the sedimentation tanks are often stabilised by
anaerobic decomposition in a digestion tank or are incenerated. the residue for landfills or soil

3. conditioners
3) SECONDARY TREATMENT
Secondary treatment involves further treatment of effluents, coming from the primary
sedimentation tank. this is generally accomplished through biological decomposition of organic
matter, which can be carried out either under aerobic or anaerobic conditions. in these biological
units, bacteria will decompose the fine organic matter to produce a clearer effluent.
The treatment reactors, in which the organic matter is decomposed by aerobic bacteria are known
as aerobic biological units; and may consists of:
(i) Filters : intermittent sand filters as well as trickling filters
(ii) Aeration tank: with the feed of recycled activated sludge ( i.e. the sludge which is settled in
secondary sedimentation tank, receiving effluents from the aeration tank)
(iii) Oxidation ponds and aerated lagoons
The treatment reactors, in which the organic matter is destroyed and stabilized by anaerobic
bacteria, are known as anaerobic biological units and may consists of anaerobic lagoons, septic
tanks, imhoff tanks, etc. out of these units only anaerobic lagoons make use of primary settled
sewage and hence, they only can be classified under biological units. septic tanks andimhoff
tanks using raw sewage are therefore not classified as secondary units.
The organic solids separated out in the primary as well as in secondary settling tanks will be
disposed of by stabilizing them under anaerobic process in a sludge digestion tank.
4) FINAL or ADVANCED TREATMENT
This treatment is called as tertiary treatment. consists of removing the organic load left after the
secondary treatment and particularly to kill the pathogenic bacteria. this treatment, which is
normally carried out by chlorination, especially when treated sewage is to be disposed off into
river or to be used back for any municipal use.