The document discusses three common sewerage systems: 1. Combined system - Carries both sewage and stormwater in a single sewer, reducing costs but increasing treatment loads. 2. Separate system - Uses two separate sewer systems for sewage and stormwater, reducing treatment loads but increasing costs. 3. Partially separate system - Admits early stormwater runoff but diverts excess, combining advantages of combined and separate systems while requiring stormwater overflows. The document provides details on the advantages and disadvantages of each system.

1. GOVERNMENT ENGINEERING
COLLAGE BHAVNAGAR
(CIVIL ENGINEERING DEPARTMENT)
TOPIC: SEWERAGE SYSTEMS
PREPARE BY……..Mayank Oza

2. SEWERAGE SYSTEMS
There are three systems of sewerage adopted
in practice:
1…..combined system
2…..Separate system
3…..Partially separate system

3. 1. Combined system
When both sanitary sewage and storm water
are carried in a single sewer, it is called a
combined sewer system.
When the flow in a combined sewer consist of
only domestic sewage and industrial waste
without storm water, flow is called ‘DRY
WEATHER FLOW’

4. Advantages
Both domestic sewage and storm water are
carried in a single sewer, so construction cost is
less.
The strength of domestic sewage is reduced
because of dilution of storm water.
The sewers are of large size, and therefore the
chances of their chocking are rare. It is easy to
clean them.
In town with narrow street, this systems is
preferred.

5. Disadvantages
Initial cost is high because of large dimensions
of sewers.
Because of large size of sewer, their handling
and transportation is difficult.
Due to the inclusion of storm water, the load
on the treatment plant increase.
During heavy rain the sewer may be overflow
and may thus create unhygienic conditions.
If the whole sewage is to be disposed off by
pumping it is uneconomical.

7. 2.Separate system
In this system two separate sets of sewer are
installed, one for collection and conveyance of
sanitary sewage and other for storm water.
As storm water is carried separately, it is not
foul in nature and normally disposed off to
natural water coarse without any treatment.
Where as the sanitary sewage is taken to
treatment plant separately and after requires
treatment it is disposed off.

8. Advantages
Size of sewer requires less.
Since the sanitary sewage and storm water floes
in a separate pipes, the quantity of sewage to be
treated is less.
As the sewer are smaller in section, they can be
easily ventilated.
During disposal if the sewage is to be pumped,
the separate system is cheaper,
Rain water can be discharge in to steams without
any treatment.

9. Disadvantages
Since the sewer are smaller size, it is difficult
to clean them.
They are likely to get chocked.
Initial cost is high, when two separate set are
used.
Maintenance cost of sewer is also high.
Generally self cleaning velocity is not available
due to small quantity of sewage therefore,
flushing is required at various point.

10. Separate system

11. 3. Partially separate system
In this system, only one set of underground
sewer is laid.
These sewer admit the sanitary sewage as well
as the early washings from the drainage area
due to rains.
When the storm water exceed its specified
limit, the excess is diverted in to natural water
courses.

12. Advantages
 The sewer are of reasonable size. Their
cleaning is therefore not difficult.
 It combines the advantages of both the
separate as well as the combined systems.
 The work of house plumbing is reduced,
because the rain water from roof, sullage
from baths and kitchen, etc. can be taken in
the pipe carrying the discharge from the
water closest.

13. Disadvantages
During dry weather floe deposition take place
in sewer.
As initial storm water is included the cost of
pumping and size of disposal units increase.
The storm water increase the load on
treatment units.
There are possibilities of over flow, requiring
the construction of storm water overflow.