GOVERNMENT ENGINEERING COLLAGE BHAVNAGAR

(CIVIL ENGINEERING DEPARTMENT)

TOPIC: SEWERAGE SYSTEMS

PREPARE BY……..Mayank Oza

SEWERAGE SYSTEMS

There are three systems of sewerage adopted in practice:

1…..combined system 2…..Separate system 3…..Partially separate system

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’

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.

DisadvantagesInitial 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.

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.

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.

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.

Separate system

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.

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.

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.

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