SEWERAGE SYSTEMS :-

 

            SEWERAGE SYSTEMS :-

             The sewerage system is divided into three types –

1.                           3. Separate system :

The separate system provides two separate system of sewers the one intended for the conveyance of foul sewage only, such as fecal matter, domestic waste matter etc. and the second for the rain water , including the surface washing from certain streets, overflow from public baths etc.

Advantages :

1.    The cost of installation is low.

2.    The storm water can be disposed off through the open channels along the road sides.

3.    The load on the treatment units will be lowered , since only the foul sewage carried by the separate sewers need the treated .

4.    There is no necessity of providing automatic flushing tanks, for used in dry weather, because the flow in a sewer of smaller section is much more efficient.

            Disadvantages :

1.    Since the sewer is small size, it is difficult to clean them .

2.    They are likely to get chocked.

3.    Two sets of sewer may ultimately prove to be costly.

2.                      2.   Combined System :

            The combined system provides only one sewer to carry both the foul sewage as well as the rain                     water. The sewage and rain water are carried to this sewage treatment plant , before its                                  final disposal.

Advantages :

1.    The system requires only one set of sewers . hence the maintenance costs are reduced.

2.    The sewers are of larger size , and therefore the chances of their choking are rare.

3.    The strength of the sewage is reduced by dilution. 

            Disadvantages :

1.    The cost of construction is very high because of large dimension of the sewers.

2.    Because of large size of the sewers, their handling and transportation is difficult.

3.    The system is uneconomical in the circumstances when pumping is required for lifting of sewage.

 3.  Partially combined system :In this system, only one set of underground sewer is laid. These sewers admit the foul sewage as well as the early washings by rains. As soon as the quantity of storm water exceeds a certain limit, the storm water overflow, and is thus collected and conveyed in open drains to the natural streams .

 

 Advantages :

1.    The  sewers are of reasonable size. Their cleaning is therefore not very difficult.

2.    It combines the advantage of both the separate as well as the combined systems .

3.    The problem of disposing off storm water from homes is simplified.

             Disadvantages :

1.    The storm water increase the load on the treatment units.

2.    The storm water also increase the cost of pumping.

3.    During the dry weather , when there is no rain water, the velocity of flow will be low. Thus self cleaning velocity of sewer may not be achieved.