Combined Sewer System
In this system, only one set of sewer is laid and it carries both sewage and stormwater. The sewage and stormwater are carried to the sewage treatment plant and finally disposed of.
Conditions Favourable for Combined System
The combined system is favoured under the following condition:
1) If the rainfall is small and evenly spread throughout the year.
2) When space available for the laying of sewer is restricted.
3) When pumping is required for sanitary sewage as well as stormwater.
4) When the amount of sewage is less.
Advantages of Combined Sewer System
Following are the advantages of the combined system:
1) The cleaning of sewer is easy as they are large in size.
2) The maintenance cost is less.
3) The stormwater reduces the strength of sewage by dilution.
4) The self-cleaning velocity is easily achieved.
5) This system requires only one set of sewer. Thus it becomes economical.
Disadvantages of a Combined Sewer System
Following are the disadvantages of a combined system:
1) The load on the treatment plant becomes high.
2) The stormwater is unnecessarily polluted.
3) The sewers are large in diameter.
4) This system proves to be uneconomical when pumping is required for the lifting of sewage.
5) During a heavy storm, the combined sewer may be overflown which may create trouble for the people.