left header



The underground conduit for the collection of sewage is called sewer. A network of sewers and appurtenances for the collection and conveyance of sewage generated from each of the properties to sewage pumping station for pumping to sewage treatment and disposal is called Sewage System. There are two types of sewerage system.

1. Separate sewerage system

2. Combined sewerage system.

Separate sewerage system

In separate system of sewerage there are two collection systems or pipe network;

  1. one for collecting domestic sewage as sanitary sewerage system and
  2. another for collecting storm water as storm water drainage system.

The sanitary sewerage systems for domestic sewage are designed for peak sewage flow expected at ultimate stage at the end design period. The storm water drainage systems are designed to carry the maximum storm runoff expected during the critical duration of rainfall.

Separate Sewage Treatment System

Separate Sewage Treatment System

Advantages of separate sewerage system are:

  • The capacity of the water treatment plant will be smaller since only domestic sewage alone is to be treated.
  • Operational problems are less.

Disadvantage of separate sewerage system are:

  • Storm water may always find its way into the domestic sewerage system either through wrong house sewer connections or through manholes and overload the sewage treatment plant.

Combined sewerage system

In Combined system of sewerage both sewage discharge and the storm runoff are collected and conveyed through a common collection system. The ratio of the maximum storm runoff  to sewage flow works out to be 20 to 30.  Hence during non-monsoon period only 1/20th or 1/30th of the design flow, i.e, only the sewage flow is passing through the combined system with very small velocity, resulting in clogging of the systems. Combined sewers are of special types such as egg shaped etc. Combined sewers are , therefore not recommended   for Indian conditions since the rainfall occurs for a period of 3 months or less and there are poor water supplies. In India, only separate sewerage system are adopted.


Combined Sewage System

Advantage of Combined sewerage system are:

  • Only one system is provided and therefore there will not be any confusion in giving connection, and
  • Less expensive to install the system.

Disadvantage of Combined sewerage system are:

  • During non-rainy days the flow will be very meager causing, salivation  requiring frequent cleaning.


  1. Olaoluwa says:

    Pls send to my mail this article.

  2. khalid says:

    thanx for water treatment information

  3. pramod singh says:

    i want to design a sewerage system for 2600 persons over 2.6hectare area.

  4. Abdelmuhdi says:

    Pls email me the article

  5. prashant says:

    pl send me a design calculations of all structures of STP

  6. Didi Rochadi says:

    Pls send me software for calculation sewers system

  7. Iftikhar Leghari says:

    Pl send me the article

  8. onin says:

    want to design a sewerage system for hospital 80 rooms.

  9. Salah ud din says:

    Please send me the desing mannual of an urban water treatment plant?

  10. Jaisi Lal Mandal says:

    plz send me a design calculations of all structures of STP

  11. shreya says:

    can you give me any idea related to drainage system actually i want to make a project for my final year B.E.

  12. amit sharma says:

    i have a project on “design of sewage system” sothat we want more detail on my mail

  13. amit sharma says:

    i take a major project on “design of sewage system” in my college sothat we want more detail on my mail

  14. R.M.Sulemani says:

    Please, please send me some water and wastewater articles

  15. abreha says:

    thank u go on send me other relate this topic

  16. joyce says:

    We are looking for the similar design like the drawing below. The system shall have EQ Tank-Sludge Holding Tank-Aeration Tank-Clarifier Tank. Please propose design drawings and quote

    Consideration for Effluent spec
    1. Ammonium -0.5mg/l
    2. Nitrite – 0.08mg/l
    3. Nitrate – 45mg/l

    1. Tank material – SS316 preferred.
    2. Accessories – TBA by supplier. But the instrumentation best to be Ex-proof type. If not, we can supply ourselve.
    3. How long is the treatment cycle? It shall be taking < 18 hours.
    4. All related drawing of your offering like Material List, Equipment List, GA, Single Line, O&M, Design philosophy etc shall be included.
    5. Spare part. Pls advise us on commission spares, critical spares. We can talk about this later.

    Your response by 13 August 2014 on the above request is appreciated


  17. Seifu says:

    Very good explanation about separate and combined sewarage system. Could you pls send me some more details?.
    Thank you

  18. Haddis says:

    Please send me design calculations for waste water disposal and treatment. Thank you in advance.

  19. Dorina says:

    Am interested in how you explain the difference between the two systems. can you please send me a design which is ecologically sound (using gravity and no energy (electricity needed?

  20. Chhotankumar says:

    Share new an opinion about this subject me on my mail.

Leave a Reply