Sewerage systems

SEWERAGE SYSTEMS

The term, "sewerage systems" refers to a network for the collection of wastewater and convey it via pipes from its point of origin to the point of discharge into the environment.

1. If the drainage is carried alongwith the sewage, it is called a combined system
2. If the drainage and sewage are taken inndependently of each other through two different sets of conduits, the sewerage system is called a separate system
3. If the domestic sewage is admitted into pipes meant for storm water discharge and vice versa depending on the requirement, the sewerage system is called partially separate system.
4. Although it is advantageous and economical to construct a 'separate system', in big cities and towns it is not possible to attain a truly separate system as some rain water may always find its way into municipal sewer system
5. A separate system requires laying of two different conduits making it more expensive
6. Separate conduits cannot be laid in congested streets and localities as it is physically unfeasible
7. Sewer pipes in combined system are liable to frequent silting in non-monsoon season or they will have top be laid at steep slopes requiring more excavation and pumping thereby making them more expensive
8. In a combined system, less foul storm water get mixed with highly foul sewage water requiring treatment with entire flow. Thus treatment plant needs to have a higher capacity making it costlier
9. In case of combined system, flooding and backing up of sewers may occur due to excessive rains
10. Sewer lines are laid at steeper slopes compared to storm water drains resulting in pumping of only sewage and no pumping of storm water resulting in lower pumping cost for separate system

The economy of both  systems should be worked out for each individual project along with physical feasibility befor deciding on the type of sewerage system to be adopted.