SEPARATE AND PARTIALLY SYSTEM OF SEWAGE
1) SEPARATE SYSTEM OF SEWAGE
2) COMBINED SYSTEM OF SEWAGE
3) PARTIALLY COMINED OR PARTIALLY SEPARATE SYSTEM
1 SEPARATE SYSTEM OF SEWERAGE
In this system two sets of sewers are laid .The sanitary sewage is carried through sanitary sewers while the storm sewage is carried through storm sewers. The sewage is carried to the treatment plant and storm water is disposed of to the river.
1) Size of the sewers are small
2) Sewage load on treatment unit is less
3) Rivers are not polluted
4) Storm water can be discharged to rivers without treatment.
1) Sewerage being small, difficulty in cleaning them
2) Frequent choking problem will be their
3) System proves costly as it involves two sets of sewers
4) The use of storm sewer is only partial because in dry season the will be converted in to dumping places and may get clogged.
2 COMBINED SYSTEM OF SEWAGE
When only one set of sewers are used to carry both sanitary sewage and surface water. This system is called combined system.
Sewage and storm water both are carried to the treatment plant through combined sewers
1) Size of the sewers being large, chocking problems are less and easy to clean.
2) It proves economical as 1 set of sewers are laid.
3) Because of dilution of sanitary sewage with storm water nuisance potential is reduced
1) Size of the sewers being large, difficulty in handling and transportation.
2) Load on treatment plant is unnecessarily increased
3) It is uneconomical if pumping is needed because of large amount of combined flow.
4) Unnecessarily storm water is polluted
3 PARTIALLY COMINED OR PARTIALLY SEPARATE SYSTEM
A portion of storm water during rain is allowed to enter sanitary sewer to treatment plants while the remaining storm water is carried through open drains to the point of disposal.
The sizes of sewers are not very large as some portion of storm water is carried through open drains.
Combines the advantages of both the previous systems. Silting problem is completely eliminated.
1. During dry weather, the velocity of flow may be low.
2. The storm water is unnecessary put load on to the treatment plants to extend.
3. Pumping of storm water in unnecessary over-load on the
.1Suitable conditions for separate sewerage systems:-
A separate system would be suitable for use under the following situations: Where rainfall is uneven.
Where sanitary sewage is to be pumped.
The drainage area is steep, allowing to runoff quickly.
Sewers are to be constructed in rocky strata. The large combined sewers would be more expensive.
2 Suitable conditions for combined system:-
Rainfall in even throughout the year.
Both the sanitary sewage and the storm water have to be pumped.
The area to be sewered is heavily built up and space for laying two sets of pipes is not enough.
Effective or quicker flows have to be provided.
After studying the advantages and disadvantages of both the systems, present day construction of sewers is largely confined to the separate systems except in those cities where combined system is already existing. In places where rainfall is confined to one season of the year, like India and even in temperate regions, separate system are most suitable.
The quantity of sewage to be treated is less, because no treatment of storm water is done.
In the cities of more rainfall this system is more suitable.
As two sets of sewer lines are to laid, this
system is cheaper because sewage is carried in underground sewers and storm
In narrow streets, it is difficult to use this system.
Less degree of sanitation is achieved in this system, as storm water is disposed without any treatment.
As the treatments of both are done, the treatment is costly.
In the cities of less rainfall this system is suitable.
Overall construction cost is higher than separate system.
It is more suitable in narrow streets.
High degree of sanitation is achieved in this system.