Separate system of sewage:

• The Separate system of sewage provides two separate systems of sewers, the one intended for the conveyance of foul sewage only and the other one is for the rain water, including the surface washing from certain street, overflow from public bath & foundation etc.
• The sewage from the first system of sewers can be led to the treatment works, while the flow from the second system of sewers can be directly discharge into the natural streams without any treatment.

Advantages :

• The cost of installation is low. • The loads on the treatment unit are less because only foul sewage is carried out by separate sewer need to treat. • The sewage in the separate system will be more uniform character and so will lend its self more easily to purification.

Disadvantages :

• Since the sewers are of small size, it’s difficult to clean, and they likely to get chocked. • Two sets of sewers may ultimately prove to costly. • Strom water sewers or drains may come in use only during rainy season. During other part of the year, these may severs as dumping place of garbage & may get chocked.

Combined system of sewerage:

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

Advantages :

• This system requires only one set of sewers, hence the maintenance cost are reduced. • The sewers are of large size, and therefore their chance of choking are rare also, it’s easy to clean. • The strength of sewage is reduced by dilution.

Disadvantages :

• Cost of construction is very high because of large dimensions. • Due to the inclusion of storm water, the load on the treatment unit is increased. • The system is uneconomical in the circumstances when pumping is required for lifting of sewage. • Storm water is unnecessarily polluted.