Different Patterns for Wastewater/sewerage Collection

The network of sewers consists of house sewers discharging the sewage to laterals. The lateral discharges the sewage into branch sewers or sub-mains and sub-mains discharge it into main sewer or trunk sewer. The trunk sewer carries sewage to the common point where adequate treatment is given to the sewage and then it is discharged. The patterns of collection system depend upon:

1. The topographical and hydro-logical features of the area.

2. The location and methods of treatment and disposal works.

3. The type of sewerage system employed, and

4. Extent of area to be served.

Following patterns can be adopted for collection systems as per the suitability.

Perpendicular pattern

The shortest possible path is maintained for the rains carrying storm water and sewage.
It is suitable for separate system and partially separate system for storm water drains.
This pattern is not suitable for combined system, because treatment plant is required to be installed at many places; otherwise it will pollute the water body where the sewage is discharged.

Figure: Perpendicular pattern of collection system

Interceptor pattern

Sewers are intercepted with large size sewers.

Interceptor carries sewage to a common point, where it can be disposed off with or without treatment.
Overflows should be provided to handle very large flow.

Figure :Interceptor pattern of collection system

Radial Pattern

It is suitable for land disposal.

In this pattern sewers are laid radialy outwards from the centre, hence this pattern is called as radial pattern.
The drawback in this pattern is more number of disposal works are required.

Figure: Radial pattern of collection system

Fan Pattern

This pattern is suitable for a city situated at one side of the natural water body, such as river.

The entire sewage flows to a common point where one treatment plant is located.

In this number of converging main sewers and sub-mains are used forming a fan shape.

Single treatment plant is required in this pattern.

The drawback in this pattern is that larger diameter sewer is required near to the treatment plant as entire sewage is collected at a common point.
In addition, with new development of the city the load on existing treatment plant increases.