Sewer Network

Published: | Updated: August 20, 2020;

Definition - What does Sewer Network mean?

A sewer network, which forms the main component of a sewerage system, is defined as a conglomeration of pipes and sewers that work together to collect and drain wastewater from the population or industrial centers to off-site treatment facilities. At the treatment facility, the waste is treated to prevent any disease spread before being returned to the environment.

In built up environments, the sewer network consists of a serious of pipe networks that drain buildings and city blocks. Special drainage outlets connect the lines of the sewer network running within individual facilities to the group network. Typically, small pipes leave our homes and other buildings and join trunk sewers that are much larger in diameter. A primary element of the sewer network is the manhole, which is vital for routine inspection and repairs.

Several factors influence the design of a sewage network, including ground conditions, topography, effluent composition, and construction sequencing. These factors determine whether networks are transverse, perpendicular, parallel, zonal, or radial. Wastewater that flows through the sewer system can be transported either through gravity flow or implementing the use of pumping stations in situations where gravity flow is not possible.

Trenchlesspedia explains Sewer Network

A sewer network can be a combined system where sanitary wastewater and stormwater are carried in the same pipeline. It can also be a single system that operates separately to the stormwater pipeline.

Combined Sewer Networks

Pipelines that make up combined sewer networks are sized to accommodate large rainfall events and significant amounts of stormwater and equipped with relief points to prevent flooding.

When there are large amounts of rainwater in the sewer system, the water tends to be discharged directly into the sea or river without treatment, thereby possibly negatively affecting the environment through pollution.

The combined sewer network can be designed with temporary storage areas to treat the stormwater before it is discharged into a large body of water. Another method of curbing the problem is the use of swirl concentrators, which create a vortex that concentrates impurities in a smaller volume of water, allowing for treatment. Due to the environmental concerns related to combined sewer networks, separate sewer networks are increasingly more common.

Figure 1: Combined Sewer System (source)

Separate Sewer Networks

Separate networks carry either stormwater or domestic sewage. In the case of stormwater sewage networks, stormwater is brought to its discharge point or stored in detention basins. Storm sewer networks consist of reinforced concrete or corrugated metal pipes that allow gravity flow to the discharge area. Pumping stations are avoided as much as possible since large pump capacities would be required.

The wastewater sewer network is usually divided into smaller units consisting of the lateral, collector, trunk, and intercepting sewer.

  • Lateral Sewer – These are the smallest in the network and receives sewage from the community then discharges into the collector sewer.

  • Collector Sewer – The collector sewer receives sewage from two or more lateral sewers and ties into the main interceptor.

  • Trunk Sewer – The trunk sewer is the main sewer that receives flow from two or more collectors.

  • Intercepting Sewer – These are usually constructed from precast reinforced concrete pipes. Intercepting sewers receive wastewater from both the collector and trunk sewers and transport the wastewater to the treatment plant.

Where population density is low or site conditions are not conducive for a traditional sewer network, other systems are implemented, including pressure sewers, vacuum sewers, and small diameter gravity sewers with septic tanks.

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