Types of Sewers: Navigating Underground Conduits

The term "sewage" describes the liquid waste that people produce on a personal and/or municipal level. It comprises significant quantities of liquid and various components, including both natural and artificial contaminants. Sewage originates from common household activities like bathroom, restroom, or kitchen usage, as well as from industrial, corporate, medical, and manufacturing facilities. Sewage can be classified into two categories: processed wastewater and raw, untreated sewage.

Sewage System

The system responsible for conveying gathered sewage from its origin to a wastewater treatment facility or a designated disposal area is referred to as a sewage system. This sewage system encompasses sewers, manholes, and collection chambers. Sewers, which are subterranean pipes or conduits, serve the purpose of transporting accumulated wastewater (sewage) from its source to its ultimate destination. In this discussion, we will explore sewers and their various categories.

Considerations for Choosing the Right Type of Sewer

When deciding on the kind of sewers for conveyance, the following factors must be taken into account:

Adequate Strength and Durability: The selected sewer system should possess the necessary robustness and resilience to withstand and counteract the forces exerted upon it during transport.

Superior Abrasion Resistance: The selected sewer system should have outstanding resistance to abrasion because sewage contains a variety of impurities that can flow at high velocities and cause surface wear and tear.

Corrosion Resistance: Since sewage contains hazardous gases and highly alkaline water, which can potentially induce corrosion in the sewer system, it is imperative that the sewer material is resistant to such corrosive elements.

Lightweight Design: The sewer system should be designed to be lightweight for ease of handling and installation.

Types of Sewers

Asbestos sewer

An asbestos cement sewer, composed of a blend of asbestos fibres, silica, and cement, serves as a fitting choice for managing household sewage with vertical conveyance requirements, such as from a kitchen sink or bathroom to a collection point. This sewer type offers several advantages, including smooth interiors, ease of cutting, connecting, fitting, and drilling. Additionally, it boasts a lightweight and manageable design. However, it's essential to note that it may not be suitable for high-velocity sewage flow or underground installations. Available in a range of sizes, from 10 to 100 cm in internal diameter and up to 4 metres in length, it should be used cautiously in areas susceptible to sulphate exposure and acid attacks, as these factors can diminish its strength and durability over time.

Brick Sewer: 

As its name suggests, this sewer version is made of a different kind of brick and is mainly used as a stormwater drainage conduit. Noteworthy attributes include its flexibility in construction, allowing adaptation to various shapes and sizes as required. To prevent the intrusion of tree roots, exterior plastering of the joints is applied. These sewers often function as combined systems adept at collecting rainwater, stormwater, and conventional sewage. To ensure a smooth interior surface and enhance corrosion resistance, an internal lining is typically applied.

Cement Sewer: 

The Cement Sewer is crafted from reinforced cement concrete, endowing it with several advantageous properties. Notably, it boasts high resistance to abrasion, ensuring prolonged usage. Its durability and strength are commendable, providing reliability for sewage systems. However, due to its substantial weight, transportation can be challenging. Available in a range of diameters from 150 mm to 900 mm, this sewer type excels at handling high-velocity flows, effectively managing heavy imposed loads with ease.

Cast Iron Sewer: 

Cast iron pipes, fashioned from pig iron, an intermediate industrial material, exhibit a range of desirable qualities. They excel in abrasion resistance, proving their durability over time. However, their costs can be relatively high due to their manufacturing process. These pipes are well-equipped to withstand both high internal and external pressures, making them suitable for applications with substantial flow rates and heavy imposed loads. Their utility extends to inverted syphons, often seen in cross-drainage projects. Cast iron sewers find their niche in areas with dense loads, such as beneath highways and railways, thanks to their robust construction. Their inherent strength and durability stem from their composition. Nevertheless, it's important to note that repairing cast iron sewers can be a challenging endeavour.

Steel Sewer: 

Steel pipes require a galvanised coating for corrosion protection since they lack inherent corrosion resistance. Nevertheless, these pipes exhibit excellent resilience, with the ability to endure high pressure, vibrations, and shocks. However, it's worth noting that they may not be the ideal choice for partial flow sewers, as such applications could potentially expose the conduit to corrosion risks due to their susceptibility to corrosive elements.

Plastic Sewer: 

Plastic sewers have become exceedingly prevalent in contemporary applications. These pipes feature smooth internal surfaces, which enhance their efficiency. Their lightweight construction makes them effortless to handle, and they offer ease in terms of laying, cutting, joining, and fitting. Plastic sewers play a practical role in household drainage projects, catering to such needs effectively. Furthermore, they exhibit impressive durability and resistance to corrosion, adding to their overall reliability.

Shapes of Sewers:

In most cases, sewers adopt a circular shape, which facilitates the smooth transportation of sewage due to their streamlined design. Nevertheless, there are instances where alternative shapes are employed for specific purposes. These alternative shapes may be chosen for economic reasons, to enhance structural strength, or to simplify maintenance procedures.

Conclusion

In conclusion, the world beneath our feet is a labyrinth of sewer systems, each meticulously designed to serve specific purposes and endure varying conditions. From the robustness of cast iron to the cost-effectiveness of stone and ware and the versatility of plastic, we have explored a range of sewer types in this article. These conduits play a critical role in maintaining public health and environmental well-being by efficiently managing wastewater and stormwater. As our cities grow and evolve, the choice of sewer type becomes a crucial decision, balancing durability, cost, and environmental impact. It is through this careful consideration that we continue to build and maintain the vital infrastructure that supports our modern lives.