Sewer sytem and its design
What is sewer system?
Sanitary sewer systems are an essential part of modern infrastructure, responsible for transporting sewage from homes and businesses to treatment facilities. These underground pipe networks consist of laterals, submains, and interceptors that convey wastewater by gravity or through pumping stations. Manholes are provided at regular intervals for cleaning, inspection, repair, and connecting sewers to houses.
Design Criteria
- Sewer systems are designed based on the expected sewage flow, which is calculated using the total water consumption and population of the area.
- Minimum velocity (self-cleansing velocity) is important to prevent settlement of solid particles. Typical minimum velocities are 0.6 m/s for sewers flowing full and 0.9 m/s for sewers flowing half full.
- Maximum velocity (limiting velocity) should not exceed 2.4 m/s to avoid abrasion and scouring of the sewer pipe.
Sewer Layout and Sizing
- Sewers should follow the natural slope of the ground as much as possible, with a maximum slope of 1 in 20.
- The recommended minimum sewer size is 20 cm, but it should not be less than 15 cm (10 cm in hilly areas).
- The diameter of the sewer can be determined using the formula.
Materials and Shapes
- Common sewer materials include concrete, steel, plastic, vitrified clay, and brick.
- Sewer shapes can be circular, rectangular, egg-shaped, or other variations depending on the design requirements.
- Connections to existing public sewers can be made through manholes, pre-formed oblique junctions, or core-drilling the barrel of the pipe.
fig: Sewer system