Sanitary sewer

Sewage treatment is less effective when sanitary waste is diluted with stormwater, and combined sewer overflows occur when runoff from heavy rainfall or snowmelt exceeds the hydraulic capacity of sewage treatment plants.

Vertical pipes, usually made of precast concrete, called manholes, connect the mains to the surface.

[4] Pipes conveying sewage from an individual building to a common gravity sewer line are called laterals.

Minimum sewer diameters are often specified to prevent blockage by solid materials flushed down toilets; gradients may be selected to maintain flow velocities generating sufficient turbulence to minimize solids deposition within the sewer.

[6] Force mains are typically constructed of welded steel or HDPE jointed to resist pressures within the pipe.

[9] Simplified sanitary sewers consist of small-diameter pipes, typically around 100 millimetres (4 in), often laid at fairly flat gradients (1 in 200).

Holding infiltration to acceptable levels requires a higher standard of maintenance than necessary for structural integrity considerations of combined sewers.

[11] A comprehensive construction inspection program is required to prevent inappropriate connection of cellar, yard, and roof drains to sanitary sewers.

In the mid-1950s a unit was invented where two units at each end with a special cement mixture in between was pulled from one manhole cover to the next, coating the pipe with the cement under high pressure, which then cured rapidly, sealing all cracks and breaks in the pipe.

These methods may be unsuitable for locations where the full diameter of the original pipe is required to carry expected flows, and may be an unwise investment if greater wastewater flows may be anticipated from population growth, increased water use, or new service connections within the expected service life of the repair.

Animal feces accumulated on city streets while animal-powered transport moved people and goods.

Accumulations of animal feces encouraged dumping chamber pots into streets where night soil collection was impractical.

[15] Combined sewers were built to use surface runoff to flush waste off streets and move it underground to places distant from populated areas.

Sanitary sewer installation with PVC pipe. Sanitary sewers are sized to carry the amount of sewage generated by the collection area. These sewers are much smaller than combined sewers , which are designed to also carry surface runoff .
Manhole access to sewer
Schematic of a conventional sanitary sewer to convey blackwater and greywater from households to a centralized sewage treatment facility. [ 3 ]
A manhole cover for a sanitary sewer access point.
View looking down into an open manhole showing two converging sanitary sewer lines. The larger line enters from the right and changes direction within the manhole to exit from the top of the photo. A smaller line enters from the bottom of the photo under the access steps. The concrete floor of the manhole has channels to minimize accumulation of solids.
Interior of a large sanitary sewer viewed from an access manhole chamber.
Stoneware sanitary sewer (bottom) submerged in trash and fecalia
Old brick sanitary sewer from second half of the 19th century. Prague , New Town