Off Mains Drainage

For the treatment, removal and discharge of wastewater that cannot enter a mains sewage system, there are three commonly-used options. These are the installation of a cesspit, septic tanks or sewage treatment plants.

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Cesspits, also called cesspools, are large tanks buried underground, used to hold all wastewater generated by a property. The wastewater is then collected at regular intervals for disposal at an authorised site.

A septic tank is also a buried tank. It has at least two subdivided chambers. When wastewater enters the first chamber, solid waste sinks to the bottom and scum, which may contain fats and oils, collects on the surface.

The cleaner water in between is allowed to flow into a second chamber where the separation process is repeated. This process can be repeated in a third chamber. If circumstances allow, the water can then be discharged into the ground through a drainage field system.

Sewage treatment plants, also known as package treatment plants, combine the wastewater separation process with bio-treatment.

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First, solids are separated from the water in the same way as with a septic tank. The water is then sent through a mechanical aeration tank, where bacteria is used to further break down harmful waste. The resulting wastewater can then be discharged into a drainage field or watercourse.

Septic tanks can only drain into a drainage field. It must be of a sufficient size, in the right kind of ground, and located far enough away from water courses, such as rivers, streams and drainage ditches.