- Septic tank: it is a watertight chamber for the retention,
partial treatment, and discharge for further treatment, of
sewage.
It is a rectangular tank built of masonry below the ground
surface (for detail section of this see figure 11.6) for anaerobic
bacterial action.
The guiding principles in designing a septic tank are:
- To provide sufficient retention time for the sewage
in the tank to allow separation of solids and
stabilization of liquids; - To provide stable quiescent hydraulic conditions
for efficient settlement and flotation of solids; - To ensure that the tank is large enough to store
accumulated sludge and scum; - To ensure that no blockages are likely to occur
and that there is adequate ventilation of gases.