Definition: A septic tank is a tank typically underground, in which sewage is collected and allowed to decompose through bacterial activity before draining by means of a soakaway.
A septic tank is made of concrete, fiberglass, PVC or plastic, to collect domestic wastewater (sewage).

The term "septic" refers to the anaerobic bacterial environment that develops in the tank which decomposes or mineralizes the waste discharged into the tank.

The rate of accumulation of sludge—also called septage or fecal sludge—is faster than the rate of decomposition. Therefore, the accumulated fecal sludge must be periodically removed which is commonly done with a vacuum truck.

Today, the design of the tank usually incorporates two chambers, each equipped with a manhole cover, and separated by a dividing wall with openings located about midway between the floor and roof of the tank.

Wastewater enters the first chamber of the tank, allowing solids to settle and scum to float. The settled solids are anaerobically digested, reducing the volume of solids. The liquid component flows through the dividing wall into the second chamber (called soakaway) where further settlement takes place. The excess liquid, now in a relatively clear condition, then drains from the outlet into the septic drain field/ underground.

For the water to percolate into the soil, the floor of the soakaway is unsealed.
However, in water logged areas, i.e placed with high water level, the floor of the soakaway is completely sealed to avoid underground water from coming in. The waste water in this chamber is thus vacuum out or the chamber is provided with pumps/ siphons to regularly drain the water.



We continue tomorrow