A Typical Anaerobic Septic System

A conventional septic system  depends on a type of bacterial that can live and digest waste in an environment  that has no oxygen. Such an environment is called Anaerobic. A byproduct is a very corrosive, foul smelling gas that, over years of exposure, can destroy the top and certain parts of your concrete septic tank!

A typical Anaerobic septic system is comprised of three parts:

The conventional anaerobic septic tank that receives the solid and liquid waste (called influent) from the house or business that's connected to it.
The disposal field (leach field) that receives liquid waste (effluent) from the septic tank. The effluent is distributed throughout the disposal field so that it can be absorbed into the surrounding soils.
The soil that purifies the effluent.

The way the three parts operate is actually quite simple. Within the residence or business, solid waste is put into water so gravity can move it away from the building and into the septic tank.

The conventional septic tank is designed to let the majority of these solids settle to the bottom of the tank. This is accomplished by retaining the influent in the tank for several days, allowing the solids to settle to the bottom and the water and floatable solids (scum) to float to the top.

Intestinal bacteria from human bodily wastes survive within the conventional septic tank and there secrete enzymes that assist in breaking down the solid wastes into these two forms.

By this method, 70% to 90% of the solids that were originally put into water are removed and stored within the bottom of septic tank, which eventually need to be pumped out

Over time, these solids build up within the septic tank and have to be removed by pumping and disposed of off site. Typically this means taking the contents or the septic tank (septage) to the local municipal wastewater plant for treatment (digestion) and disposal.

The clarified liquid (effluent) flows out of the septic tank as new influent comes in, and is piped to a disposal field.

The disposal field can be of many designs and constructions. Most typical is the leach line, though all disposal fields have the same function. This function is to expose the liquid effluent to aerobic soils (with oxygen) that can absorb it.

Within the aerobic portions of the soil, there is an abundant community of aerobic microbes, including many species of bacteria that digest the remaining organic matter, purify and recycle the liquid back into the environment.

The part of a conventional septic system that fails is the disposal field.