A traditional system uses a specific process to purify household wastewater. Specifically, this system uses an initial tank to pre-treat the effluent. This tank, known as a septic tank or all water tank, collects all the wastewater from the dwelling.
After this stage, the pre-treated water is infiltrated into the soil already in place for the spreading trenches. This second treatment stage can also be carried out in reconstituted soil in the case of sand filters or mounds.
Purification is therefore twofold: physical purification by filtration, and bacterial purification by the bacteria present in the soil.