Septic Tank: Introduction
A septic tank is used as a pretreatment.
The septic tank receives the wastewater and removes solids from liquid.  As the wastewater enters the tank, the
flow rate is reduced and heavy solids settle, forming sludge. Grease and other light solids rise to the surface,
forming a scum layer.
The septic tank provides (partial) anaerobic biological treatment. Scum and sludge are stored and are digested
over time.
Important is to ensure the anaerobic conditions and to provide sufficient effective volume and therefore sufficient
retention time.
Constructed Wetlands