A septic tank works as an underground, watertight container that receives wastewater from a household's toilets, sinks, showers, and other drains. Its primary function is to separate and partially treat the wastewater before it is released into the soil for further natural purification.
How a Septic Tank Works
- Wastewater flows from the house into the septic tank through an inlet pipe. The tank is usually made of concrete, fiberglass, or plastic and is buried underground
- Inside the tank, the wastewater separates into three layers:
- Scum : Lighter materials such as fats, oils, and grease float to the top
* **Sludge** : Heavier solids settle at the bottom and form sludge
* **Effluent** : The middle layer is liquid wastewater that flows out of the tank for further treatment or dispersal
- Anaerobic bacteria (which do not require oxygen) naturally present in the tank break down organic matter in the sludge and scum, reducing their volume and converting some solids into inert matter
- The partially treated liquid (effluent) passes through an outlet pipe, often through an effluent filter that prevents solids from leaving the tank and clogging the drainfield
- The effluent then flows into a drainfield (also called a leach field or soil absorption field), where it is slowly released into the soil through perforated pipes or chambers
- The soil acts as a natural filter, where microorganisms further break down harmful bacteria, viruses, and nutrients, cleaning the water before it reaches groundwater
Summary
A septic tank system treats household wastewater by:
- Settling solids to the bottom (sludge) and floating oils/fats to the top (scum),
- Using bacteria to digest organic waste,
- Allowing clarified liquid effluent to flow to a drainfield,
- Where soil microbes complete the purification process naturally
This process reduces pollution and protects the environment by safely returning treated water to the soil and groundwater.
