How a Septic System Works
A septic system has two main components:
The septic tank and the soil absorption system (SAS).
The Septic Tank
A septic tank is the first and primary treatment component in a septic system. When water flushes down the drain, it connects to the main sewer pipe leading from your house to your septic tank. When the water enters the tank it becomes wastewater. This wastewater settles and the solids separate from the liquids and form layers in the tank.
There are three layers in the septic tank.
The bottom layer is called the sludge layer. This is where solids in the tank settle and are decomposed by naturally occurring (anaerobic) bacteria.
The top layer is called the scum layer. This is where grease and other floatable materials gather at the top of the septic tank until pumped out. This is the layer you see when you look down a septic cleanout. It is a GOOD SIGN to see this layer. This means your tank is working properly and the baffles are trapping solids, preventing them from clogging up your soil absorption system.
The middle layer is called effluent. It is the mostly solid free layer that flows out of the tank through the baffle and outlet pipe and enters the distribution box.
The distribution box is a small but crucial component to a septic system. When the effluent leaves the tank, it flows into the distribution box and settles for a quick moment before flowing out through one or more drain pipes that lead to the absorption field.
The Soil Absorption System (SAS)
The most complex component of a septic system is the soil absorption system. This is commonly referred to as a drainfield. This is the area where secondary treatment occurs and effluent absorbs into the surrounding soils.
Drainfield trenches and the soils surrounding them are very efficient at treating dirty septic water. They filter out the bad components, leaving behind a cleaner and clearer water. This water will eventually end up in ground waters or surface waters, which is why it is so crucial that sewage is treated before reaching these water sources.
For more information read our blog post on how septic systems work.