A septic tank is a key component of a septic system, essentially acting as an underground container where wastewater from a home is collected and partially treated. Its main job is to separate solids from liquids before the liquid is dispersed into the drainfield.
The Process Inside the Tank
When wastewater enters the septic tank, it slows down, allowing gravity to do its work. The waste separates into three distinct layers:
- Scum: The lightest materials, such as grease, oils, and fats, float to the top, forming a layer known as scum. The reference specifically mentions this layer and how it's retained.
- Effluent: The liquid layer in the middle is the partially treated wastewater, also called effluent.
- Sludge: Heavier solid particles settle at the bottom of the tank, forming a layer of sludge.
The Role of the Baffle Wall
Many septic tanks are designed with internal structures, such as baffle walls or tees, at the inlet and outlet points. The reference highlights the function of a baffle wall:
- Retention of Solids: The baffle wall helps prevent the solid layers (both scum at the top and sludge at the bottom, referred to collectively as "solids" in the reference) from flowing out of the tank into the drainfield prematurely.
- Direction of Flow: It directs the incoming wastewater downwards and ensures that only the liquid effluent from the middle layer exits the tank.
As the reference states, "because of the baffle wall these solids will be retained within the primary" tank. This retention allows the natural process of anaerobic bacteria within the tank to begin breaking down some of the organic matter in the scum and sludge layers.
What Happens Next?
Once the separation occurs and solids/scum are retained by the baffle wall, the clarified liquid effluent flows out of the tank. This effluent is then typically discharged into a drainfield (also known as a leach field or absorption field), where it is further treated by soil and microorganisms before eventually rejoining the groundwater.
In summary, a septic tank works by receiving wastewater, separating it into layers of scum, liquid, and sludge, and using structures like baffle walls to retain the solids while allowing the partially treated liquid to exit for further processing in the drainfield.
