What is the primary function of a septic tank in treating household wastewater?

The primary function of a septic tank in treating household wastewater is to separate settled and floatable suspended solids from the liquid. This process is fundamental in managing sewage because the septic tank provides a controlled environment where solids can settle at the bottom, forming sludge, while lighter materials such as oils and greases float to the top, forming scum.

This separation is vital for the treatment process as it allows the clearer liquid effluent to flow out of the tank into the drain field (or leach field), where further treatment occurs as the effluent percolates through the soil. The tank essentially acts as a settling chamber, facilitating the initial breakdown and treatment of wastewater before it is further treated in the soil, making it an essential component of a septic system.

Decomposing organic material is a part of the process, but it is a secondary role that occurs over time within the tank rather than the primary function of action. Filtering wastewater through fins and producing methane gas are not primary functions of the septic tank; rather, those aspects relate more to the workings of other systems or biological processes occurring as a result of the treatment within the tank.