What is the function of a septic tank in an OSSF?

The function of a septic tank in an On-Site Sewage Facility (OSSF) is to separate solids from liquids and begin the treatment process. The septic tank serves as a critical component of the wastewater management system.

When wastewater enters the tank, it undergoes a process of settling, where heavier solids sink to the bottom and form a sludge layer, while lighter materials like grease and oils float to the top, forming a scum layer. This separation is essential because it allows the clearer liquid effluent in the middle layer to flow into the drain field for further treatment. By beginning the treatment process in this way, the septic tank helps to reduce the volume of solid waste and initiates the breakdown of organic matter through the action of anaerobic bacteria.

This initial treatment is vital in preparing the effluent for subsequent treatment stages, such as soil absorption in the drain field, ultimately ensuring that the effluent is less harmful to the environment and safe for groundwater recharge.