What is the purpose of a septic tank in the sewage treatment process?

The purpose of a septic tank in the sewage treatment process is primarily to trap solids for settlement. When wastewater enters the septic tank, it undergoes a separation process where heavier solids settle to the bottom of the tank, forming a sludge layer, while lighter materials, such as grease and oils, float to the top, creating a scum layer. This separation is crucial as it allows the bacterial action within the tank to begin the breakdown of organic materials, promoting preliminary treatment of the sewage.

By facilitating the settling of solids, the septic tank plays a pivotal role in preventing solids from entering the leach field or drain field, which can lead to clogging and system failure. This function is essential in maintaining the efficiency and longevity of the entire septic system, making it an integral part of on-site sewage treatment in areas without centralized sewer systems. Thus, the correct answer effectively highlights this fundamental aspect of septic tank operation.