How does a septic tank function?

A septic tank functions primarily by separating solids from liquids within the wastewater that it receives from a household. As wastewater enters the tank, it undergoes a process of stratification where heavier solids settle at the bottom to form sludge, while lighter materials, such as grease and oils, float to the top to create a scum layer. The liquid effluent, which is the treated wastewater, remains in the middle layer and is able to flow out of the tank into the drain field for further treatment and distribution into the soil.

This separation process is crucial for effective treatment because it allows the liquid effluent to be filtered through the soil in the drain field, where it is naturally purified before re-entering the groundwater system. This mechanism is essential for maintaining hygiene and environmental safety, as it helps prevent the contamination of local water sources.

The other choices describe processes that are not part of the functioning of a septic tank. For instance, while a septic tank does store some wastewater, it is not a permanent storage solution nor is it designed for chemical treatment of wastewater, which are functions associated with different types of sewage treatment systems. Similarly, filtering out impurities from drinking water is not within the purview of a septic tank. These distinctions clarify why the chosen answer accurately