Which of the following devices is considered a primary treatment device for sewage?

A septic tank is a primary treatment device for sewage because it provides the initial treatment of wastewater by allowing solids to settle out and providing a biological environment for anaerobic bacteria to break down organic matter. In a septic tank, the wastewater enters and the heavier solids settle to the bottom, forming a sludge layer, while lighter materials such as oils and grease float to the top, forming a scum layer. This separation allows for the partial decomposition of organic matter, reducing the pollutant load before the effluent is released for further treatment.

The other devices, while important in the wastewater treatment process, serve different roles. The stabilization pond is often used for secondary treatment, utilizing sunlight, algae, and bacteria to treat wastewater. An intermittent sand filter also functions as a secondary treatment option, filtering effluent through sand to remove additional impurities after primary treatment. The aeration tank promotes aerobic biological treatment, which is a more advanced stage of treatment focusing on breaking down pollutants in a controlled environment using airflow to support microbial activity.