Septic tanks are devices for treating and filtering feces. The principle is that solid matter decomposes at the bottom of the tank, while the water-soluble matter rises to the top and flows out through pipes, preventing blockages. This allows sufficient time for the solid matter (faeces and other waste) to hydrolyze. A septic tank refers to a small treatment structure that separates and sedimentates domestic wastewater and undergoes anaerobic digestion of sludge.

A septic tank is a fundamental facility for sludge treatment and also serves as a pre-treatment facility for domestic wastewater, its function being:

1. Ensure the cleanliness of residential community environments, preventing the spread of domestic wastewater and pollutants.

2. Eliminate mosquito, fly, and worm eggs in the anaerobic digestion environment of septic tanks.

3. Temporary storage of sludge, anaerobic digestion for organic sludge, matured organic sludge can be used as agricultural fertilizer.

4. Pretreatment of domestic wastewater, sedimentation of impurities, and hydrolysis of large molecular organic matter into smaller molecules like acids and alcohols, improving the subsequent wastewater treatment.