A septic tank is a device for treating feces and filtering out sediment. Its principle is that solid matter decomposes at the bottom of the tank, while the liquid matter above flows into the pipes and away, 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 anaerobically digests sludge.

Septic tanks are fundamental facilities for sludge treatment and also serve as pre-treatment for domestic wastewater, playing a role in:

1. Ensure environmental hygiene in residential communities, 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 of organic sludge, matured organic sludge can be used as agricultural fertilizer.

4. Pretreat domestic wastewater to sediment impurities and hydrolyze large molecular organic matter into smaller molecules like acids and alcohols, improving subsequent wastewater treatment.