The first compartment of a septic tank must have a liquid volume equal to what fraction of the total liquid volume?

The first compartment of a septic tank is designed to handle the primary treatment of wastewater, allowing for the separation of solids and the initial breakdown of organic matter. A liquid volume equal to one-half to two-thirds of the total liquid volume in the first compartment is optimal for effective sedimentation and proper functioning of the system.

This fraction allows enough space for solids to settle at the bottom, forming a layer of sludge, while also providing sufficient liquid volume for active bacteria to thrive and start the biological treatment process. A volume ratio within this range ensures that the tank can accommodate variations in wastewater flow while promoting an environment that enhances microbial activity necessary for the decomposition of organic materials.

The choice of this fraction reflects industry standards that prioritize effective wastewater treatment while minimizing the risks of system overloading or inadequate treatment, which could lead to system failures or environmental contamination. Keeping the first compartment's liquid volume within this range ultimately supports the longevity and efficiency of the septic system.