What are solids that have settled to the bottom of a septic tank called?

The term "sludge" specifically refers to the solids that have settled at the bottom of a septic tank. This accumulation is primarily composed of organic matter, including human waste and other materials that are too heavy to be carried away by the flowing liquid. As the septic tank operates, this sludge forms over time, creating a layer that is crucial for the proper functioning of the tank.

Effluent, in contrast, refers to the liquid waste that exits the septic tank after the solids have settled and some initial treatment has occurred. Infiltrate is associated with the process of liquid or contaminants seeping into the ground or soil, and residuals typically refer to any leftover material after a processing or treatment operation, which doesn’t specifically denote the settled solids in a septic context. Understanding these distinctions is important in recognizing how each term is used within the management of wastewater systems.