What does the term "gravity flow" refer to in sewage systems?

The term "gravity flow" in sewage systems refers to the movement of water and waste through pipes and drainage systems purely driven by the force of gravity. This principle is fundamental in designing effective sewage systems, as it allows for the natural drainage of wastewater from homes and buildings to treatment facilities or septic systems without the need for mechanical assistance, such as pumps. By relying on gravity, these systems can operate more efficiently and with lower operational costs, reducing the risk of mechanical failures associated with pumps.

In contrast, flow driven by electric systems is a significantly different approach that involves mechanical energy to move waste. Chemical reactions within sewage pertain to the biological processes that break down organic materials, which is not directly related to how the sewage is transported through the system. Additionally, while water being filtered through soil is a part of the sewage treatment process, particularly in absorption fields, it doesn't define the mechanism of how the wastewater initially moves through the sewage system. Thus, the emphasis on the natural flow due to gravity is what precisely defines "gravity flow."