8.11 Sewage Treatment

Describe best practices in sewage treatment.

• Primary treatment of sewage is the physical removal of large objects, often through the use of screens and grates, followed by the settling of solid waste in the bottom of a tank.
• Secondary treatment is a biological process in which bacteria break down organic matter into carbon dioxide and inorganic sludge, which settles in the bottom of a tank. The tank is aerated to increase the rate at which the bacteria break down the organic matter.
• Tertiary treatment is the use of ecological or chemical processes to remove any pollutants left in the water after primary and secondary treatment.
• Prior to discharge, the treated water is exposed to one or more disinfectants (usually, chlorine, ozone, or UV light) to kill bacteria.
• Enduring understanding STB-3: Human activities, including the use of resources, have physical, chemical, and biological consequences for ecosystems.