What type of bacteria primarily digests sewage in a septic tank?

In a septic tank, the primary function of bacteria is to break down organic matter found in sewage. Anaerobic bacteria are the main microorganisms involved in this process because they thrive in environments lacking oxygen, which is characteristic of septic tanks. These bacteria ferment and decompose organic material, releasing gases and creating a byproduct that is less harmful than the original waste.

Anaerobic bacteria are capable of breaking down complex organic substances without the need for oxygen, making them well-suited for the anaerobic conditions present within a septic tank. This process is crucial to the functioning of a septic system as it reduces the volume of waste and helps in the treatment of pollutants before the effluent is discharged into the leach field.

In contrast, while facultative bacteria can operate in both aerobic and anaerobic conditions and contribute to waste processing, they do not dominate the digestion process in a septic tank as anaerobic bacteria do. Aerobic bacteria require the presence of oxygen and, therefore, are more effective in treatment systems designed for aeration rather than in a septic tank's anaerobic environment. Enzymes, while they assist in the breakdown of substances, are not types of bacteria and do not perform the digestion process independently within the septic tank.