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

The primary type of bacteria that digests sewage in a septic tank is anaerobic bacteria. These microorganisms thrive in environments without oxygen and are effective in breaking down organic matter found in sewage. In a septic tank, the lack of oxygen creates ideal conditions for anaerobic digestion, where these bacteria decompose waste and convert it into simpler organic substances and gases.

Anaerobic bacteria play a crucial role in reducing sewage volume and transforming it into effluent that can be discharged more safely into the environment. Their action leads to the production of biogas, which primarily consists of methane and carbon dioxide, a natural byproduct of this digestion process.

While facultative bacteria can also be involved in the process, as they can function in both aerobic and anaerobic conditions, the predominant digestion that occurs in a septic tank is anaerobic. Similarly, aerobic bacteria require oxygen to thrive and are not the primary force in sewage digestion in a septic tank setting. Enzymes, on the other hand, facilitate the biochemical reactions of decomposition but are not a type of bacteria responsible for this process. Overall, the nature of the septic tank environment makes anaerobic bacteria the correct answer for digesting sewage.