Operator terms · Wastewater
What is a digester in wastewater treatment?
A digester is a tank where microorganisms break down wastewater sludge, reducing its volume and stabilizing it so it is safer to handle and dispose of. Digestion can be anaerobic, without oxygen, or aerobic, with air. It is a core step in the solids side of a plant.
Last reviewed 2026-08-03
What it does
Microorganisms consume the organic matter in sludge, which cuts the volume, reduces odor and pathogens, and leaves a more stable material.
Aerobic and anaerobic
Aerobic digestion adds air for the microbes; anaerobic digestion works without oxygen and can produce methane gas. Both stabilize the sludge.
Common questions
- Why digest sludge?
- To reduce its volume and stabilize it before disposal.
- What is the difference between aerobic and anaerobic?
- Aerobic uses air; anaerobic works without oxygen and can make methane.
- What comes out of a digester?
- Stabilized sludge that is handled as biosolids.