Digester: A digester is where anaerobic (without oxygen) digestion is used to break down sludge and forms biogas. The biogas can be recycled to the digester or used for power generation.

A basic profile of a digester. The layers and size may vary based on its application.

Energy efficiency recommendations at this step would be hard to define unless the facility has a large sludge effluent that could produce biogas for energy production.