Explain the function of ‘anaerobic sludge digester’ in a sewage treatment plant

In anaerobic sludge digester, methanogens, i.e. anaerobic bacteria, digest the bacteria and fungi of the floe in the activated sludge.
This produces mixture of methane, hydrogen sulphide and carbon dioxide, i.e. biogas. This gas is used as a source of energy as it is inflammable.