What gases are produced in anaerobic sludges digesters ?

Explanation

Sludge is the remainingg part of organic matter after secondary treatment of sewage .
In sludge digesters , other kinds of bacteria , which grow anaerobically , digest the bacteria and the fungi in the sludge .
During this process , bacteria produce a mixture of gases , such as methane , hydrogen sulphide and carbon dioxide which form biogas that can be used as source of energy .