Which gases are produced when anaerobic bacteria grow in a medium containing cellulose?

In $STPs$,in which tank is biogas produced during the process?

What is the group of bacteria responsible for the production of biogas called?

Select the correct option for $Methanogens$.

Which bacteria are used in a biogas plant?

Consider the following statements about methanogenic bacteria:
$I.$ Methanogenic bacteria are commonly found in the anaerobic sludge formed during sewage treatment.
$II.$ These bacteria also occur in the rumen of cattle,where they act upon cellulosic material to break down cellulose.
$III.$ They play a very important role in the nutrition of cattle by digesting cellulosic material.
Which of the statements given above are correct?