What is the spent slurry (leftover sludge) in biogas production used for?

Which gas is known as gobar gas?

Biogas produced by anaerobic fermentation of biomass waste contains ......

The diagram below represents a typical biogas plant. Select the correct option for what $A$,$B$,and $C$ refer to.

Which of the following provides both energy and fertilizer?

Methanogens,particularly $Methanobacterium$,grow anaerobically on cellulosic material and produce:
$I.$ Methane
$II.$ Carbon dioxide
$III.$ Oxygen
$IV.$ Ethane
Choose the correct option.