(N/A) The agents responsible for decomposing animal dung into biogas are $Anaerobic$ microorganisms (methanogens).
The process involves the following steps:
$1$. Mixing: Animal dung and water are mixed in a $1:1$ ratio to form a slurry in the mixing tank.
$2$. Digestion: The slurry is fed into a digester tank,which is a sealed,oxygen-free chamber. Here,$Anaerobic$ microorganisms break down the organic matter in the dung,producing biogas (primarily methane).
$3$. Collection and Usage: The produced biogas is collected in a gas holder and supplied for use. The remaining slurry,known as spent slurry,is removed and used as a nutrient-rich manure.