There they undergo anaerobic digestion, a natural process by which microorganisms digest organic matter and release energy in the form of heat.
(they; undergo; anaerobic digestion; L:There) (microorganisms; digest; organic matter and release energy in the form of heat; L:a natural process)
they microorganisms
undergo digest
anaerobic digestion L:There
organic matter and release energy in the form of heat L:a natural process