1.Cow dung cake has low calorific value i.e. 3.1kJ/g than the Methane gas (5.5kJ/g), a biogas constituent.
2.Bio gas is a clean fuel that burns without smoke and leaves no ash, unlike cow dung.
3.The by-product os biogas plants i.e. the spent slurry, being rich in nitrogen and phosphorus is a good manure.