Question

why is biogas superior to animal dung cake as a fuel

Answer 1

Burns much cleaner and hotter. As with many other gas fuel

Answer 2

Gas is almost always a better fuel than a solid, for burning. In addition, the liquid and solid fertiliser produced as a by-product of the anaerobic digestion process is a great source on nutrients in any environment where people might be burning animal dung or wood for cooking fuel.