Question

Answer please please

Answer 1

Becoz while burning it directly it here is cow dung releases a lot of smoke which pollutes the environment. Also it has very low calorific value. So it is not a good fuel.
Whereas biogas which is decomposed cow dung and waste does not release smoke and has high calorific value. That is why we use biogas instead of heating it directly.
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Answer 2

when biomass is burnt directly it realeases a lots of smoke alongwith some toxic gases which are very hazardous for life as well as environment. Moreover,when biogas is burnt it doesn't provide a lots of heat enegy. But when biomass is converted into biogas, biogas appears to be smokeless and emits a large amount heat. So biogas is financially good and environmentally very beneficial.
hope it helps....