Is Hydrogen gas present in biogas? As it is highly inflammable, may it ignite the other gases like methane?
The constitution of the biogas depends greatly on its source and the fermenting microbe. But in general, it does contain hydrogen about 0-1%. Even if it did contain large amounts, the mixture would be inflammable, but it would not burst into flames without any external igniter, which could be any small fluctuation of heat if the mixture is too unstable. But in general, an inflammable gas doesn't start burning on its own.
The auto ignition temperature of a combustible mixture of hydrogen in air is 500 degrees C source - Wikipedia. It will not spontaneously ignite, some part of it must first reach that temperature through a spark, flame, or other heat source. Once it ignites, the methane of course will burn too.