Biological conversion of biomass (energy crops, agricultural wastes) and various organic wastes is
regarded as a sustainable production of renewable energy in future. Biogas is a versatile renewable energy
source,which can be used for production of vehicle fuel,electric power and heat, chemicals and materials
[1,2,3]. Meanwhile, the production of biogas can drastically reduce greenhouse gases (GHG) emissions
compared to fossil fuels. Another by-product of biogas production named as digestate is an improved
fertilizer in term of its availability to crops which can substitute mineral fertilizer and reduce the nitrogen
leaching from arable land to cycle the nutrient in the ecosystem[3]. It was reported that there are extremely