Global warming, energy security, and the rising costs of oil have added a greater driving force to the
development of feasible alternatives to petroleum-based transportation fuels. In parallel, wastes and
wastewater generated from various industries should be avoided or converted to energy more in the
future in order to reduce environmental problems and provide additional sources of energy. In this
aspect, biogas plant is an effective option where gas is produced biologically by the fermentation of
animal dungs, sewage, and agricultural residues. To utilize biogas as a transportation fuel, raw biogas has
to undergo two major processes: cleaning and upgrading, to achieve natural gas quality. The upgraded
biogas (so called bio-methane or bio-CNG) is considered green fuel with respect to environment, climate,
and human health. However, the resulting bio-CNG from the processes still needs to be evaluated in
terms of greenhouse gas emissions and energy aspects. This paper presents the integrated life cycle
energy and environmental assessment of compressed bio-methane gas (CBG or bio-CNG) generated from
cassava starch wastewater treatment plant in Thailand. The functional units were set to be 1 MJ of bioCNG and 1 km of vehicle driven. The system boundary covered six main steps: digestion, purification and
upgrading, compression, distribution, refueling, and combustion. The energy analysis result showed that
the net energy ratio was higher than one, indicating a net energy gain. For the greenhouse gases aspect,
the results showed that the biogas production and biogas upgrading step had the highest impact due to
methane loss and high energy consumption. Comparing with other fuels, the global warming potential of
bio-CNG was lower than those of fossil-based CNG and gasoline