TUOMISTO, H. L., and J. HELENIUS. “Comparison of Energy and Greenhouse Gas Balances of Biogas With Other Transport Biofuel Options Based on Domestic Agricultural Biomass in Finland”. Agricultural and Food Science 17, no. 3 (January 3, 2008): 240-251. Accessed August 22, 2019. https://journal.fi/afs/article/view/5916.