The biogas leaving the reactor contains carbon dioxide and a
number of unwanted elements such as sulphur compounds that
need to be removed before injection into the natural gas grid. Process
energy (3% of the energy content of the cleaned biogas) was
supplied by combustion on-site of biogas (Persson, 2003). Losses
of methane to atmosphere from the cleaning and upgrading was
set to 1% of the methane produced (Persson, 2003).