Life cycle assessment of biohydrogen and biomethane production and utilisation as a vehicle fuel.

Environmental burdens for the production and utilisation of biomethane vehicle fuel or a biohydrogen / biomethane blend produced from food waste or wheat feed, based on data from two different laboratory experiments, have been compared. For food waste treated by batch processes the two stage system gave high hydrogen yields (84.2 l H2 kg-1 VS added) but a lower overall energy output than the single stage system. Reduction in environmental burdens compared with diesel was achieved, supported by diversion of waste from landfill. For wheat feed, the semi continuously fed, two stage process gave low hydrogen yields (7.5 l H2 kg-1 VS added) but higher overall energy output. The process delivers reduction in fossil fuel burdens, and improvements in process efficiencies will lead to reduction in CO2 burdens compared with diesel. The study highlights the importance of understanding and optimising biofuel production parameters according to the feedstock utilised.