Algae may be split into two groups: micro-algae and macro-algae.
Both algae types were investigated as potential fuel sources
during the oil crises of the 1970s in Japan and the USA (NREL,
1998). However over the last 15 years research is dominated by
micro-algae biodiesel (Singh et al., 2011) whilst research on digestion
of digestion of micro-algae is very limited partly due to the
poor returns in biomethane production (Mata et al., 2009).