The use of a variety of photosynthetic organisms has been proposed that directly or indirectly biocatalyse the splitting of water into H2 and O2 (Melis and Happe 2001; Hallenbeck and Benemann 2002; Nath and Das 2004; Hahn et al. 2007; Hankamer et al. 2007). The production of hydrogen from wastewaters or carbohydrates by H2- producing bacteria has also been proposed (Van Ginkel et al. 2005; Rupprecht et al. 2006; Wongtanet et al. 2007; Jones 2008). The latter approach to generating H2 so far has a poor conversion efficiency (Jones 2008).

Melis and Melnicki (2006) have suggested the combined production of hydrogen by H2-producing bacteria and photosynthetic algae, and Westermann et al. (2007) have proposed biorefineries producing ethanol and hydrogen. Furthermore, there have been proposals to electrolytically generate hydrogen from wastes in the pres­ence of microbes (Stams et al. 2006; Dumas et al. 2008).

The methods to produce H2 with the help of micro-organisms would often re­quire closed systems (Rupprecht et al. 2006). This is necessary for the capture and removal of H2, which may inhibit H2 production, maintain anaerobic conditions and be highly conducive to limiting infection by unwanted organisms, but limits the scope for large-scale production.