The primary objective of this study was
focused on using as few steps of biomass pretreatment as possible
to release the microalga cellular contents, particularly starch as it
is the main storage carbohydrate, in order to minimise production
and energy costs. As such, dry biomass was only submitted to
physical grinding before being added to the fermentation medium
and submitted to autoclave sterilisation. Moreover, both the clostridial strain and the mixed cultures were chosen by their ability
to produce bioH2 directly from starch without the need of a prior
saccharification step. This strategy was already successfully
employed in the production of H2 by clostridial strains from complex feedstock containing starch, like palm oil mill effluents [38],
and from raw starch [39]. The concentration of microalgal biomass
ranged from 10 to 50 g/L and its sugar concentration is determinant for the bioconversion yield. The sugar content of the microalgal biomass achieved 18% of the total algal dry mass. This value is
in accordance with the sugar concentration range described for S.
obliquus (10–17% (w/w))