As previously stated C. butyricum achieved a more stable fermentation pattern than LE37, with simultaneously the highest H2
purity in the produced biogas. Therefore C. butyricum was selected
for the study of the H2 production kinetics from S. obliquus biomass. The microalga was grown in a 4000 L raceway open pond
structure, under nitrogen restriction in order to promote sugar
accumulation. The referred batch of S. obliquus was particularly
sugar-rich. Its average composition on a dry weight basis was
307 g/kg total sugars, 204 g/kg crude protein, 202 g/kg ash,
171 g/kg fat and 116 g/kg others (by difference) [21]. The selected
biomass load was 50 g/L, the condition with which the highest
H2 production was achieved in the optimisation assay with C.
butyricum. Fig. 3 depicts the evolution of H2 and CO2 production
and soluble sugar conversion over the time.