Fermentative H2 production by an anaerobic H2-producing
mixed culture and C. butyricum was possible from dry ground S.
obliquus biomass. On the basis of model substrates corresponding
to the carbohydrates mostly found in microalgal storage compounds and cell wall polymers, LE37 was found to be the mixed
culture best adapted for H2 production. When grown with the
microalgal biomass as the only carbon and energy source, LE37
produced 34.8 mL H2/g vs with a H2 yield of 1.52 mol/mol of glucose equivalents. The co-culture of LE37 and C. butyricum increased
the H2 production and the H2 yield to 48.9 mL/g vs and 2.01 mol /
mol of glucose equivalents, respectively, but the produced biogas
presented a lower purity when compared with the pure strain.
Using S. obliquus biomass cultured under nitrogen stress to
increase the accumulation of sugars, C. butyricum attained not only
a better H2 yield of 2.74 mol/mol of glucose equivalents, but also a
superior degree of the biogas purity (H2/CO2 of 1.7). The maximum
H2 production was 116.3 mL/g vs and the highest productivity was
153.9 mL/L h within the first 24 h of incubation. Acetic and butyric
acid were produced as the predominant co-metabolites by the pure
strain. These organic acids can be converted into bioenergy vectors
or precursors for bioplastics and boost the economic feasibility of
bioH2 production.