Abstract
Biofuel can be generated by different organisms using various substrates. The green alga Chlorococcum humicola
OQ934050 exhibited the capability to photosynthesize carbonate carbon, maybe via the activity of carbonic anhydrase
enzymes. The optimum treatment is C:N ratio of 1:1 (0.2 mmoles sodium carbonate and 0.2 mmoles sodium
nitrate) as it induced the highest dry mass (more than 0.5 mg.mL−1). At this combination, biomass were about 0.2 mg/
mL−1 carbohydrates, 0.085 mg/mL−1 proteins, and 0.16 mg/mL−1 oil of this dry weight. The C/N ratios of 1:1 or 10:1
induced up to 30% of the Chlorococcum humicola dry mass as oils. Growth and dry matter content were hindered
at 50:1 C/N and oil content was reduced as a result. The fatty acid profile was strongly altered by the applied C.N
ratios. The defatted leftovers of the grown alga, after oil extraction, were fermented by a newly isolated heterotrophic
bacterium, identified as Bacillus coagulans OQ053202, to evolve hydrogen content as gas. The highest cumulative
hydrogen production and reducing sugar (70 ml H2/
g biomass and 0.128 mg/ml; respectively) were found at the C/N
ratio of 10:1 with the highest hydrogen evolution efficiency (HEE) of 22.8 ml H2/
mg reducing sugar. The optimum
treatment applied to the Chlorococcum humicola is C:N ratio of 1:1 for the highest dry mass, up to 30% dry mass
as oils. Some fatty acids were induced while others disappeared, depending on the C/N ratios. The highest cumulative
hydrogen production and reducing sugar were found at the C/N ratio of 10:1.