Cultivation of the cyanobacterium Arthrospira (Spirulina) platensis under phosphorus limitation for intracellular carbohydrates accumulation to produce biofuels (biogas and bioethanol)

Herein the possibility of the biomass composition manipulation of the cyanobacterium A. platensis using phosphorus nutrient supply variation was studied. It was observed that when phosphorus was in limited amounts a significant accumulation of carbohydrates occurred and increased from about 10-20% up to 60-65% on a dry basis. Experiments on the maximization of carbohydrate production showed that when minimum phosphorus of 1.85 mg P g-1 dry biomass is provided to the cultures then the biomass production is not hindered, while the carbohydrates content is in its maximum amount. The alteration of the biomass composition was found that occurs gradually in relation to the intracellular phosphorus concentration. The decrease in intracellular phosphorus concentration results to the increase of the carbohydrates content and the decrease of the protein content, while lipid content probably increases only at the minimum intracellular phosphorus concentration. The carbohydrates-enriched biomass of A. platensis was consequently used as feedstock for biomethane and bioethanol production. The increased carohydrates content improved the digestion process and resulted to an increase of the biomethane yield (203 ± 10 mlCH4 gCODinfl-1) in comparison with the control (123 ± 10 mlCH4 gCODInfl-1). Also the carbohydrates-enriched biomass was acid-thermal hydrolysed to release monomer sugars, in order to be used for ethanologenic fermentation by the yeast Saccaromyces serevisiae. Hydrolysates with 0.5N acids resulted to a bioethanol yield of about 16 %gEtOH per g of dry biomass of A. platensis. This dissertation shows that biomass of A. platensis can be produced in adequate amounts under phosphorus limitation with an increased carbohydrates content for biofuel production improvement