Towards a sustainable industry with low energetic and environmental impact, based on the industrial cultivation of cyanobacteria

The aim of this PhD research project is study a feasibility investigation about the possibility of using cyanobacteria as factories for the industrial production of high value compound, namely cyanophycin. This topic was addressed from different points of view, through both laboratory experiments and mathematical modelling. Different cyanobacterial species were cultivated in batch and continuous photobioreactors at lab scale in order to study cyanophycin accumulation in the cells. The Design of Dynamic Experiments (DoDE) combined to Dynamic Response Model (DRSM) and to Response Surface Model (RSM) was applied to model the growth of Synechocystis sp. PCC 6803 and to investigate the effect of three dynamic operating variables on cyanophycin production in batch system. Then, in view of an industrial prolonged campaign, the cyanophycin production was stabilized by cultivating different cyanobacterial species in continuous flat-plate photobioreactors and assessing the effect of different operating variables on the cyanophycin productivity. Also the possibility of obtaining cyanophycin in continuous system by diazotrophic cyanobacteria was addressed, exploiting N2 as the only source of nitrogen. To further increase cyanophycin productivity an engineered strain was cultivated in continuous systems under nitrogen fixing conditions. As regards the mathematical modelling, both the nutrients uptake and the oxygen inhibition in a continuous system were accounted for. Finally, based on the results obtained at laboratory scale, a preliminary economic assessment was performed for a one-hectare cyanophycin production plant, and the total product cost was evaluated in three different scenarios.