OTTIMIZZAZIONE DELLA COLTIVAZIONE DI MICROALGHE IN FOTOBIOREATTORI IN CONTINUO PER LA PRODUZIONE DI BIOSTIMOLANTI DA IDROLIZZATI PROTEICI DI BIOMASSA MICROALGALE: DAL LABORATORIO ALLA SCALA PILOTA

This thesis work is aimed to investigate microalgae cultivation in systems suitable for up-scaling, for the production of microalgae derived biostimulants. Different microalgae species were cultivated in continuously operated photobioreactors at lab scale in order to maximize microalgal biomass productivity and photosynthetic efficiency. Several light supply approaches were investigated, utilizing artificial light with wavelengths selectively used by microalgae. Both monochromatic and multiwavelengths light emitting diodes were employed, aiming to optimize light quality in artificial illumination of photobioreactors and increasing overall photoconversion efficiency. In addition, light was supplied in continuous and flashing regime to investigate if biomass productivity and process efficiency can be enhanced by increasing light penetration in the photobioreactor. Furthermore, photobioreactors were coupled with photovoltaics, to assess if the simultaneous production of electricity and biomass can be beneficial for the microalgae production efficiency. The enzymatic hydrolysis was investigated as a downstream process, in order to develop a mild biomass treatment for the recovery of bioactive molecules. The biostimulation activity of the whole biomass as well as of the extract was tested in vitro through hormone-like bioassays. Finally, considering the results obtained from biomass cultivation and biostimulation, a pilot scale plant was designed, to develop a production process suitable for good quality biomass cultivation for biostimulants production. The pilot plant was then constructed and operated in continuous for three months, collecting productivity data at steady state. In conclusion, the possible applications of microalgae as biofertilizer and biostimulant were evaluated, taking into account the costs of biomass production in a 1-ha outdoor plant.