Development of Biorefinery Schemes for the Valorization of Agro-Industrial Wastes: Production of Polyhydroxyalkanoates

Aiming to reduce the cost of production of polyhydroxyalkanoates (PHAs), it was verified the use of two agro-industrial wastes as alternatives carbon sources for the production of: A- poly(hydroxybutyrate-co-hydroxyvalerate), from olive mill wastewater (2012 campaign; 60% dephenolised). It was possible to used up to 25% v/v in the culture media due to the presence of polyphenolic inhibitors in the matrix. B- polyhydroxybutyrate (PHB) with OMW belonging to 2013 (>70% dephenolised): the culture medium could contain 100% v/v without causing inhibition. An integrated biorefinery scheme was defined and tested sequentially: polyphenols recovery, organic acids PHAs and biogas production. C- PHB from dephenolised and fermented grape pomace. An integrated biorefinery scheme was proposed for the first time for the valorisation of grape pomace. D- medium chain length polyhydroxyalkanoates by performing the anaerobic acidogenic digestion of GP before dephenolisation. From the research work on OMW, a study about total polyphenols determination by colorimetric method was carried out. Indeed, solid phase extraction break-through curves obtained during polyphenols recovery experiment were employed as a tool for the analysis. To increase the volatile fatty acids (VFAs) concentration, for obtaining a feeding solution which allow fed-batch fermentation, it was proposed to concentrate VFAs produced in acidogenic digestion using nanofiltration (NF). A preliminary feasibility study has been carried out, getting rejections in the range 30-90%, using a plant-counter and prepared in the laboratory of VFAS solution (C2 to C6) salts and buffers in distilled water. The optimization of the PHAs downstream process was also studied. It is been developed a procedure for the extraction of PHAs by cell pretreatment with, heat, acids, digestion with NaOH and ethanol-water washing. In this study it was verified that the implementation of a pre-treatment with H2SO4 allows to recover 85% of PHAs products reaching a purity of >95%.