Borselleca, Elisabetta (2025) Design of bioprocesses for waste valorization into functional polyhydroxyalkanoates. [Tesi di dottorato]

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Abstract

Plastics are widely used due to their versatility, lightness, and low cost, but their dependence on fossil resources and poor end-of-life management raise serious environmental and health concerns. The transition towards a circular economy is promoting sustainable alternatives, including bioplastics. Among them, polyhydroxyalkanoates (PHA) are promising for their biodegradability, structural versatility, and compatibility with conventional plastic processing. However, their large-scale adoption is still limited by high production costs and performance gaps compared to fossil plastics. This thesis aimed to address these challenges through three main strategies: (i) valorization of agri-food wastes as renewable feedstocks for PHA biosynthesis, (ii) development of innovative production processes using unconventional microorganisms and simplified downstream approaches, and (iii) integration of PHA into functional applications such as bio-based adhesives and multilayer packaging. Spent coffee grounds (SCGs) were selected as a model biomass and processed through a cascade biorefinery approach, recovering multiple fractions, including polysaccharides and lipids. These were respectively converted into PHB and mcl-PHA, the latter successfully applied as a bio-based adhesive on packaging substrates. The extremophilic archaeon Haloferax mediterranei was investigated for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biosynthesis, showing advantages in high-salinity fermentations that reduce contamination risks and sterilization requirements. In parallel, a sequential downstream strategy enabled efficient recovery of both PHBV and bacterioruberin, a high-value carotenoid, highlighting the potential of extremophiles in sustainable bioprocesses. Finally, within the framework of the PRIMA project MATE4MEAT and in collaboration with Universitat Jaume I (Castellón de la Plana, Spain), a fully PHA-based multilayer packaging prototype was developed, composed of structural, adhesive and active layers. The structural layer was bonded to the active one using the SCGs-derived mcl-PHA as interlayer adhesive, while the active layer was additivated with halloysite nanotubes loaded with SCGs bioactives, displaying antioxidant and antimicrobial activity after pilot-scale extrusion. In conclusion, the thesis demonstrates how coupling PHA biosynthesis with the valorization of agri-food wastes can deliver sustainable and multifunctional materials, contributing to the transition towards a circular economy.

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