Valorization of Agri-Food Waste into PHA and Bioplastics: From Waste Selection to Transformation

The valorization of agri-food waste is a pivotal component in developing the circular economy, wherein waste is given a second life through various conversion technologies. This review aims to provide an overview of the current state of knowledge on the valorization of agri-food waste, with a particular focus on volatile fatty acids (VFAs) and subsequent bioplastics production. To this end, a comprehensive literature search was conducted using specialist bibliographic databases. The study primarily focuses on reviewing the biological production of PHBV (poly(3-hydroxybutyrate-co-3-hydroxyvalerate)), a type of PHA, due to its relevance as a substitute for fossil-based plastics. Significant attention has been directed toward exploring the potential of agri-food wastes, such as whey, potato peelings, and brewery bagasse, as raw materials for their transformation into a tailor-made VFA solution, rich in valeric and propionic acids. Additionally, existing operational strategies and waste co-treatments have been reviewed. The produced VFAs present multiple applications, including single-cell oils, Omega-3-rich oils, and different types of PHA. Factors influencing the bio-polymerization of VFAs to PHBV, such as the type of substrate, operating conditions (pH and retention time), and the presence of specific microorganisms, have also been reviewed. Due to its physicochemical properties, PHBV has applications in sectors such as agriculture and packaging. This review concludes that transforming agri-food waste into PHBV has the potential to integrate environmental and economic benefits within a circular bioeconomy model, fostering technological innovation and the sustainable use of waste resources.