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.

The production of short-chain-length polyhydroxyalkanoates (scl-PHAs) from municipal solid waste-derived volatile fatty acids (VFAs) has been demonstrated. The objective of the study was to evaluate the technical feasibility of the process under real operational conditions. Moreover, the process operation was conducted without pH and temperature control to reduce potential industrial implementation barriers, i.e., by simplifying the process control and minimizing the auxiliary services available for the process. A two-step bioprocess was developed, consisting of an enrichment phase in a 20 m³ fermenter operated for 214 days and an accumulation phase carried out in a 3 m³ batch fermenter across 39 accumulation cycles. In the enrichment phase, steady-state conditions were achieved once the feast/famine ratio was lower than 0.2 h/h. Thus, the impact of environmental conditions was analyzed. It was found that the system’s response was a destabilization of the culture under sharp variations at environmental temperature, followed by an adaptation period and final recovery of the system. During the accumulation phase, the impact of chemical oxygen demand (COD) feeding rates was assessed, with a maximum scl-PHA accumulation of 59 wt.% (2.87 g/L) recorded. The extraction process was also performed at demonstrative scale using dimethyl carbonate (DMC) as the solvent, yielding a scl-PHA recovery of 92% with a purity of 90%. These results confirm the technical feasibility of producing scl-PHAs from municipal organic waste at demonstrative scale, supporting the circular bioeconomy model.