Olive pomace valorization through a circular economy approach

Agricultural production systems worldwide are confronted with significant challenges, including the impacts of climate change, declining availability of water for irrigation, rising production costs, and a steady reduction in the agricultural workforce over recent decades. In parallel, the generation of agro-industrial residues has become an issue of growing concern due to the significant environmental and economic burdens associated with their management. For this reason, the valorisation of agri‑food waste streams, either through the recovery of high‑value bioactive molecules or through their conversion into bioenergy, has emerged as a priority research area, aimed at promoting more sustainable resource management practices and supporting the transition toward a circular economy. The PNRR CN‑Agritech Project was founded against this background, laying the foundations for an in‑depth investigation into the valorisation of agro‑industrial by‑products through innovative technologies that can be scaled up to pilot level and ultimately deployed directly on the field, thereby reducing the environmental impact associated with conventional biomass disposal strategies. This work is inserted within the framework of the PNRR CN‑Agritech project, exploring the comprehensive valorisation of olive pomace (OP), a polyphenol‑rich and highly phytotoxic by‑product of the olive oil industry. The overarching objective is to convert this agro‑industrial residue into high‑value products and renewable energy carriers by integrating advanced extraction technologies, biochemical and thermochemical conversion routes, and environmental sustainability assessment, thereby promoting circular economy strategies in the agri‑food sector. The work is articulated into six chapters. Chapter 1 provides the scientific and strategic context, outlining the goals of the Agritech project, the principles of the European Green Deal, and the state of the art on OP composition, polyphenolic fractions, extraction methodologies, biofuel production processes, agro‑industrial applications, and life cycle assessment. Chapter 2 presents an extensive experimental study on polyphenol recovery from OP through two unconventional technologies: High‑Pressure and Temperature Extraction (HPTE) and Solid–Liquid MultiVariable Extraction (SoLVE). The chapter includes physicochemical characterization of OP, extraction kinetics, HPLC qualitative and quantitative profiling, biological assays for neuronal protection and antifungal activity, and the validation of a 20‑L HPTE pilot plant for on‑site application. Chapter 3 investigates the biochemical valorisation of exhausted OP through anaerobic digestion. Various pretreatments, focusing on HPTE and alkali pretrearments, are evaluated to reduce polyphenolic inhibition, enhance biodegradability, and improve methane production. Chapter 4 examines the thermochemical valorisation of OP and digestate via pyrolysis, characterizing the distribution and chemical composition of reaction products to assess their potential for energy recovery reducing the environmental impact of these byproducts. Chapter 5 integrates the previous results into a full Life Cycle Assessment of the overall OP valorisation chain, comparing multiple extraction and scale‑up scenarios and calculating environmental and circularity indicators to identify process hotspots and sustainability gains. Finally, Chapter 6 extends the valorisation strategy to another relevant agro‑industrial residue, artichoke roots, through optimization of HPTE extraction using Response Surface Methodology, highlighting the broader applicability of the proposed technological framework. Overall, the thesis demonstrates that HPTE is a highly efficient, scalable, and environmentally favourable extraction technology capable of enabling both high‑quality polyphenol recovery and improved downstream valorisation routes such as anaerobic digestion and pyrolysis. The integrated results confirm the technical feasibility and environmental relevance of adopting a circular bioeconomy model for agri‑food residues, supported by multi‑level process optimization and life‑cycle‑based decision making.