Conversion of olive oil wastes through combined pyrolysis and anaerobic digestion: energy, value added products and eco-fertilizers production – PYRODIGEST

In Mediterranean countries, the olive industry represents a major agricultural sector, generating liquid and solid wastes (cake, stalks and wood residues) with detrimental environmental impacts (salinity, acidity and high polyphenol load). The PYRODIGEST project aims to render the olive oil industry more sustainable through a new integrated waste treatment system for the olive industry based on the principle of “industrial symbiosis”, associated with the production of high-value products. For this purpose, a hybrid energy system integrating anaerobic digestion, and pyrolysis processes will be tested and optimized, combining the production of multi-purpose energy carriers, fertilizer/amending, soil improver, and high-value products. The project provides an integrated approach for the treatment of both solid and liquid wastes from the oil industry in a circular economy concept. Solid wastes (wood, leaves, stone, pomace…) are treated through pyrolysis process, converting organic matter in syngas and bio-oil used as energy carriers, and biochar that can be used both as soil improver, or activated carbon precursor (high-value product). Liquid wastes (OMEs: Olive Mill Effluents) are treated through anaerobic digestion (AD), producing biogas as an energy carrier, and digested (stabilized) organic matter as fertilizer and soil improver. OMEs are rich in polyphenols, a strong inhibitor of AD processes, also causing environmental pollution due to its toxicity. To tackle this issue, polyphenols will be extracted prior to AD process in view of their recovery as marketable high-value product by adsorption on Activated Carbons using biochar from solid wastes pyrolysis as precursor. Subsequently, detoxified OMEs effluents will be degraded through advanced UASB (Upflow Anaerobic Sludge Blanket) technology, further optimized by the application of various biofilm supports (ceramic balls; plastics carriers and granular activated carbon). Finally, digestate and biochar generated in the hybrid system can be applied as high-value fertilizer and soil improver, reducing the industrial fertilizers use and answering the main concern of soil preservation. The synergistic application of biochar together with digestate can increase the retention of nutrients applied to the soil, thus improving plant uptake and reducing the leaching of nutrients, heavy metals and organic contaminants. Furthermore, due to its physico-chemical properties, biochar can also improve the water retention capacity and reduce soil acidity, which is of high interest for the Mediterranean agricultural soils.
The main objective of the PYRODIGEST project is to develop a hybrid energy system providing fertilizer and soil improver for the preservation soil quality, fertility and organic matter, along with high-value products for local self-sufficiency and local economic development.

The PYRODIGEST project will include seven partners in five countries (France, Turkey, Tunisia, Algeria and Morocco). Project partners will comprise universities (University of Mohammed VI; University of ORAN,Ege University), research institutes (General Directorate of Agricultural Research-Olive Research Center; Agropolymer Engineering and Emerging Technologies; Biotechnology Center of Sfax) and a private association (Association pour l'Environnement et la sécurité en Aquitaine).