In a world facing increasing environmental and energy challenges, anaerobic digestion of agrifood by-products and food waste could contribute to the production of green energy while reducing greenhouse gas emissions into the atmosphere. Anaerobic digestion is a biological process capable of breaking down and stabilising organic matter in the absence of oxygen and converting it into a renewable source of energy, known as biogas. Biomethane production also enables the generation of electricity and produces digestate, a by-product of the digestion process that can be used as a soil conditioner or fertiliser. This review aims to highlight how substrate pretreatment, together with the optimisation of operating parameters, application of additives, recirculation of digestate and frequent feeding, can increase biogas production. An overview of the basics of the anaerobic digestion of agrifood by-products and food waste is provided, including feedstock characteristics (nutrient content, particle size and inhibitory compounds) and process parameters (process configuration, pH, temperature, total and volatile solids, total Kjeldahl nitrogen, ammonium, chemical oxygen demand, carbon/nitrogen ratio, retention time, organic loading rate, etc.). In addition, recent studies in the field of processes, equipment and pretreatments that can significantly improve the anaerobic digestion process of agricultural and food wastes were classified and discussed. Finally, the challenges and future perspectives of biogas production from the agrifood sector are addressed.

Anaerobic codigestion of olive mill wastewater for renewable energy production constitutes a promising process to overcome management and environmental issues due to their conventional disposal. The present study aims at assessing biogas and biomethane production from olive mill wastewater by performing biochemical methane potential tests. Hence, mixtures containing 0% (blank), 20% and 30% olive mill wastewater, in volume, were experimented on under mesophilic conditions. In addition, life cycle assessment and life cycle costing were performed for sustainability analysis. Particularly, life cycle assessment allowed assessing the potential environmental impact resulting from the tested process, while life cycle costing in conjunction with specific economic indicators allowed performing the economic feasibility analysis. The research highlighted reliable outcomes: higher amounts of biogas (80.22 ± 24.49 NL.kg_SV⁻¹) and methane (47.68 ± 17.55 NL.kg_SV⁻¹) were obtained when implementing a higher amount of olive mill wastewater (30%) (v/v) in the batch reactors. According to life cycle assessment, the biogas ecoprofile was better when using 20% (v/v) olive mill wastewater. Similarly, the economic results demonstrated the profitability of the process, with better performances when using 20% (v/v) olive mill wastewater. These findings confirm the advantages from using farm and food industry by-products for the production of renewable energy as well as organic fertilizers, which could be used in situ to enhance farm sustainability.

The present study analyses the transmission of vibrations generated from a multidirectional trunk shaker to olive tree structure considering both the aerial zone (trunk and branches) and the underground zone (the coarse root). The vibration characterization was conducted by measuring acceleration on several points of the tree during harvesting operations. The influence of two different heights of shaker head clamping was analysed. In addition, a dynamic probing was performed in order to evaluate soil compaction. The results showed that the vibration performed by the trunk shaker head, corresponding to an acceleration resultant of approximately 77 ms–2 with a dominant vibration frequency of 18 Hz, increased up to 106% in branches and decreased up to 90% in trunks. At root level, where the analysis was carried out at 1/3 and 2/3 of the coarse root length, the acceleration values diminished significantly to 17 ms–2 and 12 ms–2, respectively. Soil dynamic resistance was lower (36 kg cm–2) near the trees than between the trees (53 kg cm–2). The vibration transmission to the aerial and the underground parts diversely influences the dynamic behaviour of the olive tree, considering an operational frequency of a commercial trunk shaker. The assessment of vibration transmission to the aerial part could contribute to improve fruit detachment and reduce branch breaking and leaf detachment. While vibration transmission to the underground part rises new challenges considering soil compaction in olive groves.