Performance and kinetic evaluation of the anaerobic digestion of olive pomace derived from a novel manufacturing process based on an olive cold-pressing system: influence of the fruit ripening level

The aim of the present research was to investigate the influence of the application of a novel cold-pressing system in olive oil manufacturing on the characteristics of olive pomace (OP) and on its valorization by anaerobic digestion (AD). Green olives and olives in veraison, both from the Picual variety, were used with the objective of assessing the effect of ripening level on the performance of the AD processes. The AD processes of these OPs were assessed in biochemical methane potential (BMP) tests. The maximum methane yield (327 ± 5 mL CH 4 /g VS) and biodegradability value (90.8%) were found for the OP derived from green olives without cold-pressing, which showed the highest soluble COD (113 g O 2 /L) and the lowest total phenolic concentration (9 g gallic acid/L). The first-order and Transference Function (TF) kinetic models were employed to evaluate the variation in methane production with time and to obtain the kinetic parameters of the anaerobic processes of the four OPs tested. The kinetic constant from the first-order model, k , did not show significant differences for the four OPs tested and ranged between 0.23 and 0.27 day −1 . The TF revealed that the values for the maximum methane production rate ( R max ) were slightly higher for the OPs derived from green olives compared to those obtained from olives in veraison. For the green olives, the cold-pressing system caused a decrease in the value of R max from 87 ± 7 to 73 ± 6 mL CH 4 /(g VS·d).