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

Abstract

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 CH4/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 O2/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 (Rmax) 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 Rmax from 87 ± 7 to 73 ± 6 mL CH4/(g VS·d).

Anaerobic Digestion of the Residue (Combination of Wastewater and Solid Waste) from a New Olive-Oil Manufacturing Process Based on an Olive Cold-Pressing System: Kinetic Approach and Process Performance

“…A mesophilic temperature of 35 ± 2 • C was selected for the experiments, which was controlled by placing the reactors in thermostatic baths under constant stirring (400 rpm). The reactors were then filled with an inoculum to a substrate (ISR) ratio of 2 (VS), reaching a final concentration of 24 g VS/L, along with a micronutrient solution [5,6]. At the outset of the experiment, nitrogen gas was flushed through the reactors for two minutes (40 mL headspace volume) with the aim of maintaining anaerobic conditions.…”

“…The Logistic model also estimates the nd the Rm together with the potential for methane production of the substrates odel has already been used for the anaerobic digestion of different organic nd for estimating methane production in leachate from landfills [9]. utput t energy output corresponding to the BMP tests was determined by using the l data according to Equation (2) [5,10]:…”

“…rgy Output e heat energy output corresponding to the BMP tests was determined by using the ental data according to Equation (2) [5,10]:…”

“…The heat energy output corresponding to the BMP tests was determined b experimental data according to Equation (2) [5,10]: ); Ɛ is the lowest heating value for methane (35,800 kJ/m 3 CH4); λm is the energy conversion factor of methane (0.9);…”

“…More recently, the use of cold pressure has been employed as a novel system that allows for increasing oil recovery yield while improving the use of its by-products, mainly alperujo (olive pomace). Previous studies have shown that the application of a cold-pressure treatment does not improve the subsequent application of anaerobic digestion (AD) of the olive pomace for the integral utilization of the by-product, although it is also possible [5]. These studies were carried out using the solid fraction obtained after olive-oil extraction with or without cold-press treatment.…”