Integrated biorefinery process for olive pomace valorisation

Abstract

Due to the great importance of the olive sector in the Mediterranean area, it is necessary to develop an economical and environmentally friendly treatment for the valorisation of olive pomace. In the present study, an integrated valorisation scheme of two-phase olive pomace (TPOP) (main semi-solid by-product produced by twophase centrifugation oil extraction systems) was assessed, where polyphenols were previously recovered in a high-value liquid extract to facilitate the subsequent continuous anaerobic digestion of dephenolised two-phase olive pomace (DTPOP). The average polyphenol extraction rate in this study was 55\%, and the subsequent optimum methane production from DTPOP (416 +/- 82 L CH4 kg VS-1 d-1) occurred at an Organic Loading Rate (OLR) of 2.89 +/- 0.07 g VS L-1 d-1, and 24 days' Hydraulic Retention Time (HRT). Although energy production from food industry waste is not a new process, the industrial implementation and application continues to be a challenge. Hence, the present paper also reports on the economic feasibility study of an industrial-scale integrated plant to treat 8000 t TPOP y-1 from a medium-sized olive mill. The economic assessment showed that the combination of polyphenol extraction and the subsequent anaerobic digestion is an attractive treatment option. Net Present Value (NPV) and Internal Return Rate (IRR) were 1,493,234 and 12.8\%, respectively, for an extract selling price of euro680 t-1 (820 USD t-1). The sensitivity analysis concluded that variations in the selling price of polyphenol extracts and ethanol acquisition are the most significant factors that might influence the global economic viability of the integrated TPOP valorisation plant.