Environmental Assessment of Olive Mill Solid Waste Valorization via Anaerobic Digestion Versus Olive Pomace Oil Extraction

Bernabé Alonso-Fariñas,Giovanni Esposito,Armando Oliva,Mónica Rodríguez-Galán,Antonio Serrano,Guillermo Rodríguez-Gutiérrez,Fernando G Fermoso,Juan Francisco García-Martín

doi:10.3390/pr8050626

Abstract

Anaerobic digestion is a promising alternative to valorize agrifood wastes, which is gaining interest under an environmental sustainability overview. The present research aimed to compare anaerobic digestion with olive pomace oil extraction, by using life cycle assessment, as alternatives for the valorization of the olive mill solid waste generated in the centrifugation process with a two-outlet decanter from oil mills. In the case of olive pomace oil extraction, two cases were defined depending on the type of fuel used for drying the wet pomace before the extraction: natural gas or a fraction of the generated extracted pomace. The anaerobic digestion alternative consisted of the production of biogas from the olive mill solid waste, heat and electricity cogeneration by the combustion of the generated biogas, and composting of the anaerobic digestate. The life cycle assessment showed that anaerobic digestion was the best alternative, with a global environmental impact reduction of 88.1 and 85.9% respect to crude olive pomace oil extraction using natural gas and extracted pomace, respectively, as fuel.

Highlights

The olive oil industry represents one of the fastest-growing industrial sectors worldwide, being of great importance in the economy of countries, such as Spain, Greece, and Italy, and becoming an important industry in countries, such as Chile, South Africa, or Argentina
Soap stock is not considered as a by-product according to the results reported in [13]
This was in contrast to Olive Pomace Oil Extraction (OPOE), in which the main contributors to the credits depended on the impact category

Summary

Introduction

The olive oil industry represents one of the fastest-growing industrial sectors worldwide, being of great importance in the economy of countries, such as Spain, Greece, and Italy, and becoming an important industry in countries, such as Chile, South Africa, or Argentina. The olive mill solid waste obtained from the two-outlet decanters is transported to the pomace extraction plants to extract the crude pomace oil from them, mainly by extraction with organic solvents (technical hexane) [2]. A drying phase is necessary to reduce the moisture and volatile matter of the olive mill solid waste (between 65 and 75%) to less than 8% This drying phase involves the highest energy consumption of the whole process of pomace oil extraction, and it is normally fed by natural gas or by the resulting extracted pomace from pomace oil extraction. In Spain, this energy production at an industrial scale has been possible, thanks to government incentives for the production of electricity from biomass Notwithstanding, such incentives have been drastically reduced for running plants and have been canceled for new plants. Other challenges that pomace oil producers are facing are the fluctuation of olive mill solid waste generation and, mainly, the low commercial value of crude pomace oil [3]

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