Biogas Potential of the Side Streams Obtained in a Novel Phenolic Extraction System from Olive Mill Solid Waste.

África Fernández-Prior,Antonio Serrano,Ángeles Trujillo-Reyes,Fernando G Fermoso,Claudio Reinhard,Guillermo Rodríguez-Gutiérrez

doi:10.3390/molecules25225438

Abstract

The olive oil production is an important industrial sector in many Mediterranean areas, but it is currently struggled by the necessity of a proper valorisation of the olive mill solid waste or alperujo. The alperujo is the main by-product generated during the two-phase olive oil extraction, accounting for up to 80% of the initial olive mass. The alperujo is a source of valuable compounds, such as the pomace olive oil or highly interesting phenolic compounds. In the present research, a novel biorefinery approach has been used for phenolic compounds recovery. However, the extraction of these valuables compounds generates different exhausted phases with high organic matter content that are required to be managed. This study consists of the evaluation of the anaerobic biodegradability of the different fractions obtained in a novel biorefinery approach for the integral valorisation of alperujo. The results show that the different phases obtained during the biorefinery of the alperujo can be effectively subjected to anaerobic digestion and no inhibition processes were detected. The highest methane yield coefficients were obtained for the phases obtained after a two-months storages, i.e., suspended solids and liquid phase free of suspended solids, which generated 366 ± 7 mL CH4/g VS and 358 ± 6 mL CH4/g VS, respectively. The phenol extraction process reduced the methane yield coefficient around 25% due to the retention of biodegradable compounds during the extraction process. Regardless of this drop, the anaerobic digestion is a suitable technology for the stabilization of the different generated residual phases, whereas the high market price of the extracted phenols can largely compensate the slight decrease in the methane generation.

Highlights

Olive oil production is responsible for large amounts of agricultural by-products generally considered as waste to be disposed of
It is worth to note that the liquid phases, i.e., LPF and de-phenolized liquid phase (DLP), presented a lower volatile solid (VS)/total solids (TS) ratio than the solid phases, i.e., SP and solids phase (SS), which reached values higher than 90%
This fact would mean that most of the mineral solids (MS) would correspond to dissolved salts such as carbonates or cations such as potassium, which is an important element in the alperujo [9]

Summary

Introduction

Olive oil production is responsible for large amounts of agricultural by-products generally considered as waste to be disposed of. The most common practice for dealing with olive mill solid waste is its storage in large evaporation ponds in order to reduce its water content by natural evaporation, resulting in a thickened sludge which is either completely dried and chemically extracted (pomace oil production) or directly disposed of in landfills. This practice causes several problems such as intensive land use, bad odour, GHG emission, soil and water contamination due to leakages, insect proliferation and a high energy demand for drying the pomace in pomace oil extraction plants [3]. Current practices do not make use of the valuable properties of olive mill solid waste such as its high content in antioxidants

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Conclusion