Integral Valorization of Two-Phase Olive Mill Solid Waste (OMSW) and Related Washing Waters by Anaerobic Co-digestion of OMSW and the Microalga Raphidocelis subcapitata Cultivated in These Effluents

Abstract

This study evaluates the comprehensive valorization of the byproducts derived from the two-phase olive oil elaboration process [i.e., olive washing water (OWW), olive oil washing water (OOWW), and olive mill solid waste (OMSW)] in a closed-loop process. Initially, the microalga Raphidocelis subcapitata was grown using a mixture of OWW and OOWW as the culture medium, allowing phosphate, nitrate, sugars, and soluble chemical oxygen demand removal. In a second step, the microalgal biomass grown in the mixture of washing waters was used as a co-substrate together with OMSW for an anaerobic co-digestion process. The anaerobic co-digestion of the combination of 75% OMSW−25% R. subcapitata enhanced the methane yield by 7.0 and 64.5% compared to the anaerobic digestion of the OMSW and R. subcapitata individually. This schedule of operation allowed for integration of all of the byproducts generated from the two-phase olive oil elaboration process in a full valorization system and the establishment of a circular economy concept for the olive oil industry.

Features of the microalga Raphidocelis subcapitata: physiology and applications

“…Biogas consists of a mixture containing mainly methane and carbon dioxide. A recent work showed the production of methane by anaerobic digestion of R. subcapitata biomass (used as co-substrate with olive mill solid waste) cultivated in olive oil industry effluents (Fernández-Rodríguez et al 2022 ). On the other hand, bioethanol can be obtained from the whole microalgae biomass or the lipid-free portion.…”

“…In more recent years, several works have been published reporting the role of R. subcapitata in environmental and industrial biotechnology. Examples of this are the bioremediation of industrial effluents (Ribeiro et al 2022 ; Fernández-Rodríguez et al 2022 ) and pharmaceutical compounds of emerging concern (Hom-Diaz et al 2022 ), the production of biofuels (such as third-generation biodiesel) or of compounds that can be used as natural dyes and antioxidants, or to obtain innovative functional food products (Nascimento et al 2020 ).…”

Towards a circular economy in virgin olive oil production: Valorization of the olive mill waste (OMW) “alpeorujo” through polyphenol recovery with natural deep eutectic solvents (NADESs) and vermicomposting

“…EU regulations support this policy, as OMW could represent a costly by-product (Ricelli et al, 2020). Hence, efforts have been made to reuse and recycle OMW, for example using it as a fuel in thermochemical processing to generate thermal energy and electricity (Christoforou and Fokaides, 2016), in anaerobic and co-digestion processes (Fernández-Rodríguez et al, 2022) to generate a fertilizer (Kavdir and Killi, 2008), or as a component of animal feed (Molina-Alcaide and Yáñez-Ruiz, 2008). Other procedures involve subjecting OMW to biotransformation by composting (Tortosa et al, 2012), or using it as a source of phytochemicals such as phenolic compounds, tocopherols and triterpenic acids (Nunes et al, 2018;García et al, 2008).…”

Introduction to Novel Approaches in the Valorization of Agricultural Wastes and Their Applications

“…7 The special issue ends with some descriptions of the microbial transformations of the different constituents of the extracts with two aims: first, to convert the food waste components into more bioactive and bioavailable metabolites released from the matrix to enhance their biological effects through microbial fermentations 10 and, second, to reduce organic matter and contaminants from the wastes and residues of the food processing industries, as in olive oil production, using treatments with microalgae that combine decontamination with an optimized production of methane. 11 The reviews included here clearly show that there is still a need to study the use of the waste streams produced by the food and agriculture industry to reduce the contamination and valorize the residues as critical steps in the circular economy and the sustainable production of food. New green extraction technologies and novel applications for the extracts obtained in agriculture, food, cosmetics, and medicine will be developed.…”

“…The special issue ends with some descriptions of the microbial transformations of the different constituents of the extracts with two aims: first, to convert the food waste components into more bioactive and bioavailable metabolites released from the matrix to enhance their biological effects through microbial fermentations and, second, to reduce organic matter and contaminants from the wastes and residues of the food processing industries, as in olive oil production, using treatments with microalgae that combine decontamination with an optimized production of methane …”