Anaerobic Co-Digestion of Sewage Sludge and Organic Solid By-Products from Table Olive Processing: Influence of Substrate Mixtures on Overall Process Performance

Encarnación Díaz-Domínguez, José Ángel Rubio, James Lyng, Enrique Toro, Fernando Estévez and José L. García-Morales ()
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Encarnación Díaz-Domínguez: Department of Environmental Technologies, Faculty of Marine and Environmental Sciences, IVAGRO-Wine and Agrifood Research Institute, University of Cadiz, 11510 Cadiz, Spain
José Ángel Rubio: Department of Environmental Technologies, Faculty of Marine and Environmental Sciences, IVAGRO-Wine and Agrifood Research Institute, University of Cadiz, 11510 Cadiz, Spain
James Lyng: School of Agriculture and Food Science, University College Dublin, D04 C1P1 Dublin, Ireland
Enrique Toro: Empresa Metropolitana de Abastecimiento y Saneamiento de Aguas de Sevilla S.A. (EMASESA), C/Escuelas Pías, 41003 Sevilla, Spain
Fernando Estévez: Empresa Metropolitana de Abastecimiento y Saneamiento de Aguas de Sevilla S.A. (EMASESA), C/Escuelas Pías, 41003 Sevilla, Spain
José L. García-Morales: Department of Environmental Technologies, Faculty of Marine and Environmental Sciences, IVAGRO-Wine and Agrifood Research Institute, University of Cadiz, 11510 Cadiz, Spain

Energies, 2025, vol. 18, issue 14, 1-19

Abstract: Sewage sludge, characterized by its high organic matter and nutrient content, as well as the presence of microbial pathogens and other contaminants, requires proper management due to its significant generation rate. The table olive sector, which is highly significant in Spain as a global leader in production and export, generates various waste streams such the Organic Solid By-Products from Table Olive Processing (OSBTOP), which are mainly derived from the olive pit after the pitting process. The main aim of this study was to enhance the methane production performance of sewage sludge through co-digestion with OSBTOP as a co-substrate. Batch assays demonstrated that employing OSBTOP as a co-substrate increased methane content by 35–41% across all tested mixtures. While the highest methane yield was produced at a 40:60 (sludge:OSBTOP) ratio, a 60:40 mixture proved to be a more advantageous option for scale-up and practical application. This is attributed to factors such as the higher availability of sludge and its inherent buffering capacity, which counteracts the accumulation of volatile fatty acids and promotes process stability, thereby contributing to the study’s objective of significantly enhancing methane production from sewage sludge through co-digestion. In semi-continuous operation, methane yields in the co-digestion scenario exceeded those of mixed sludge digestion, showing a yield of 180 versus 120 LCH 4 −1 · kgVS added −1 , representing a 50% improvement. This study highlights the potential of anaerobic digestion as a strategy for valorizing OSBTOP, a by-product with no prior studies, while demonstrating that its co-digestion with sewage sludge enhances methane generation, offering a sustainable approach to organic waste treatment.

Keywords: biosolids; co-substrates; mesophilic digestion and biogas (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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