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Purpose <p>The olive oil industry generates large amounts of olive mill wastewater and pomace characterized by high organic load and polyphenol content, which restrict their direct disposal and reuse. This study aimed to evaluate a low-cost and sustainable strategy for valorizing these residues through a sequential composting–vermicomposting process for agronomic use.</p> Methods <p>Olive mill residues were treated through an initial thermophilic composting phase lasting four months, followed by a three-month vermicomposting phase using <i>Eisenia andrei</i>. Five substrate formulations were tested: M1 (50% horse manure + 50% bedding), M2 (100% olive mill waste compost, OMWC), M3 (50% OMWC + 50% bedding), M4 (80% OMWC + 20% bedding), and M5 (90% OMWC + 10% bedding). Bedding consisted of shredded cardboard, mature compost, and dried olive leaves. Process efficiency and product quality were assessed using physicochemical, biochemical, and biological indicators, including pH, electrical conductivity, C/N ratio, total polyphenol content, humic-to-fulvic acid (HA/FA) ratio, phosphomonoesterase activities, earthworm biomass density, and phytotoxicity evaluated by <i>Lactuca sativa</i> germination assays.</p> Results <p>The formulation containing 90% compost and 10% bedding showed the highest performance, achieving an 86% reduction in total polyphenols, a decrease in the C/N ratio from 25.3 to 14.3, and an HA/FA ratio exceeding 4, indicating advanced humification. The resulting vermicompost exhibited enhanced enzymatic activity, increased earthworm reproduction, and germination index values above 200%, confirming complete detoxification and high agronomic quality. Correlation analysis highlighted strong relationships between organic matter stabilization, enzymatic activity, and earthworm biomass density.</p> Conclusion <p>Sequential composting–vermicomposting represents an effective and scalable pathway for the sustainable valorization of olive mill wastewater and pomace, supporting circular economy approaches through the production of stable, high-value organic amendments suitable for agricultural applications.</p> Graphical Abstract <p></p>

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Sustainable Valorization of Olive Mill Wastewater and Pomace by Sequential Composting–Vermicomposting for Agronomic Use

  • 期刊论文

  • 发表日期：

    2026年7月4日

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  • Hanen Zaier,
  • Walid Chmingui,
  • Amira Gannar,
  • Yassine Hidri,
  • Ajmi Larbi

摘要

Purpose

The olive oil industry generates large amounts of olive mill wastewater and pomace characterized by high organic load and polyphenol content, which restrict their direct disposal and reuse. This study aimed to evaluate a low-cost and sustainable strategy for valorizing these residues through a sequential composting–vermicomposting process for agronomic use.

Methods

Olive mill residues were treated through an initial thermophilic composting phase lasting four months, followed by a three-month vermicomposting phase using Eisenia andrei. Five substrate formulations were tested: M1 (50% horse manure + 50% bedding), M2 (100% olive mill waste compost, OMWC), M3 (50% OMWC + 50% bedding), M4 (80% OMWC + 20% bedding), and M5 (90% OMWC + 10% bedding). Bedding consisted of shredded cardboard, mature compost, and dried olive leaves. Process efficiency and product quality were assessed using physicochemical, biochemical, and biological indicators, including pH, electrical conductivity, C/N ratio, total polyphenol content, humic-to-fulvic acid (HA/FA) ratio, phosphomonoesterase activities, earthworm biomass density, and phytotoxicity evaluated by Lactuca sativa germination assays.

Results

The formulation containing 90% compost and 10% bedding showed the highest performance, achieving an 86% reduction in total polyphenols, a decrease in the C/N ratio from 25.3 to 14.3, and an HA/FA ratio exceeding 4, indicating advanced humification. The resulting vermicompost exhibited enhanced enzymatic activity, increased earthworm reproduction, and germination index values above 200%, confirming complete detoxification and high agronomic quality. Correlation analysis highlighted strong relationships between organic matter stabilization, enzymatic activity, and earthworm biomass density.

Conclusion

Sequential composting–vermicomposting represents an effective and scalable pathway for the sustainable valorization of olive mill wastewater and pomace, supporting circular economy approaches through the production of stable, high-value organic amendments suitable for agricultural applications.

Graphical Abstract