Olive Mill Wastes in the Mediterranean: An Initial Assessment of Organic Matter and Nutrients of Agricultural Value

Olive mill wastes in the Mediterranean continue to be a management challenge due to the large volumes produced. Their recycling in agricultural systems may be improved, with multiple benefits for the environment and soil protection, while promoting the circular economy. Information on amounts and physicochemical properties of olive mill wastes will help the development of sustainable strategies to convert them into fertilizers or soil amendments in the Mediterranean Basin. To this end, we obtained up-to-date data on olive production and generation of wastes in Spain, Tunisia, and Greece and characterized representative samples in the laboratory in terms of their agronomic properties. We then made calculations of the total quantities of nutrients and matter which may be recycled in agriculture. More particularly, annual mineral ash contained in the waste streams of the three countries amounts to 137 thousand tons per year. Solid waste properties were more homogenous than wastewater properties, indicating that local management and production conditions in three-phase mills is more diverse, so standardization of conversion technologies is likely to be easier for two-phase mills.