Sustainable Uses for Two-Phase Olive Mill Waste

Sustainable Uses for Two-Phase Olive Mill Waste


8/11/21:   Currently around 3.2 million tonnes of olive oil is produced annually in the world ( leading to the generation of large amounts of olive oil production waste.  Spain is the largest producer of olive oil in the world accounting for 69% of total global production.

In the early 1980’s the introduction of three-phase production was considered a new era in olive oil processing technologies and considered as a newer, cleaner, and more efficient system was developed in place of the traditional press.  In the 1990’s again a new and rather innovative two-phase centrifugation system for olive oil extraction quickly replaced the three-phase system and resulted in even higher quality olive oils.  

This revolutionary olive oil extraction system certainly had its advantages. Production of olive oil at say 20% meant production of waste was being produced at around 80% and in a short space of time throughout the harvest season. This new waste is called ‘two-phase olive mill waste’ (TPOMW), ‘‘alperujo’’. In Spain, around 4 million tonnes of TPOMW is generated annually (FAOSTAT, 2012), causing serious management problems due to the phytotoxicity and slurry texture of the TPOMW.

Spanish researchers from Venta del Llano del Instituto Andaluz in Jaen looked at the possible applications for two-phase olive mill waste and the potential negative effects on olive oil quality and yield.  Researchers also compared the compost addition from mill waste with mineral fertilisation and sustainability.

The olive husk was separated in the three-phase extraction system and underwent a second oil extraction with solvents after its drying.  However, when TPOMW was treated similarly, significant difficulties appeared due to its high moisture and low fat contents. The TPOMW waste required a drying process before the second oil extraction which significantly increased production cost due to the increased demand of energy and higher temperatures which degraded oil quality.

Different technologies have been proposed for TPOMW treatment based on:- 

- evaporation ponds 

- thermal concentration 

- phenolic components extraction and its application to agricultural soils to enhance the absorption of herbicides and insecticides

With sustainable practices, reducing environmental pollution, and investing in nature-based solutions on the rise, along with current targets of net-zero carbon emissions target by 2050 in other energy sectors, the olive industry certainly has its advantages here with 10.85kg of CO2 captured for every litre of olive oil produced.  Sustainability practices are widespread in the olive industry.

In terms of olive oil production waste, composting as a method for preparing organic fertilizers and preparation is economically and ecologically sound and may well represent an acceptable sustainable solution in heading towards more nature-based solutions for the usage of TPOMW.

The physicochemical characteristics of TPOMW are adequate to be used in agriculture as an organic input, such as a slightly acidic pH (4.8–5.6), an intermediate level of Nitrogen, mainly organic, and also a significant quantity of other plant nutrients such as Potassium, Phosphorus, Calcium, Magnesium, and Iron.

An important feature of olive mill wastes is the high potassium concentration as this element is absorbed in large amounts by olive trees and is the most abundant nutrient in olive fruits.  

Another important advantage of this olive mill waste is the high organic matter concentration free of heavy metals and other potential pollutants being potentially a cleaner input option for producers.

Researchers noted  “All the composts used in this experiment presented a balanced amount of mineral which supplied the nutrient required for the good development of the plant. The amended soils had a higher content of N, P, K, and organic matter than the soil with inorganic fertilizer. The increase in soil fertility of the compost amended soils produced a significant increase in the olive oil content of the fruits, maintaining similar composition and quality of olive oil as the control. Composting TPOMW with agricultural wastes can be an environmentally friendly solution to the disposal problem of these wastes and an adequate low-cost strategy for the recycling of olive oil by-products”.

This research is interesting because it shows how producers can implement more sustainable practices in their overall production, enhance olive tree cropping, maximise yield, and potentially lower costs of total inputs.

Application of compost of two-phase olive mill waste on olive grove: Effects on soil, olive fruit and olive oil quality 


Composting is a method for preparing organic fertilizers that represents a suitable management option for the recycling of two-phase olive mill waste (TPOMW) in agriculture. Four different composts were prepared by mixing TPOMW with different agro-industrial by-products (olive pruning, sheep manure and horse manure), which were used either as bulking agents or as N sources. The mature composts were added during six consecutive years to a typical ‘Picual’ olive tree grove in the Jaén province (Spain). The effects of compost addition on soil characteristics, crop yield and nutritional status and also the quality of the olive oil were evaluated at the end of the experiment and compared to a control treated only with mineral fertilization. The most important effects on soil characteristics included a significant increase in the availability of N, P, K and an increase of soil organic matter content. The application of TPOMW compost produced a significant increase in olive oil content in the fruit. The compost amended plots had a 15% higher olive oil content than those treated with inorganic fertilization. These organics amendments maintained the composition and quality of the olive oil.

Authors:   Antonia Fernández-Hernández a,⇑ , Asunción Roig b , Nuria Serramiá b , Concepción García-Ortiz Civantos a , Miguel A. Sánchez-Monedero b

- a Centro ‘Venta del Llano’ del Instituto Andaluz de Investigación y Formación Agraria, Pesquera, Agroalimentaria y de la Producción Ecológica, Mengíbar, Jaén, Spain  

- b Department of Soil and Water Conservation and Organic Waste Management, CEBAS – CSIC, Murcia, Spain