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Sustainable Management of Olive Mill Wastewater: Treatment or Valorisation?

By: , Posted on: July 30, 2017

Olive oil is obtained from olive fruit by mechanical procedures, whereas its production involves one of the following extraction processes: i) discontinuous (press) extraction, ii) 3-phase centrifugal extraction or iii) 2-phase centrifugal extraction. Each of these processes generates in different forms and compositions.

The traditional olive pressing and the three phases continuous systems produce three streams: olive oil, olive cake (or kernel) and olive mill wastewater (OMWW). The annual world OMWW production is estimated between 10 and 30 million m3. The discontinuous process (not used often anymore) produces less but more concentrated wastewater (0.5–1m3 per 1000 kg) than the centrifugation process (1–1.5m3 per 1000 kg). The 2-phase centrifugal system was introduced during the 1990s in which the olive paste is separated into phases of olive oil and wet pomace (sludge by-product) that enables reduction of the volume of OMWW. Wet olive pomace is usually further extracted with n-hexane yielding olive cake oil, although it has no significant value because of the required energy for the drying process.

OMWW is a dark-colored, acidic (3< pH value <5.9) suspension of three phases: water, oil and solids (smashed particles of olive paste and kernel). It has a characteristic unpleasant odour and high organic content, whereas is claimed to be one of the most polluting waste produced by the agro-food industries. Typically OMWW consists of: 83-94% water, 0.4-2.5% mineral salts, 0.03–1.1% lipids and 4-16% organic compounds such as carbohydrates (2-8 g/100 g), pectin, mucilage, lignin and tannins.

Like all food processing wastes, OMWW has long been considered as a matter of treatment, minimization and prevention due to the environmental effects induced by their disposal. Most of depolluting treatments of OMWW aim at the destruction of organic matter and phenolic compounds, hence the reduction of chemical oxygen demand and phytotoxicity, respectively. However, the difficulties of OMWW treatment are mainly related to:

  1. its high organic loading,
  2. seasonal operation,
  3. high territorial scattering and
  4. the presence of non-biodegradable organic compounds like long-chain fatty acids and phenols.

Many different processes have been suggested to treat OMWW, namely lagooning or direct watering on fields, co-composting, physicochemical methods (flotation and settling, coagulation, oxidation by O3 and Fenton reagent, flocculation, filtration, sedimentation, dilution open evaporating ponds and incineration), ultrafiltration/reverse osmosis, chemical and electrochemical treatments and manufacture into animal food. Although the environmental problem is more intense for the disposal of OMWW, the above techniques are typically proposed to treat all kind of olive oil processing effluents. In an attempt to categorize the proposed methodologies of OMW management, three categories can be denoted:

  1. Waste reduction via olive production systems conversion (i.e. 2-phase instead of 3-phase continuous systems)
  2. Detoxification methods aiming at the reduction of impact of the pollution load to the recipient.
  3. Recovery or recycling of components from OMW.

Click here to learn more and download chapter 1, Olive oil production sector: environmental effects and sustainability challenges, for free.

For Mediterranean countries disposal of OMWW is considered a major environmental problem. The uncontrolled disposal of OMWW on soil causes strong phytotoxic and antimicrobial effects, increases soil hydrophobicity, decreases water retention and infiltration rate, as well as affects acidity, salinity, nitrogen immobilization, microbial activity, nutrient leaching, lipids concentration, organic acids and naturally occurred phenols. At the moment there is no European Union legislation regulating OMWW management. Preconditions for safe disposal, threshold values for receptors and wastes to be disposed as well as physicochemical parameters for treated wastes are left to be set by the Member States, individually. Among European Member States, Italy, Portugal and recently Spain have put in force specific legislation for disposal/application of OMWW on agricultural soil. Furthermore, the issue of whether pomace should be considered as “waste” has been addressed in Italy and Portugal and has been resolved; it is not considered as hazardous waste. In the other olive oil producing countries, no specific legislation exists. In the following, brief analysis is provided on the specific issue of OMWW regulations in Italy, Greece and Spain as well as in Portugal and Cyprus. The latter cases have some interest as they are olive oil producing countries and have special provisions on this kind of waste.

Despite the overabundance of scientific researches aimed to increase the quality of olive oil and the efficiency of extraction systems the industrial sector showed little predispositions toward the possibility of transforming the findings of the researchers into innovative plants. Indeed, the entire olive milling process has changed very little over the last decades. The introduction of the horizontal centrifuge (decanter), coupled with the malaxation process, and has been the last big revolution in the technology field. However, the innovation transferred the problem to a new king of wastes without creating a real solution for the classical OMWW.

Many solutions have been suggested for the valorization of OMWW but many factors should be considered when selecting the best valorization method including total amount of effluents, investment costs, available land, industrial or agronomic environment, local laws and most important needs. There is not a unique, sustainable solution.

Sustainability depends on the specific needs of the local area and each olive oil industry separately. The majority of olive oil producer countries in the Mediterranean area suffer from desertification, so the water and organic matter reuse would be beneficial to improve soil fertility and control the erosion processes. Also in organic agriculture, the use of OMWW as fertilizer and/or biopesticides could represent an important source of nutrients, protecting crops and closing the cycle of residues–resources.

However, phenols of OMWW are too valuable to be diminished or discharged to the environment. Therefore, the recovery of phenols accompanied with their reutilization in different products and markets should come first. To conclude, the selection of the most suitable valorization strategy depends on the social, agricultural or industrial environment of the olive oil production plants, but more importantly to the long-term sustainability of the provided solution. Solutions that promise the total treatment of OMWW and at the same time collapse financially olive oil industries have been rejected in practice, not only because of sector’s denial, but also because of society’s tolerance that delays the enforcement of environmental legislations implementation.

Click here to learn more and download chapter 1, Olive oil production sector: environmental effects and sustainability challenges, for free.

olive mill waste

Olive Mill Waste: Recent Advances for Sustainable Management addresses today’s most relevant topics in olive oil industry sustainable management. Emphasizing recent advisable practices, the book explores the potential of reutilizing OMW to power the mill itself, the reuse of OMW as soil amendment, aerobic biological treatment of OMW and compost production, the case study of OMW within the biorefinery concept, the recovery of bioactive compounds from OMW, and their applications in food products and cosmetics.

Recent research efforts have concluded that the successful management of OMW focuses on three main routes: (a) reuse of water, (b) reuse of polyphenols, and (c) reuse of nutrients. Following this consideration, the book covers sustainable practices in the olive oil industry, revealing opportunities for reutilizing the water of OMW within the process or as s soil amendment.

At the same time, it explores all the possibilities of recovering polyphenols and reutilizing them in target products, such as foods and cosmetics. In addition, the book presents successful cases of industrial OMW valorization through real world experiences.

Key Features

  • Covers the most recent advances in the field of olive mill waste management following sustainability principles
  • Fills the gap of transfer knowledge between academia and industry
  • Explores the advantages, disadvantages and real potential of processes and products in the market

About the Author

charis galanakisCharis M. Galanakis is an interdisciplinary scientist with a fast-expanding work that balances between food and environment, industry, and academia. His research targets mainly the separation and recovery of functional macro- and micromolecules from different food by-products, as well as their implementation as additives in food and other products. He is the research and innovation director of Galanakis Laboratories (Chania, Greece) and the coordinator of Food Waste Recovery Group of ISEKI Food Association (Vienna, Austria). He serves as an editorial board member and subject editor of Food and Bioproducts Processing and Food Research International, and he has edited 6 books from Academic Press: Food Waste Recovery: Processing Technologies and Industrial Techniques (2015)Innovation Strategies in the Food Industry: Tools for implementation (2016) and Nutraceutical and Functional Food Components: Effects of Innovative Processing Techniques (2017), Olive Mill Waste: Recent advances for the Sustainable Management (2017), Handbook of Grape Processing By-Products: Sustainable Solutions (2017) and Handbook of Coffee Processing By-Products: Sustainable Applications (2017).

See his full portfolio of books here.

Follow Dr. Galanakis via Twitter – @CharisGalanakisLinkedIn or ResearchGate.

Join the Food Waste Recovery Group on LinkedIn or the Food Waste Recovery Page on Facebook.

Charis’ latest books are available to order on the Elsevier Store. Use discount code STC317 at checkout and save up to 30% on your very own copy!


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