Olive Oil Mills Wastes

Characteristics and typical composition of olive oil mills wastes

Olive oil mills wastes constitutes an important pollution factor for the olive oil-producing regions but also a significant problem to be solved for the agricultural industry. The main reasons are:

  1. The large wastes amounts produced in relatively small time interval, which should, ideally, be processed or be disposed with safety for the environment before the beginning of the next productive period. Although the produced waste volumes depend on a lot of factors, as the variety of olive-crop, the stage of maturity, the storage before the processing, the time of segregation of olive oil from the crop, the available water for the processing and its cost, in general lines, for each 100 kilos of olive-crop they are produced 100-120 kilos of humid waste, while the medium daily production per mill varies between 15 and 20 tons.
  2. The physico-chemical waste characteristics; some of them may cause significant problems to the recipients, where they are disposed (e.g. eutrophication, toxic phenomena to the aquatic fauna, phytotoxicity, aesthetic degradation).
  3. The substantial high organic load, which is constituted by compounds/substances that can be easily decomposed (e.gg sugars, organic acids, amino-acids, proteins) and by substances that are decomposed with difficulty (e.g. fats, polyphenols). Wastes contain very high concentration of polyphenols, which may cause the appearance of bio-toxic phenomena in the recipients.

Olive oil mills wastes contain also a lot of inorganic components (nitrogen, phosphorous, sodium, potassium, iron, etc). Even if these inorganic components are not toxic, their relatively high concentration and the periodically repeated disposal can cause problems in the environment.

Olive oil mills wastes are characterized from:

  • Dark violet-brown to black color
  • Very intense smell of olive oil * Very high organic load (COD up to 220g/l)
  • pH values between 3 and 6
  • High electrical conductivity
  • Large concentration of polyphenolic compounds (from 0,5 to 24g/l)
  • High content in total solids

However, it should be kept in mind that as far as the composition of olive oil mills wastes is concerned, the values of their parameters given in the literature are rarely of the same value. This is because olive oil mills have seasonal operation, use different technology whereas, the crops that are processed daily are of different origin-treatment-variety. Wastes composition varies also from country to country. For example :

Parameter      Spain (Granada)        Italy (Liguria)

COD (mg/l)             49.000                      80.400

BOD5 (mg/l)             4.200                      11.500

Solids (g/l)                  35,1                         73,0

pH                               4,9                            5,2


Extraction technology and wastes' characteristics

To extract olive oil, three methods are commonly used. The traditional press method, the three-phase and the two-phase decanter centrifuge methods.

The press method is a non-continuous process, which provides high purity extra virgin olive oils.

The three-phase is a continuous process that requires the addition of warm water to improve extraction, as is the two-phase which differs by operating without adding any water. The two-phase method is the most innovative technique and produces a semi-solid cake of pressed olive fruits and stones as opposed to the highly polluting wastewater from the three-phase process. This wastewater needs treatment before disposal.

According to the 2 or 3 phase extraction system different kind of wastes are produced during the process. This scheme shows a comparison between the 2 methods.

Consequently characteristics of wastes produced according to the different extraction systems may vary depending of different factors. The tables summarize main parameters of olive wastes.

Concluding : Management of olive oil mills waste is one of the biggest problems associated with the agricultural industry. The environmental devastation caused by the accidentally or non-accidentally release of non-treated wastes that periodically occurs, is now being addressed aggressively by all major producing nations.


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  • V. Oreopoulou, W. Russ. 2007. Utilization of by-products and treatment of waste in the food industry. Springer.
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