Thermophilic Dark Fermentation of Olive Mill Wastewater in Batch Reactors: Effect of pH and Organic Loading

Konstantina Tsigkou,Natalia Sivolapenko,Michael Kornaros

doi:10.3390/app12062881

Konstantina Tsigkou, Natalia Sivolapenko + Show 1 more

Open Access

https://doi.org/10.3390/app12062881

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Journal: Applied Sciences	Publication Date: Mar 11, 2022
Citations: 7	License type: CC BY 4.0

Affiliation: Politecnico di Milano, University of Patras

Abstract

In recent decades, olive oil consumption has almost tripled worldwide. Olive oil production is linked with the production of enormous amounts of olive mill wastewater, the main by-product derived from three-phase olive mills. Due to the environmental risks of olive mill wastewater disposal, the management and valorization of the specific waste stream is of great importance. This work focuses on the thermophilic dark fermentation of olive mill wastewater in batch reactors, targeting pH optimization and the organic loading effect. A series of experiments were performed, during which the organic load of the substrate remained at 40 g/L after dilution with tap water, and the pH was tested in the range of 4.5 to 7.5. The maximum yield in terms of produced hydrogen was obtained at pH 6.0, and the yields were 0.7 mol H2/mol glucose or 0.5 L H2/Lreactor. At the same conditions, a reduction of 62% of the waste’s phenols was achieved. However, concerning the effect of organic loading at the optimized pH value (6.0), a further increase in the organic load minimized the hydrogen production, and the overall process was strongly inhibited.

Highlights

According to the International Olive Council and official data, global olive oil production ranged between 3.13 and 3.28 million metric tons from 2017/2018 to 2020/2021, and it is known that, in the last 60 years, olive oil production has tripled worldwide
Hot water, which came from the thermophilic water bath (55 ± 0.5 ◦ C), was recirculated through the double wall of the reactor in order to ensure thermophilic conditions
During the optimization of olive mill wastewater (OMW) thermophilic dark fermentation (DF) in terms of H2 and/or metabolites production, a series of batch experiments was initially performed for the pH values 4.5, production, a series of batch experiments was initially performed for the pH values 4.5, 5.0, 6.0, 7.0, and 7.5 under the organic loading of 40 g COD/L

Summary

Introduction

According to the International Olive Council and official data, global olive oil production ranged between 3.13 and 3.28 million metric tons from 2017/2018 to 2020/2021, and it is known that, in the last 60 years, olive oil production has tripled worldwide. 95% of global olive oil is produced in the Mediterranean, mainly by Spain, Italy, Greece, and Portugal, and other countries such as Tunisia, Turkey, Morocco, and Algeria have stood out [1,2]. Greece ranks third in olive oil production, cultivating olive oil trees on almost 60%. Greece holds first place in black olive production, and the largest variety of oils (compared to any other country) is cultivated in Greece. An average rate of 12% of European olive oil is produced by Greece [4], 80% of which is extra virgin [5]. As Greece’s main extraction system is still the one with the three-phase decanter, at an average rate of 82%, huge amounts of liquid wastes or olive mill wastewater (OMW) are generated annually, during the period of October to February [7]

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Conclusion