Scientists succeed in producing ethanol from highly polluting olive mill wastewater

Scientists from the Department of Biotechnology and Biological Sciences, at the Faculty of Science of the Hashemite University in Jordan have succeeded in pretreating olive mill wastewater by means of enzymes found in a fungus, in such a way that it becomes a promising substrate for the production of bioethanol.

Highly polluting olive mill wastewater (OMW) generated by the olive oil extraction process is the main waste product of this large industry. Approximately 54 billion liters of OMW are produced annually worldwide with the majority of it being produced in the Mediterranean basin.

The uncontrolled disposal of OMW is becoming a serious environmental problem, due to its high organic chemical oxygen demand (COD) concentration, and because of its high content of microbial growth-inhibiting compounds, such as phenolic compounds and tannins. The improper disposal of OMW to the environment or to domestic wastewater treatment plants is prohibited due to its toxicity to microorganisms, and also because of its potential threat to surface and groundwater. However, due to the current lack of appropriate alternative technologies to properly treat OMW, most of the wastewater in the Mediterranean area is discharged directly into sewer systems and water streams or concentrated in evaportation ponds where it degrades and releases greenhouse gas emissions.

M. I. Massadeh N. Modallal from Jordan's Hashemite University found OMW can be upgraded by removing or reducing its phenolic compounds after which its carbohydrate fraction can be used as a substrate to produce biofuels. They report their findings in this week's issue of Energy & Fuels.

Phenolic compounds can be degraded by a few microorganisms, such as white-rot fungi, which produce a variety of enzymes that are capable of oxidizing phenols. The scientists investigated the capability of Pleurotus sajor-caju (often used in mycoremediation solutions) to degrade phenols of OMW preconditioned by different treatments, namely, thermally processing (at 100 °C) diluted and undiluted OMW and thermally processing pretreated OMW with hydrogen peroxide:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: olive oil :: wastewater :: pollution :: bioremediation :: fungus :: ethanol ::

Results showed that the fungi removed phenolic compounds from OMW cultures, under all different conditions examined. The degradation of phenols reached up to 68% for the thermally processed OMW, 50% for the diluted OMW, 53% for the thermally processed OMW treated with hydrogen peroxide, and 58% for the thermally processed undiluted OMW.

The impact of such biological conversion upon lowering the phenols content of OMW was tested by yeast fermentation of the product to produce ethanol because yeast cells are very sensitive to a high phenol concentration.

Ethanol production was enhanced by the pretreatment of OMW with Pleurotus sajor-caju. The maximum ethanol production of 14.2 g/L was obtained after 48 hours of yeast fermentation using 50% diluted OMW that was thermally processed and pretreated with the microorganism.

According to the results obtained, bioconverted OMW by Pleurotus sajor-caju is a promising substrate for the bioethanol production process, with additional benefits of its use with regard to environmental and economical aspects.

Approximately, 1.8 million tons of olive oil are produced annually worldwide where the majority (98%) of it is produced in the Mediterranean basin. If the 54 billion liters of OMW resulting from this industry were to be converted into ethanol using the new method, some 650 million liters of bioethanol could be produced, while solving a major environmental problem.

References:
M. I. Massadeh and N. Modallal, "Ethanol Production from Olive Mill Wastewater (OMW) Pretreated with Pleurotus sajor-caju", Energy & Fuels, ASAP Article, October 5, 2007, doi: 10.1021/ef7004145

Basheer Sobhi, Sabbah Isam, Yazbek Ahmad, Haj Jacob, Saleeba
Ahlam, "Reducing the Environmental Impact of Olive Mill Wastewater in Jordan, Palestine and Israel" [*.pdf], R&D Center, the Galilee Society.