Researchers Convert Olive Mill Wastewater for Practical Uses

Research has discovered how to reduce the detrimental effect of olive oil mill wastewater on the environment.

Oct. 12, 2017
By Mary West

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Olive oil is prized for its culi­nary uses and health ben­e­fits around the world. Yet the process of pro­duc­ing the oil results in copi­ous amounts of waste­water, which reduces soil fer­til­ity, con­t­a­m­i­nates water­ways and harms sur­round­ing ecosystems.
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Now, sci­en­tists have found a way to trans­form some of these neg­a­tives into pos­i­tives. They have devel­oped a pro­ce­dure that changes the pol­lu­tant into use­ful prod­ucts; namely, biofer­til­iz­ers, green fuels and safe water for crop irrigation.

The objec­tive is to use local resources in a sim­ple way in order to develop a cir­cu­lar econ­omy.- Jeguirim, Mulhouse Institute of Materials Science

In the olive oil man­u­fac­tur­ing process, olives are crushed and mixed with water. Afterwards, the oil is extracted and the dirty waste­water is dis­carded. Most olive oil is pro­duced in Mediterranean coun­tries, where the milling pro­ce­dure gen­er­ates approx­i­mately 8 bil­lion gal­lons of waste­water per year. Such vast amounts present a chal­lenge in its disposal. 

The removal of the waste­water can be prob­lem­atic. Discarding it in streams can pol­lute drink­ing water and pose a haz­ard to aquatic life. Using it in crops can be detri­men­tal to the soil and effect har­vest yields. Scientists have tried burn­ing the waste­water with other wastes, but the process has been either too expen­sive or has cre­ated unac­cept­able amounts of air pollution. 

In a new study, Mejdi Jeguirim and col­leagues won­dered if they could change olive mill waste­water (OMW) into prac­ti­cal sus­tain­able prod­ucts. They com­bined OMW with cypress saw­dust, another waste prod­uct com­mon in the Mediterranean area. After quickly dry­ing the mix­ture, they col­lected the evap­o­rated water, which could safely be used for crop irrigation. 

The team then sub­jected the solid part of the mix­ture to pyrol­y­sis, which is the appli­ca­tion of high heat with­out oxy­gen to organic mate­r­ial. In the absence of oxy­gen, com­bus­tion doesn’t occur in the mate­r­ial; how­ever, it decom­poses into char­coal and com­bustible gases. The sci­en­tists col­lected the gas and con­densed it into bio-oil, a fuel that could serve as a heat source for dry­ing the OMW-saw­dust mix­ture and con­duct­ing pyrolysis. 

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Lastly, they col­lected the char­coal, which was a rich source of potas­sium, nitro­gen, phos­pho­rus and other nutri­ents. After using this for five weeks as a biofer­til­izer for plants in flow­er­pots, they observed it sig­nif­i­cantly enhanced plant growth, result­ing in larger leaves and greater yields. 

This project offers the pos­si­bil­ity of man­ag­ing olive oil mill waste­water as a source of nutri­ents for plants,” said Jeguirim, of France’s Mulhouse Institute of Materials Science. The objec­tive is to use local resources in a sim­ple way in order to develop a cir­cu­lar econ­omy. The main ben­e­fits come from the envi­ron­men­tal impact which is low­ered, and also the pro­duc­tion of a biofertilizer.” 

The study was pub­lished in the jour­nal ACS Sustainable Chemistry & Engineering.



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