Some 850,0000 tons of oil are consumed in Spain per year. The production of waste is proportional: about 150 million liters.


To win a dispute with Poseidon for the protection of a city, the goddess Athena made an olive tree sprout. Oil could be obtained from it to be used as food, a remedy for wounds, and anointing oil. Thanks to the virtues of the tree and its product, Athena won. Since then it has been known as the goddess of wisdom and the city received the name of Athens.

Oil appeared as a natural step after the invention of agriculture. Humanity domesticated plants – such as the olive tree, the soybean, the sunflower– and animals to extract their oils and fats, respectively, and use them both in food and in industry.

Since ancient Greece and the earliest agricultural civilizations, mankind has developed industrial production skills of these substances that would amaze Zeus himself.

In Spain, for example, we consume close to 850,0000 t of oil per year. This massive oil production is associated with a proportional waste production. The US generates about 11 billion liters of used oil, while in Europe this figure rises to 1 billion. Spain generates about 150 million liters of used vegetable oil.

Regarding the residual animal fatsIn the US alone, 2.6 million tons (beef, pork, sheep fat, etc.) were discarded.

Both substances are generated mainly from food processing industries, restaurants and in our homes.

Restaurants generate large amounts of oil waste.Marco Verch Professional Photographer Seguir/Flickr, CC BY

A polluting residue

Oil and fat residues must be disposed of separately from organic residues generated during cooking. They should never be dumped into the drainage network, since its contamination capacity is high. A landfill or mismanagement of this waste represents a real danger; It is estimated that a liter of oil can contaminate a thousand liters of water.

Due to their immiscibility, these substances create a superficial film preventing the exchange of oxygen in aquatic environments. They thus cause the degradation of rivers, lakes, aquifers and affect soils, ecosystems and, therefore, agriculture. Its persistence causes the increase in infrastructure costs necessary for the remediation of contaminated soils and water purification.

Traditionally, a homemade form of recycling has been the soap production. By combining the residual oil with caustic soda and applying heat, the saponification reaction takes place. The most daring can also produce their own fuel by producing homemade biodiesel.

However, modern life is hardly compatible with craftsmanship. Therefore, it is best to leave the recycling of this waste in specialized hands, who will carry out a controlled collection.

Some initiatives such as Madre Coraje or companies specialized in oil collection are in charge of this work. To do this, they have installed specific containers, which usually show bright colors such as orange. Used oil, previously accumulated at home in used bottles, is deposited in these containers.

The Gipuzkoan company Eko3r has taken a step forward by developing smart containers, thus improving collection efficiency.

Used oil collection container.Flickr/Gabriel Mg, CC BY-NC

A second life

The scientific community is trying to give a value to these residues, so that, through a series of transformations, they can be use for other purposes.

The reuse or recycling, which is the enhancement of this waste, is part of the circular economy model. This is done through a model of biorefinery. In these facilities, a variety of products and bioenergy are obtained from biomass (or plant or animal waste).

The process is similar to traditional refineries, but more sustainable. Opting for this alternative allows mitigate our dependence on oil, its environmental impact and reduce the impact of dumping this food waste.

The other lives of oil.Miguel Carmona, Author provided

Biofuel manufacturing

Fats and oils are substances called esters. Generally, they are made up of three fatty acids (which can have a higher degree of saturation or unsaturation) and a glycerin molecule. We call this type of ester triglyceride and its synthesis in nature is related to energy storage for times of scarcity.

Triglycerides are synthesized by bacteria, fungi, plants, animals, and humans. If at room temperature they are in a liquid state, they are oils and if they are in solid state they are fats.

The oil can be used as a fuel for diesel engines. In fact, the engine that Rudolf Diesel invented and presented in 1900 at the World’s Fair in Paris used peanut oil as fuel.

However, the viscosity of the oils is very high, which means that carbon can form when burned, among other problems. To reduce it, a transesterification reaction is used. This process basically consists of substituting the glycerin molecule for another lighter alcohol, transforming the ester into biodiesel. In this way, it is possible to reduce the viscosity and produce a fuel with properties similar to diesel.

The biodiesel has been losing weight as an alternative fuel, since its production usually starts from vegetable oils and could, therefore, compete with its use in food.

The use of residual oils You can solve this conflict, since it has been shown that the biodiesel obtained has the same quality as that from vegetable oils.

In the BIOSAHE Research Group we have produced biodiesel from different oils and fats: recycled oils, inedible vegetable oils, oils extracted from garbage and kebab fats.

On the other hand, the emergence of electric cars and other alternative fuels such as hydrogen it can further reduce the need for biodiesel, reducing its use to those situations in which no other emission-free source can be used.

Biolubricants and bioplastics

Oils and greases can also be used for lubrication. With a process similar to that of biodiesel production, new biolubricants have been obtained, which are biodegradable and less polluting than mineral oils.

In addition to applications in the automotive sector, these wastes can be used in the pharmaceutical and nutraceutical sector. The production of soaps via saponification has been a fact for a long time, but it has been observed that the composition of many of these residues is rich in antioxidants and that it can help in the treatment of many diseases.

Regarding the fish processing industry, we have found that residues are rich in omega-3 fatty acids, which have a high added value to combat, for example, cholesterol.

A use of great value to develop in the coming years is the production of bioplastics from microorganisms fed with residual oils.

Many bacteria have the ability to break down triglycerides and include them in your metabolism (Thanks to the secretion of an enzyme called lipase and a metabolic process called β-oxidation, which humans use to lose weight). Thus, they are capable of transforming them into other substances such as bioplastics.

Biopolymers have been shown to have properties similar to thermoplastics derived from petroleum. Therefore, they can be used in technology, such as 3D printing, opening an incredible range of possibilities.

As we see, the Oil that comes out of the fryer can have thousands of lives. What helped us today to cook fabulous French fries, tomorrow may be the bioplastic from the pan handle.

In turn, by disposing of this utensil, other microorganisms can use this bioplastic to produce the hydrogen that takes us to work (in a new engine that takes advantage of the reaction of hydrogen and oxygen to produce energy) and water molecules, which will irrigate the olive tree. that hundreds of years ago a goddess like Athena gave us. In this case, the miracle is the result of the circular economy.

Miguel Carmona Cabello, Researcher in the Department of Physical Chemistry and Applied Thermodynamics, University of Cordoba; Pilar Dorado, Professor in the Department of Physical Chemistry and Applied Thermodynamics, University of Cordoba and Sara Pinzi, Professor of the Department of Physical Chemistry and Applied Thermodynamics, University of Cordoba

This article was originally published on The Conversation. Read the original.