Used oils

Used oils are liquid waste from lubricating, industrial or cooking oils that have lost their original properties and can no longer perform their initial function. Although they are generated in apparently modest volumes, they are a serious environmental problem if mismanaged: it is often cited that a single litre of used oil can contaminate a very large volume of water, on the order of a thousand litres.

What are used oils?

Used oils include all mineral, synthetic or vegetable oils that no longer meet the conditions for their intended use after being used. There are two broad categories:

1. Industrial oils and lubricants: used in engines, gearboxes, machinery and electrical transformers. They can contain heavy metals, degraded additives and hazardous hydrocarbons.
2. Cooking oils (domestic and hospitality): from frying and food processing. They lose quality and can contain food residues, oxidised fatty acids and water.

Environmental and health risks

• Water and soil pollution: uncontrolled dumping into drains or rivers forms a film that prevents water from oxygenating and disrupts wastewater treatment plants.
• Health risks: repeatedly reusing cooking oil generates toxic compounds (such as acrolein and polycyclic aromatic hydrocarbons), and contact with used industrial oils can cause irritation, chronic toxicity or carcinogenic effects.
• Fire risk: some industrial oils are highly flammable.

Applicable regulation

In Spain

• Law 7/2022 on waste and contaminated soil.
• Royal Decree 679/2006 on the management of used industrial oils.
• Municipal by-laws covering civic amenity sites and the collection of cooking oil.

In the European Union

• Directive 2008/98/EC, which sets the waste hierarchy.
• Regulation (EC) 1357/2014 on the classification of hazardous properties.
• Directive (EU) 2018/851, which strengthens the move towards a circular economy.

Treatment and recovery processes

• Regeneration of industrial oils: filtering and removing contaminants to recover base oils for new lubricants. This is the preferred route under EU law.
• Biodiesel from used vegetable oils: transesterification with methanol and catalysts produces a renewable transport fuel.
• Direct energy recovery: use as a fuel in cement kilns or industrial boilers after suitable treatment.
• Composting and co-digestion: for small quantities of vegetable oils integrated into biowaste treatment plants.

Benefits of proper management

• Environmental: reduced water and air pollution.
• Economic: creation of valuable products such as biodiesel and base oils.
• Social: regulatory compliance and a positive image for companies and municipalities.

Relationship with the circular economy

Used oils are a textbook example of the circular economy: managed correctly they avoid pollution, are converted into new products such as biodiesel and regenerated lubricants, and reduce reliance on virgin raw materials, in line with the waste hierarchy. Key future challenges include increasing the still-low collection of domestic cooking oil and improving the traceability of authorised collection.

Managing used oils well transforms a highly polluting waste into a valuable resource for energy and industry. At Manglai we help companies measure their environmental footprint and prepare their sustainability reporting. Discover how Manglai can help you.