From waste to value: a green process for recycling waste cooking oils
Cooking oil is one of the most used products globally, with households and the restaurant industry depending on it for the preparation of food. In Europe alone, it is estimated that just one person goes through approximately 8 litres of cooking oil per year(opens in new window), which then becomes waste, and, consequently, a significant source of pollution. One solution to the environmental concerns raised by discarded cooking oil is its recycling; however, existing technology (except for biodiesel production) has not been able to fully support progress in this area until now. The EU-funded WORLD(opens in new window) project aimed at developing a reliable system for the valorisation of waste cooking oil (WCO) that would surpass existing limitations, opening the door to sustainable by-products. “When WORLD started, we saw that most WCO recycling was based on simple decantation and filtration. This can remove only part of the impurities, but it is not enough for real high-quality reuse of the oil in new products such as bio-lubricants,” says project coordinator Andrea Mele. “The sector had recycling, but not yet a well-designed, zero-waste, industrially robust system,” he stresses.
A clean and green process
In order for WCO to be repurposed, it first needs to be purified. For this, Alberto Mannu of the WORLD team introduced a two-step method using simple, natural means. First, WCO is washed with water under controlled temperature and pH conditions. Then, if necessary, it is treated with bentonite, a natural, abundant and highly absorbent clay of volcanic origin. This cleaning process provides a regenerated oil that is suitable as a raw material for bio-lubricants as well as for the fabrication of other useful products. Wastewater from the process is managed, recovered and used in a new recycling cycle. Also, solid residues are collected to be assessed for reuse or valorisation.
From spin-off ideas to new applications
While WORLD initially focused on turning WCO into bio-lubricants, project work soon led to other promising applications. One was to use WCO as a material to capture volatile organic compounds (VOCs) from polluted air. These carbon-based chemicals are responsible for a plethora of adverse effects on human health and the environment(opens in new window); therefore, removing them from air or water is of paramount importance. Another application involved the chemical conversion of WCO to glycerol and a mixture of free fatty acids such as oleic acid through acid hydrolysis and further basification: both these plant-derived by-products were tested as components of so-called deep eutectic solvents (DESs), a class of compounds that are less toxic and also cheaper than traditional solvents. DES use in chemical processes is fully consistent with the green chemistry principle of using reactants and solvents from renewable rather than fossil sources. “Some of these ideas are already at practical proof-of-concept level, especially VOC capture; others are still at an earlier stage, but they show strong future potential,” Mannu and Mele say.
From public awareness to policy action
A significant part of the project work involved understanding the market, delivering training initiatives and encouraging public engagement. On a broader level, WORLD outcomes can support better EU-level decisions on WCO collection and treatment based on real technical evidence of its circularity potential. The results can also find application outside Europe, especially in areas producing large amounts of WCO. “The long-term vision is to make this technology replicable: suitable for different regions, different scales and different industrial contexts,” Mele concludes.
