Little by little, awareness of the need to recycle used cooking oil is increasing, although we are still far from achieving the results of recycling plastic or paper. Vegetable oil is an organic compound that, once used, undergoes chemical alterations due to high temperatures and when it ends up in the sink or toilet, it causes problems in sanitation networks and contaminates river waters. In addition, recycled vegetable oil has several sustainable and beneficial uses that help reduce this environmental impact. “Some of the most common uses involve the possible production of biodiesel, soap manufacturing, generation of electrical or heat energy, or the production of bioplastics, etc…”, indicates Professor Carlos García Izquierdo, researcher at the Center for Soil Science and Biology. Applied Segura (Cebas) of the CSIC.
García Izquierdo recalls that not recycling used vegetable oil could produce a negative environmental impact, since “its uncontrolled discharge could cause problems for ecosystems as important as soil or water (one liter of used oil could contaminate up to 10,000 liters of water)” . Furthermore, waste recycling fully enters into a circular economy “increasingly necessary in our society, but this must be done without causing negative impacts on the environment,” he points out.
It is interesting to know about projects that are being carried out with used vegetable oil and that are having important results. Among them the Pretenacc project, Supported by the Ignicia program of the Galician Innovation Agency of the Xunta de Galicia, it aims to launch a pioneering method to manufacture bioplastics of plant origin. «It is the result of more than 10 years of work by a research team from the Cretus Center funded by various national and regional projects. The Pretenacc process aims to valorize used cooking oils for production through a biological process of biopolymers (polyhydroxyalkanoates or PHA) called bioplastics with properties similar to those of conventional plastics obtained from petroleum,” the researcher begins by explaining. by Cretus Anuska Mosquera. These bioplastics are therefore obtained from renewable sources, are based on a biological process and are biodegradable.
Future substitute
“In this way, the aim is to advance the management of used cooking oils, which are currently used to produce biodiesel, and convert them into a material, which is something that promotes the current EU waste recovery hierarchy,” he clarifies. The bioplastic obtained can be used “to progressively replace conventional plastics produced from petroleum, therefore reducing their negative effect on the environment,” he adds.
As Mosquera explains, the fundamental difference of this pioneering method lies in the biological process used, which “is made up of a reaction unit where all the biological processes necessary to obtain the bioplastic are carried out. These are the hydrolysis of the oil to make it accessible for transformation by the bacterial consortium, the growth of the microbial consortium with the capacity to accumulate bioplastics and the accumulation stage of these. To date, the processes that carry out the production of these bioplastics from waste streams are carried out in two or three separate reaction units that consist of a pretreatment of the waste, a development stage of the microbial culture and a final production stage. of bioplastic. “The fact of being able to produce the bioplastic in a single reactor reduces the construction and operation costs of the system,” emphasizes the researcher who works on the project together with her colleagues Alba Pedrouso Fuentes and María Ángeles Val del Río. On the other hand, it stands out that used cooking oil stands out as a very suitable waste since it has a little variable composition, which favors the bioplastic obtained to maintain its composition and, as a consequence, its plastic properties in very defined ranges.
At this moment, the scaling up of the biological process is being carried out at a demonstration level in a 600 L pilot plant installed in a used cooking oil management company, PMA Nutrigrás located in Mos (Galicia). “The results obtained are being used both for the optimization of the process and for the design of the process on an industrial scale that will allow us to know the costs of implementation and operation of a bioplastic production plant on an industrial scale,” explains the research team.
Green fuel
Last year Repsol launched a new plant at its Cartagena refinery with a production capacity of 250,000 tons of renewable diesel (HVO) and SAF per year that can be used in different vehicles with combustion engines. «This plant processes 300,000 tons of waste per year. Currently, we receive used cooking oil and agri-food waste,” explains Antonio Mestre, director of the Cartagena Industrial Complex. It is the first plant in the Iberian Peninsula in which these 100% renewable fuels are manufactured. To produce this fuel, 80% used oil and 20% other raw materials are currently being used. At the moment they are importing part of these materials, although the idea is to be able to carry out all production with used cooking oils and agri-food waste that come from Spain. This oil arrives at the port located in the Escombreras Valley and is unloaded in one of the four tanks that Repsol has with a capacity of 36,000 tons. It arrives at the plant after traveling 4.5 kilometers of heated pipes to keep it liquid and thus be able to transport it. Already in the heart of the plant, in the hydrotreatment unit, in a first phase the oil is treated with hydrogen and a catalyst, a substance that accelerates and facilitates a chemical reaction to break its molecular structure. However, it does not yet have the proper temperature properties and could solidify. It goes to the oven where it reaches more than 300ºC to be treated. And in the second phase, a new reaction occurs where the molecular structure of the product is transformed to guarantee its optimal functioning in cold situations. Finally, in the fractionation tower it is subjected to different pressure and temperature conditions to obtain renewable fuels for aviation and renewable diesel that is used in different transportation sectors.
Last year, Repsol launched a pioneering plant at its Cartagena refinery in which cooking oil and other agri-food waste is transformed into renewable fuels.
Scalability is the great pending challenge of some of the most innovative projects
Carlos García Izquierdo, researcher at CEBAS of the CSIC, explains that the production of biodiesel from used vegetable oil in turn generates some waste such as crude glycerin as the main product, wastewater, as well as some type of residual sludge. «The aforementioned waste generated has the potential to be used through adequate anaerobic digestion. The anaerobic digestion of organic waste will occur, in the case of those derived from obtaining biodiesel, as long as there is a pretreatment to avoid some contaminants and thus eliminate problems in the system. In addition, these wastes can also be mixed with other types of organic substrates, in order to improve the production of biogas in the proposed anaerobic digestion process,” he indicates.
A few years ago, the CEBAS-CSIC research group participated in the European project Valuvoil, investigating the possibility of using the digestates that appear after the anaerobic digestion of waste derived from the previous obtaining of biodiesel, as a possible fertilizer in agriculture. “In general, we know that all anaerobic digestion processes of organic waste lead to the appearance of a new waste called digestate or digestate,” emphasizes García Izquierdo. His research group carried out research aimed at understanding the effects that digestates have when they are valued in agriculture, as a possible organic fertilizer. Experiments were developed using digestates obtained both at the laboratory level and with those resulting from the prototype used in the project, to demonstrate whether they are suitable for use in agriculture. «All the tests carried out led to the conclusion that this type of digestate can be used in agriculture, as long as there is control over it, keeping in mind the following aspects: the characteristics of the digestate since these must be suitable for its valorization in agriculture, because they should not contain any type of undesirable contaminant; propose adequate management of digestates, either “raw”, or separated into their two fractions, liquid and semi-solid, with the necessary dose adjustments; There is a need to monitor, both in soil and in plants, the effects derived from the use of this fertilization source, in comparison with other conventional ones,” he points out.
Above, image of the bioplastic obtained from the Pretenacc process from used oils. Below, image of the Pretenacc project research team. From left to right: Alba Pedrouso Fuentes, Anuska Mosquera Corral and Ángeles Val del Río, members of the Cretus center of the University of Santiago de Compostela
Valuvoil has shown that these digestates can provide essential nutrients for crops and improve soil quality, provided they are properly managed. There are other success stories in which the digestates generated during the anaerobic digestion of waste have been used effectively in agriculture as fertilizers.
They are projects that confirm that innovation has recipes for success to turn the problem of this waste into profitable solutions.
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