Background Spain is Europe’s largest producer of citrus fruit with an output of 6 million tonnes a year. Some 1.6 million tonnes of this total goes to produce fruit juice, giving rise to 800 000 to 900 000 tonnes of peel and pulp waste per year. This waste is highly problematic waste for the environment. The only existing alternative to landfilling of citrus fruit waste is its use in fresh animal feed. However, the high water content of the fruit wastes – 78-82% – results in high transport costs and leakage of contaminating liquids. D-Limonene is the main component of the essential oil of the peel. This component can ferment and contaminate aquifers. Desiccation is often a means of treating citrus waste. The fruit leftovers are pressed and completely dried in adiabatic tunnels with warm air. However, the high biological oxygen demand (BOD) of the wastewater is difficult to treat, and the process is energy intensive. Additionally, this process is only carried out with a view to reducing transport costs rather than the beneficial use of the waste. Objectives The CITROFUEL project’s main objective was to develop a new process to improve the management and sustainable use of natural resources and waste from citrus fruit production. The project planned to construct and run an industrial prototype for producing bio-ethanol from the biomass waste generated in the production of animal food from citrus waste by means of a new fermentation process. In improving prevention, recovery and recycling of citrus fruit waste, the beneficiary aimed to turn management of citrus fruit waste into an opportunity to bolster the second generation biofuel sector. The beneficiary would publish a document detailing the current status of bio-alcohol production from a technical and a legal/administrative point of view. A second publication would set out the findings and conclusions of the project implementation. Results The CITROFUEL project constructed and demonstrated an industrial prototype for producing bio-ethanol from the fluids generated in animal food production from citrus waste. The prototype uses a new fermentation process. To this end, the project built on the research carried out by the Technical University of Valencia (UPV) on bio-ethanol production from fluids generated by the processing of citrus waste. At lab scale, the UPV research showed that a viable conversion rate of the fermented waste to the alcohol end product could be achieved – 0.08 litres of 92º alcohol per litre of fermented liquor. However, these projections were not met at industrial scale. The production rates generated by the prototype industrial plant were lower than hoped; the conversion rate was 0.04 litres of 92º pure alcohol from one litre of fermented liquor. The average production costs of ethanol from the fermentation and distillation of liquors from orange residue are currently high, reaching double than those generated in the production of bioethanol from cereal crops. The installation of a cogeneration plant can reduce energy costs by around a third in the production of bioethanol from orange pulp.An improved production rate of 0.08 could be achieved, however, by increasing the amount of fermentable dry material. But doing so reduces the amount of animal food produced and lowers its economic viability. Furthermore, the price of the bioethanol end product was considerably lower (€0.3 /litre) than that estimated by the UPV (€0.8 /litre). In total, the project processed 2 250 tonnes of citrus waste (775 t in 2011 and 1.475 t in 2012), producing some 38 000 litres of bioethanol (12 920 and 25 097 litres for 2011 and 2012 respectively). Therefore, an average of around 60 tonnes of waste was required to produce one litre of bioethanol. From an environmental perspective, the process developed resulted in an average emission saving of 45.9 tonnes of CO2 per litre of bioacohol produced. The trials also affirmed the need to maintain operation of the bioethanol plant every day of the week, and thus the need for a minimum continuous supply of citrus waste. Such a continuous supply, however, is difficult to guarantee. The project also highlighted the importance of the orange pulp pressing process. The higher the efficiency of the pressing, the greater the amount of liquid obtained, and hence the more product to be fermented and distilled. Furthermore, inadequate disposal of essential oils can inhibit fermentation and render the process less efficient. In conclusion, the project proved an environmentally friendly solution for producing bioethanol out of citrus waste. Unfortunately, this solution is not yet economically feasible. Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).