Discarded oranges converted into electricity? Pulp but not fiction

Seville oranges / Photo source: Oxy design at Unsplash

Each year in January, the bleak UK winter grey skies and the harsh cold winds are alleviated for many by the appearance of recipes for Seville orange marmalade in cookery magazines and newspaper sections. It is a celebrated ritual: the oranges are at their best for a short period only from the end of December through to mid-February and deemed too bitter to be consumed as fruit like other varieties.

Much of the 17,000 tonnes of oranges produced in the region is exported to the UK. Although they provide an eye-catching colourful spectacle, many Sevillanos see them as a nuisance when they drop from around 50,000 trees around the city and are reduced to a pulpy mess which is hazardous to pedestrians and drivers alike. The burden placed on the 200 or so people employed to clear them from the streets of Seville is considerable.

Now, however, an innovative utilities company are turning unused oranges into electricity. Emasesa, Seville's municipal water company, is promoting a pilot project for the second year to generate clean energy from the juice of the oranges found on the streets. The oranges which languish on the streets go through a recovery process where they are added to an existing facility which generates electricity from organic matter.

About 50% juice and 50% peel are extracted from each orange. As the juice ferments, the methane emitted is captured to power a generator at the water purification plant. The discarded orange peels and pulp are, in turn, processed through a composting machine and used to fertilise fields in the province.

The pilot project undertaken in 2020 used 35 tonnes of bitter oranges which was sufficient to generate 1,500 kWh (kilowatts per hour) – equivalent to the consumption of 150 homes. While the pilot project focused on powering the water treatment plant, the long term aim is to add surplus electricity produced to the grid.

It has been calculated that if the 17,000 tonnes of bitter oranges produced in the region were put through Emasesa’s process, the electricity generated would be sufficient to power 73,000 homes.

Benigno Lopez, head of Emasesa’s environmental department, estimated that an investment of €250,000 by city authorities would allow all Seville’s oranges to be recycled by his company. Since the oranges would otherwise be consigned to a landfill site, the Emasesa project demonstrates the circular economy at its most efficient.

The even more encouraging news for Seville and Emasesa is that the quantity of oranges harvested during the 2020-2021 season is expected to show an increase of 37.5% over that of 2019-2020.