The city of Seville is one of Spain’s historic hubs, primarily known for being the birthplace of flamenco, and a passionate preserver of bullfighting. But it’s also a citrus haven: With almost 50,000 orange trees, it’s Europe’s top city for orange production.
But these are not oranges to be consumed fresh. An Andalusian travel guide bluntly warns, “The oranges can’t really be eaten fresh, unless you are a food masochist or eat lemons with their peel, like an apple.” Rather, Seville oranges are prized for their tart cooking properties—especially among the British for their use in marmalade, so most are exported to the U.K. with every harvest. But a huge number of those bitter oranges, introduced by the Moors in the 10th century and a Seville staple ever since, simply fall from the trees and end up on the streets. The city employs 200 people to collect oranges from the roads, for use as fertilizer or to be sent to landfills.
Now, for the first time, the recovered oranges are being used for another purpose entirely: to generate electricity.
This year, the city’s council and its parks department have rolled out a pilot program with EMASESA, Seville’s water supply and sanitation division, whereby electricity from oranges will power the department’s largest water purification plant. Specifically, it’s the methane released by the oranges as they ferment that drives the generator. The oranges are collected from the streets in vats and then machine-ground to extract the juice, for producing the biogas. The rest of the fruit, including the peel, will be used as fertilizer or compost.
“It seems that the bacteria that we use to produce methane really like the juice from our oranges, which works very well,” said Enrique Vaquerizo, chief of the wastewater department at EMASESA, to a group of journalists on a tour of the site.
The pilot will use 35 metric tons (about 38.6 U.S. tons) of oranges, which is likely to produce 1,500 kWh of energy, enough to power about 150 homes. EMASESA’s four plants are already 70% powered by renewable sources—principally methane from sewage sludge—but its goal is to reach 100%.
Europe is the global leader in biogas, which can use the waste of many different types of food, including animal proteins, grains, and vegetables, to produce electricity. In 2015, the continent accounted for half the world’s biogas creation, including 18 billion square meters of methane, and biogas is a significant source of energy in countries including Germany, the Czech Republic, and Latvia. Biogas is a growing trend in the U.S., with Brooklyn, Los Angeles, and Salt Lake City among the municipalities boasting production facilities.
The ultimate goal in Seville is to get surplus electricity back into the grid, for which oranges could prove to be pivotal. The forecast for the orange harvest this year is 5.7 million kilograms, a 38% increase over last year, and the city typically recovers about 17,000 metric tons a year just on the roads. (It’s also been noted that the customs changes brought about by Brexit may force Britain to reduce its reliance on European fruit, perhaps creating even more leftovers.) Based on trial estimates, the city assesses that if it used all of those recovered oranges, it could power 73,000 homes for a year.