Waste Not
This Spanish Water Utility Is Turning Orange Waste Into Green Power

In the Andalusian city of Seville, the spring air is sweet with the scents of orange blossom and limonene. But come winter, it’s not so sweet — there is no escaping the 5.7 million kilos of fruit littering the streets. Deposited from 48,000 orange trees, the oranges — too bitter to eat — cause huge disruption and inconvenience to the people of Seville. Some oranges are shipped to England to be made into Grand Marnier, Cointreau and marmalade — and the peels used in bitters; however, with such vast quantities, the city has struggled to find a solution of how to deal with the millions of kilos left over.

“When fruit falls, it should not be ‘waste’; with the right planning and subsequent management, the oranges should be used for good with minimal environmental impact, adding value to the city of Seville,” Benigno López, Head of the City’s Environment Division, told Sustainable Brands™.

And that is exactly what Emasesa, a municipal water company based in Seville, has done. Through the technology available at its wastewater treatment plant (WWTP), the company has launched a pilot scheme collecting this unwanted fruit and transforming it into energy through a process known as co-digestion or joint-anaerobic.

“The juice extracted from pressing the oranges is introduced into the digester at the wastewater treatment plant,” López explained. “It then undergoes a biological process in which organic matter is broken down due to the existing bacteria in the environment. The process is essentially carried out due to the absence of oxygen.”

Limonene, a component of orange peel, is an antimicrobial agent that impedes biogas production when digesting peels. However, if the oranges are pretreated and the limonene removed before the digestion process, then the methane yield emitted from the oranges increases through the process known as anaerobic fermentation. This methane generated through the gaseous fuel from the biomass can then be used as fuel for electricity.

Emasesa harvests the oranges manually with the help of around 200 workers. “This is the most economical way to do it, as the distribution of orange trees throughout the city is uneven. They are scattered through avenues, squares and streets for example, with an unequal production per unit ranging from 45 and 130 kilos per tree,” López said. “The oranges collected are then converted into energy — every 1,000 kilos of oranges generates 50kW of energy, which is about the consumption of 5 homes a day.”

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Emasesa boasts that the WWTP is a benchmark for a circular economy, and the company anticipates that the Copero WWTP will eventually become an environmental innovation centre in itself.

“We are hoping that this site will allow for innovative solutions surrounding water and waste treatment, as well as generating a self-sufficient energy supply,” says Alberto Ortiz, Head of the Department of Environmental Management and Climate Change at Emasesa.

Furthermore, Emasesa is also planning on creating quality compost by recovering the WWTP sludge (semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater) and biomass (pruning remains) from the parks and gardens of Seville.

“We are hoping to promote the co-digestion of waste with a high organic load. Then, in order to produce more biogas, we are planning to investigate whether the waste from the pre-water treatment (sand and floating) could be used to digest urban solid waste generated in the city,” López explained.

When asking Emasesa about the environmental implications of using biofuels, they say that the majority of aspects are positive. However, Ortiz acknowledged that “energy performance can be quite low. And waste can be accumulated — for example, we have to utilize 45-50 percent of the resulting weight after pressing the pulp; in our case, by compositing.”

He further went on to explain the complications of biofuel: “The biggest problem is actually getting to it — the biogas generated must be purified and transformed before it can be used as biofuel. This process requires investments in equipment and technology, and so therefore can be very expensive.”

Despite this, and with the advantages outweighing the disadvantages, Emasesa continues forward on its quest for sustainability. Spain is heavily invested in environmentalism and renewable energies; and in 2018, the government launched an ambitious scheme to have 100 percent renewable energy by 2050 — initiatives such as Emasesa’s will only help fuel the scheme's success.