Long has it been since the topic of waste and consumption was merely used by a select few. Today, these issues come up regularly from small businesses, large corporations, and even governments around the globe. Moreover, the dawn of sustainability has yielded an awakened understanding of how impactful rubbish can be.
This spotlight has exposed individuals to just how much junk they create annually, whether directly or indirectly. Likewise, the shift in sustainable mindfulness has led many to examine what they throw out and how they could repurpose it for better use.
Bioenergy in Seville
Take a walk down the bustling and historic streets of Seville, Spain, and you might notice one of the 50,000 orange trees that call this town home. The trees are a familiar sight for the city and draw in a substantial number of tourists during the springtime when the orange blossoms fill the air with their sweet aroma. On the contrary, not everyone is a fan of the fruit as it often inconveniences the locals.
Though some oranges are packaged and shipped north to Great Britain, the abundance of trees makes it impossible to harvest each one. This means that the remaining fruit typically falls into the streets or on buildings and is wasted.
Seville's Water Utility company has devised a plan to prevent this waste by harvesting the leftover fruit to generate electricity. The utility company's environmental program head, Benigno Lopez, explains the method: "Look, it's a very simple process: 50% of that orange is juice. Through this juice, we generate a gas rich in methane that we use to produce energy." To start, the company plans to use the energy to help run their purification plants, effectively lowering their environmental footprint and ridding the streets of Seville of fallen fruit.
Eventually, they want to expand their reach to power homes in the surrounding area. They estimate that roughly 2300lbs of oranges could produce 50 kWh of electricity. When considering the number of oranges in the city, the company figures that it could generate enough energy to power up to 73,000 homes, more than 10% of Seville's population.
The water utility company will then take the remaining pulp of the orange and utilize it as a fertilizer for agricultural purposes.
Lopez says that the process "does not require any type of additives, it is environmentally controlled and it closes the circular economy of urban waste, which also means that this facility contributes to mitigating climate change by self-sufficient energy."
Harvesting Energy from Waste
The type of energy the city's water utility company aims to produce is biomass: renewable energy produced from organic matter, such as agricultural waste, forest waste, food waste, and microalgae.
The aforementioned organic matter contains stored chemical energy from the sun obtained through photosynthesis. This energy is then extracted and converted to electricity.
There are four main ways to harvest energy from biomass, direct combustion, thermochemical conversion, chemical conversion, and biological conversion. Even though the utility company doesn't explicitly say how they will be transforming the orange juice, we can assume it is via direct combustion due to its ease and popularity.
Direct combustion "is a thermochemical technique in which the biomass is burned in open air or in the presence of excess air. In this process, the photosynthetically stored chemical energy of the biomass will be converted into gases. Generally, direct combustion is carried out inside a furnace, steam turbine, or boiler at a temperature range of 800–1000°C."
Despite biomass being a promising renewable energy source, some discrepancies occur if the method is done incorrectly. This can typically be seen in instances when water or energy-intensive crops are grown simply to be used for biofuel, such as with corn. Due to the number of resources needed to produce certain crops and the harvesting process, the entire manner can emit more emissions than what is saved, resulting in what is known as a carbon debt.
The best way to avoid carbon debt is to use agricultural waste or algae. The way Seville's Utility company is approaching the process, by using orange waste that isn't explicitly being grown solely for generating fuel, means that they can avoid the excess emissions and produce a low-to-zero-emission energy source.
Since the pilot is still in its early stages, it can be assumed that the process will be streamlined as the test studies continue. With a high possibility of success, the company will soon be able to convert large quantities of orange juice into usable energy effectively. With the potential to supply nearly 75,000 homes with clean fuel, the company could dramatically help to reduce the city's environmental footprint. Likewise, they could encourage other companies in surrounding cities or countries to utilize similar techniques to yield a future of cleaner energy and less waste.