Energy from supermarket waste

 By Benjamin Plackett

A team of scientists is exploring the potential of damaged tomatoes — no longer suitable for sale at the grocery store — as an energy source. Their project employs a microbial-based fuel cell that uses tomato waste left over from harvests in Florida. When bacteria interacts with tomatoes, a process of oxidation begins, where electrons are released and then captured to be stored as a source of electricity. The researchers have concluded that rotten and damaged tomatoes left over from the harvest are actually a powerful source of energy. To give some scale, Florida alone produces nearly 400,000 tonnes of spoiled tomatoes every year. The researchers say 10 milligrams of tomato waste equates to 0.3 watts of electricity, which they say will be improved when the process is conducted at scale…

Every day supermarkets throw out fresh fruit and vegetables — either because they’re not perfect enough to earn a place on the shelf or because they pass their sell by date — but now a group of scientists have looked at using this waste to generate electricity instead of landfill.

They used microbes to extract the energy inside damaged tomatoes, which was then captured and stored within a system made up of a series of electrodes and inter-connected circuits.

“The bacteria oxidize all of the carbohydrates in the tomatoes and frees up electrons, which is essentially the production of electricity,” explains Namita Shrestha, a graduate student at South Dakota School of Mines & Technology who worked on the research project alongside other scientists. “The electrons flow out towards the electrodes in the bio-electrical device,” she adds.

The results from this experiment were presented at the American Chemical Society’s national meeting in California last month. Shrestha and her colleagues sought to measure exactly how much energy can be squeezed from waste tomatoes. “We have calculated that 10 milligrams gives 0.3 watts per hour,” she says.

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That may sound like a small figure, but when the scale of the food waste problem is fully considered, it could hold the potential to produce a considerable amount of energy.

In Florida alone, where the tomato crop is key, waste reaches almost 400,000 tons a year, making the potential input for Shrestha’s system significant. “We could run Disneyland for 90 days just from Florida’s tomato waste based on our lab experiments,” says Shrestha. This microbial extraction of electricity could be used with almost any kind of fruit or vegetable, not just tomatoes.

However, the main barrier for this technology is to find a way to scale it up from small lab-based experiments that deal with milligrams into an industry-wide effort that deals with tons. “It’s a big challenge,” confesses Shrestha, “you need bigger machines and it can get expensive. It would require new infrastructure and so investment.”

It may be some time before theme parks of the future are powered by leftover fruit and vegetables. But Shrestha and her fellow researchers have already been approached by companies and environmental groups who want to help with these practical challenges. “It’s something we’re working on right now,” she says.

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about the author
Benjamin Plackett
I’m a journalist based in London. I report on all things science, tech, and health for a number of different publications. My work has been published by The Daily Dot, Inside Science and CNN among others. I earned my M.A. in Journalism at New York University and my B.Sci in Biology from Imperial College, London.