Turning Damaged Tomatoes Into Electricity Using Microbial Fuel Cells

Packing up harvested tomatoes in Florida
Tomatoes that don't make it to the grocery store due to damage create nearly 400,000 tons of waste in Florida alone each year. Scientists have found that the waste can be converted to energy within microbial fuel cells. Reuters

Outside of California, Florida is the second most prolific grower of tomatoes in the U.S., according to the U.S. Department of Agriculture. Together the states produce two-thirds to three-fourths of all commercially grown tomatoes in the country. Only China brings more tomatoes to the world's table. With all that output comes waste: In fact, it turns out that if you could convert all the tomato waste made in Florida over a year to energy, it could generate enough electricity to power Disney World for 90 days.

Under the direction of Venkataramana Gadhamshetty, professor at the South Dakota School of Mines & Technology, a team of researchers have found that damaged tomatoes left over from harvest can be a powerful source of energy when used in a microbial electrochemical cell. So far, the team has been able to turn 10 milligrams of tomato waste into 0.3 watts of electricity, a modest start they hope to improve upon with additional research. Initial study results showing tomatoes are viable energy sources within microbial fuel cells were published in Journal of Power Sources in 2014. At the 251st American Chemical Society this week in San Diego, the scientists will report on their ongoing efforts to identify ways to optimize the fuel cell to increase electrical output.

Tomatoes that don't end up in the produce section or inside a ketchup bottle add up to massive amounts of environmental waste. In Florida, nearly 400,000 tons—or as much as 40 percent of tomatoes produced—are tossed out each year, according to Alex Fogg, an undergraduate chemistry student at Princeton. During his summers spent at home in Naples, Fogg began working with Gadhamshetty, then a professor at Florida Gulf Coast University. "The project began a few years ago when Alex visited my lab in Fort Myers, Florida, and said he was interested in researching a local problem, especially local tomatoes grown in our state and the large waste treatment issue," Gadhamshetty says. "We wanted to find a way to treat this waste that, when dumped in landfills, can produce methane—a powerful greenhouse gas—and when dumped in water bodies, can create major water treatment problems."

A microbial, or biological, fuel cell harnesses the current produced by the breakdown of organic material by bacteria. According to Fogg, a number of other studies have shown other types of food waste, as well as marine waste, to be viable for use in fuel cells. This is the first to look into the potential of using tomato waste as fuel. Gadhamshetty, Fogg and team would put a tomato inside of a specially developed microbial fuel cell. Bacteria sourced from a local wastewater treatment facility is then introduced to the cell, where it oxidizes the tomato waste and triggers the release of electrons that are captured by the fuel cell and channeled into electrical currents. The process also helps purify the tomato-contaminated solid waste and associated wastewater.

The researchers believe that thiamin and riboflavin in tomatoes help transport charge between the fruit and the fuel cell. Their plans now are to fine-tune the process to increase electrical output—whether or not this technology is viable in the real world depends on the researchers' ability to figure out how to scale it up. A larger surface area of bacteria would obviously increase output, according to Fogg, but the specifics of how to scale up the project are a subject of ongoing research.

At this week's conference, the scientists explained testing methods that isolate parts of the process that produce the greatest resistance to the electrical charge transfer. They plan to improve the cell by determining which of its parts—electrode, electricity-producing bacteria, biological film, wiring—are resisting the flow of electricity. Then they will tweak or replace that part.

Fogg hopes the technology can eventually be used in a variety of applications, including in rural areas of the developing world that lack reliable access to waste treatment and the power grid. He expects that outside of those areas tomatoes would be sourced from processing plants and packing houses since about 80 percent of tomatoes undergo processing. However, tomato waste could also be sourced on-site at farms in communities where that type of processing doesn't occur—and where needs for innovative sources of power are quite high.