Research developments

Scientists turn tomato waste into electricity

A team of scientists is exploring an unusual source of electricity — damaged tomatoes that are unsuitable for sale at the grocery store. Their pilot project involves a biological-based fuel cell that uses tomato waste left over from harvests in Florida.

The researchers presented their work March 16 at the 251st National Meeting & Exposition of the American Chemical Society (ACS) in San Diego, which featured more than 12,500 presentations on a wide range of science topics.

“We have found that spoiled and damaged tomatoes left over from harvest can be a particularly powerful source of energy when used in a biological or microbial electrochemical cell,” says Namita Shrestha, who is working on the project. “The process also helps purify the tomato-contaminated solid waste and associated waste water.”

Shrestha is a graduate student in the lab of Venkataramana Gadhamshetty, Ph.D., P.E., at the South Dakota School of Mines & Technology. They are collaborating on this project with Alex Fogg, an undergraduate chemistry major at Princeton University. Other project collaborators include Daniel Franco, Joseph Wilder and Simeon Komisar, Ph.D., at Florida Gulf Coast University.

Tomatoes are a key crop in Florida, notes Gadhamshetty. He stresses that the project is important to the state because Florida generates 396,000 tons of tomato waste every year, but lacks a good treatment process.

Gadhamshetty began working on the topic as 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.”

So, the team developed a microbial electrochemical cell that can exploit tomato waste to generate electric current. Shrestha explains, “Microbial electrochemical cells use bacteria to break down and oxidize organic material in defective tomatoes.”

The oxidation process, triggered by the bacteria interacting with tomato waste, releases electrons that are captured in the fuel cell and become a source of electricity. The natural lycopene pigment in tomatoes, the researchers have found, is an excellent mediator to encourage the generation of electrical charges from the damaged fruits.

Some of their results proved to be counterintuitive.

“Typical biotechnological applications require, or at least perform better, when using pure chemicals, compared to wastes,” Gadhamshetty notes. “However, we found that electrical performance using defective tomatoes was equal or better than using pure substrates. These wastes can be a rich source of indigenous redox mediators and carbon, as well as electrons.”

At the moment, the power output from their device is quite small: 10 milligrams of tomato waste can result in 0.3 watts of electricity. But the researchers note that with an expected scale up and more research, electrical output could be increased by several orders of magnitude.

According to calculations by Shrestha, theoretically enough tomato waste is generated in Florida each year to meet Disney World’s electricity demand for 90 days using an optimized biological fuel cell.

BioHiTech America to test new process for handling effluent

BioHiTech Global Inc., a green technology company that provides a solution for food waste disposal, announced that its subsidiary, BioHiTech America, based in Chestnut Ridge, New York, has partnered with Natural Systems Utilities, Ridgewood Green RME and the Village of Ridgewood, New Jersey, to test a process that will allow BioHiTech’s Eco-Safe digester to digest, tank and deliver the effluent from its Eco-Safe digesters to anaerobic digestion (AD) facilities anywhere in the world.

BioHiTech’s Eco-Safe digester utilizes an aerobic digestion process to convert food waste to grey water, also referred to as effluent with a new process that will tank the unit’s effluent, allowing for transportation to an anaerobic digestion plant where biogas can be captured and used to create renewable energy.

The Eco-Safe Digester performs the hydrolysis stage of AD at the point of origin. Because the aerobic digestion process begins with the breakdown of solid organics to a liquid slurry, the effluent is able to be easily pumped and transported, arriving at the AD facility in a “predigested” condition allowing for efficient feedstock transfer and eliminating the need for costly processing at the AD facility, says the company.

This new process is currently being tested at a high-volume supermarket in New Jersey and transported to a Ridgewood, New Jersey water pollution control facility.