Around one-third of the food produced around the world today is wasted. That includes everything from produce that rots in trucks during transit to meat that doesn’t sell in stores to leftovers at home and in restaurants. This wasted food is an untapped energy resource.
Engineers at Cornell University have now come up with a fast, effective way to convert foodstuff into fuel. Their two-step process, detailed in the journal Bioresource Technology, extracts nearly all the energy present in trashed food.
Wasted food squanders land, water, and energy, while producing unneeded greenhouse gas emissions. But food scraps are rich in carbon. If even a portion of wasted food is diverted to make energy, it could produce a lot of fuel to heat homes and power vehicles while saving landfill space.
There are now hundreds of industrial-scale waste-to-energy systems in countries around the world. They typically use anaerobic digesters, in which microbes break down organic matter and convert it into fuels such as methane, biodiesel, or ethanol. But the process takes weeks.
The Cornell team added a process called hydrothermal liquefaction before anaerobic digestion. The liquefaction step involves pressure-cooking food waste at temperatures of 200–350°C and pressures of 2–20 megapascal.
In their laboratory test, the researchers used a mixture of sugars, proteins, and fats as a proxy for food refuse. They got two products as a result. One was a bio-crude oil, which can be refined to make a liquid biofuel. The other was wastewater containing dissolved organic carbon. Microbes can digest this aqueous waste and convert it into biomethane within days.
The researchers found that higher temperatures resulted in more bio-crude oil and an aqueous phase that was harder for microbes to biodegrade.
Combining hydrothermal processing and anaerobic digestion recovers more energy from discarded foodstuff by converting it into two products: oil and biomethane. It is also more efficient and faster than anaerobic digestion alone, Roy Posmanik, the lead author of the study, said in a press release. “We’re talking about minutes in hydrothermal liquefaction and a few days in an anaerobic digester.”