Waste bread could replace fossil fuels with carbon-negative chemistry

Most of us see a heel of dry, forgotten bread as a candidate for the bin, or perhaps a snack for the birds. 

Scientists at the University of Edinburgh, however, see it as the potential solution for the chemical industry.

They used waste bread to power hydrogenation — a vital chemical process that currently produces everything from pharmaceuticals to plastics.

Particularly, a common strain of E. coli was used to consume sugars from waste bread. This new technique offers a scalable, green alternative for various industries.

“Hydrogenation underpins huge parts of modern manufacturing, but it still relies almost entirely on hydrogen made from fossil fuels,” said Professor Stephen Wallace, Personal Chair of Chemical Biotechnology, School of Biological Sciences, University of Edinburgh. 

Fossil-free process

Modern manufacturing processes depend mostly on carbon-emitting fossil fuels. 

Specifically, the hydrogenation process has relied on hydrogen gas derived from fossil fuels. 

Hydrogenation is an industrial process used to transform substances like liquid vegetable oils into stable solid fats and to synthesize pharmaceuticals, plastics, and fuels. 

This reaction typically relies on metal catalysts — such as nickel, palladium, or platinum — to drive chemical production across a wide range of essential goods.

However, it is a carbon-heavy, energy-intensive cycle that demands extreme pressure and temperatures rivaling those at the bottom of the ocean.

Professor Wallace’s team has slashed the need for fossil-fuel hydrogen in chemical manufacturing by developing a clever, single-flask method powered by waste bread.

The study reveals that hydrogenation can be powered by hydrogen gas generated naturally by living bacteria.

In the process, a common strain of E. coli was fed with sugars extracted from discarded bread to create a biological engine.

In an oxygen-free environment, these bacteria produce their own hydrogen gas. When combined with a tiny amount of a metal palladium catalyst in a sealed flask at near-room temperature, the reaction occurs without a single drop of fossil-derived fuel.

This microbially produced hydrogen successfully fueled the hydrogenation of target chemicals under mild, low-energy conditions.

Greener horizon

The implications of this one-pot microbial method are many.

This process turns a waste management burden into a manufacturing asset by diverting bread from methane-emitting landfills and replacing it with hydrogen derived from fossil fuels.

“What we’ve shown is that living cells can supply that hydrogen directly, using waste as a feedstock, and do so in a way that can actually be carbon-negative,” Wallace explained. 

“This approach isn’t limited to food chemistry either. Hydrogenation is used across pharmaceuticals, fine chemicals, and materials. Being able to run these reactions using microbial hydrogen opens up new possibilities for sustainable manufacturing at scale,” the author added.

The team now looks toward their next phase of research, which aims to eliminate the need for metal catalysts entirely. 

Experts believe this carbon-negative, bio-based method could ignite a green industrial revolution in the UK and beyond. The technology offers a sustainable blueprint that researchers hope will inspire further corporate partnership and innovation for manufacturing using renewable and waste-derived materials.

The study was published in Nature Chemistry on February 23.