Yeast is a single-celled organism that can consume sugars from this organic waste material. These starting materials are known as ‘feedstocks’, which the yeast then converts into alcohol and carbon dioxide, through fermentation. Common feedstock sources include corn, sugarcane, or cellulosic materials. Using non-conventional biomass sources, such as kitchen food scraps, as feedstocks could mean more of this clean energy can be produced and deployed.

The amount of food wasted, on an annual basis, amounts to 1.3 billion tonnes globally. The UN Environment Programme states that households account for 61% of this waste, with 6.4 million tonnes of household waste produced in the UK alone. Researchers at the University of Bath have been working to establish if we can ‘unlock’ energy from waste streams using some of this wasted food as a novel feedstock for biofuel production.

Bread to biofuel

Dr Sanjay Nagarajan, a researcher from the Department of Chemical Engineering is investigating recycling bread waste into bioethanol and biomethane. Through his research, Dr Nagarajan has designed a process for treating bread waste so it can more readily be used as a feedstock.

Dr Nagarajan’s study took inspiration from the idea of the circular economy. This is an approach where resources are kept in use for as long as possible to extract maximum value from them. One of the most commonly wasted food items in UK households is bread, with estimates that 20 million slices are wasted daily. Using bread as a feedstock fits neatly into this idea, adding new value to a previously wasted item.

When comparing his new process to conventionally used feedstocks like sugarcane and maize grain, Dr Nagarajan found that using bread produced a similar amount of bioethanol.

Engineering better biofuels

Yeast plays a vital role in converting feedstock to biofuels. Scientists have found that by genetically engineering its DNA, they can help the yeast work harder. Much like upgrading your computer’s software, adding or changing specific genes in the yeast cells makes them faster and more efficient at producing biofuels.

Under the supervision of Dr Daniel Henk and Dr Neil Brown in the Department of Life Sciences, biotechnology master’s students have been ‘tweaking’ the genetic makeup of a strain of yeast cells. Using a process called metabolic engineering, they’re hoping to make the yeast better at converting sugars into biofuels.

‘The yeast's metabolic pathways are the chemical reactions that occur inside the cell,’ explains George, a student in the laboratory. ‘By modifying these pathways, we can enhance the production of desired biofuels with novel feedstocks.’

The team is also experimenting with using waste onions as a novel feedstock. They hope future cohorts can continue to expand upon their research and apply this approach to other major food waste streams, such as those from the brewing or dairy industry.

The future of fuels

We are still a long way from seeing the effective utilisation of the vast streams of food waste in these energy-harnessing approaches, but this research marks a step in the right direction.

Current work demonstrates the promise of biotechnological approaches particularly, for sustainable and higher-efficiency biofuel production. Using cross-disciplinary approaches working to optimise the process of fermentation of food waste feedstocks, researchers at Bath are contributing to the development of the biofuels of tomorrow, whilst also tackling the issue of widespread food wastage in the UK today.

This article was written by Ellie Adams, a biotechnology master's student specialising in sustainable biotechnology in the Department of Life Sciences. It was produced as part of the Science Communication Ambassador project in the Faculty of Science.