Every year, industries and households release huge amounts of carbon dioxide (CO2), a greenhouse gas that accelerates global warming and drives climate change. Instead of treating CO2 as waste, researchers have been exploring ways to use it as a feedstock for chemical production, a process which currently relies heavily on fossil fuels. One promising approach is to use microorganisms that consume CO2 for growth and bioproduction. Like all living organisms, these microbes require an energy source. While humans rely on food as energy source, certain microorganisms can harness electricity to power CO2 conversion through a process known as microbial electrosynthesis (MES).
Traditionally, MES research has focused on producing acetate, the main component of vinegar. Acetate is far from trivial: serving as a platform chemical with wide-ranging applications, including solvents (such as ethyl acetate in paints, coatings, and adhesives), food additives, pharmaceuticals, catalysts, and even specialty materials. However, despite its versatility, acetate has a relatively low market value compared to other bio-based chemicals.
In contrast, butyrate holds more potential. It is a short-chain fatty acid with higher commercial value and diverse applications in nutrition, gut health, biofuels, plastics, and specialty chemicals. To shift production from acetate to butyrate, Hui Yao and his collaborators introduced methanol as a co-feedstock alongside CO2 in the MES process.
“The addition of methanol enhanced both the productivity and selectivity of butyrate formation, which were further improved by optimizing the process conditions. We also investigated the composition of the unique microbial consortium involved and uncovered the metabolic pathways that channel methanol and CO2 into butyrate,” he says.
His research addresses a critical global challenge: reducing greenhouse gas emissions while developing sustainable methods for producing bio-based chemicals. By directing renewable electricity from wind or solar into living microbes, we can transform CO2 and methanol into butyrate in a controlled and efficient process.
“Rather than simply capturing carbon emissions, we can now envision transforming them into valuable biochemicals,” says Hui Yao.
Public defence on Friday 24 October
The doctoral dissertation of MSc (Tech) Hui Yao in the field of Environmental Engineering titled Butyrate Production from Methanol and CO2 in Microbial Electrosynthesis will be publicly examined at the Faculty of Engineering and Natural Sciences at Tampere University at 13 o’clock on Friday 24 October 2025 at Hervanta campus, in Festia building, auditorium Pieni Sali 1 (Korkeakoulunkatu 8, Tampere).
The Opponent will be Professor Eileen Yu from University of Southampton, the United Kingdom. The Custos will be Professor Marika Kokko from the Faculty of Engineering and Natural Sciences, Tampere University.