New doctoral research by Getachew Birhanu Abera shows that biofilm-based systems can make biological conversion of carbon dioxide to methane more efficient and resilient. The work offers new insights into how renewable gas production can withstand impurities commonly found in biogas.
As global demand for clean energy surges due to rapid economic growth and recent geopolitical shifts, biomethane has emerged as a promising alternative to fossil fuels. It can be produced from organic waste and injected into existing gas grids, making it a practical option for a low-carbon future. The European Union targets a sevenfold increase in biomethane production from 2023 to 2030.
While biomethane is a sustainable alternative to fossil fuels, traditional biogas purification methods are energy and cost intensive (often rely on toxic and costly chemicals). In contrast, biological biogas upgrading, so-called biomethanation offers a greener path, yet its efficiency is frequently hindered by impurities generated during biodegradation of organic wastes, such as hydrogen sulphide and ammonia.
“The aim of my PhD project was to overcome key bottlenecks in biomethanation by using attached microbial communities, or biofilms, instead of conventional suspended systems,” PhD candidate Getachew Birhanu Abera explains.
A suspended system is a bioreactor where microorganisms float freely in the liquid rather than growing attached to a surface or forming biofilms. Biomethane is mainly made of methane, the same energy-rich gas found in natural gas.
One way to increase biomethane production is biomethanation, a biological process where microorganisms convert carbon dioxide into methane using hydrogen as a reducing agent. This approach is attractive because it is energy and cost effective, avoids the use of harsh chemicals, and uses natural microbial activity instead.
Combining laboratory experiments and computer modelling
Abera combined laboratory experiments and computer modelling. He tested different types of bioreactors exposed to controlled amounts of hydrogen sulphide and ammonia and compared systems with and without biofilms. Gas production, methane content, and microbial communities were analyzed. To better understand what was happening inside the reactors, he also used a mathematical model to simulate the biological processes. This helped explain why biofilm systems were more stable and predicted how they would behave under different stress conditions.
Biofilm-based bioreactors are resilient
Abera’s results confirmed that while hydrogen sulphide and ammonia negatively impact biomethanation and alter microbial community structures, biofilm-based bioreactors are very resilient.
“These systems maintain superior performance compared to the suspended systems,” he says.
This is because the biofilm formed on the biocarrier material added acts as a protective shield for the microbes, allowing them to continue converting carbon dioxide into methane.
This doctoral work demonstrates how biofilm-based systems can mitigate the negative impact of hydrogen sulphide and ammonia on biomethanation. Abera’s findings serve as a foundation for future research on biomethanation.
“In the future, this could mean industrial-level applications of biofilm-based bioreactors in waste treatment and energy recovery under inhibitory conditions,” he says.
“By making the process more resilient, we can turn difficult waste streams into a reliable source of renewable energy.”
Getachew Birhanu Abera will defend his PhD thesis “Biological conversion of CO2 to CH4: impact of process inhibitors and biofilm-based mitigations approaches” Thursday 16 April, 2026.
Trial lecture and public defense are open all - read more about that here.