Tunnel drainage systems are important components of large underground structures, such as railway tunnels. These systems collect and redirect excess rain and groundwater, preventing flooding within the tunnel. Over time, however, the drainage pipes and collection points in these systems can become clogged or corroded by microbial biofilms, leading to maintenance challenges.

In a recent study, microbiologist Günther Koraimann at the University of Graz, in a collaboration with researchers from the Technical University of Graz, investigated the microbial life within tunnel drainage systems. Specifically, the researchers studied the Koralm Tunnel – a railway tunnel currently under construction in Austria. They wished to identify the bacteria responsible for biofilm formation, and to understand their impact on tunnel infrastructure.

Professor Koraimann, together with his research technician Karin Bischof, collected and analysed biofilm samples from various sections of the tunnel. Their analysis revealed that the biofilms in the Koralm Tunnel are predominantly made up of methanotrophic and autotrophic bacteria. Methanotrophic bacteria consume methane as their energy source and play a major role in underground carbon cycling. Autotrophic bacteria, on the other hand, obtain energy by oxidising iron and sulphur compounds.

One family of autotrophic bacteria that the team found within their biofilm samples is called Gallionellaceae. These bacteria corrode iron by oxidising it, leading to iron oxide deposits inside drainage pipes. Another finding was the detection of calcite deposits linked to microbial activity. This mineral buildup creates additional challenges for tunnel maintenance.

Günther Koraimann’s research provides valuable insight into the complex microbial ecosystems that exist within underground drainage systems. Their findings have practical implications for tunnel maintenance and the design of drainage systems. Through knowing which bacteria are responsible for biofilm formation, engineers can develop better strategies for preventing corrosion, blockages and mineral deposits, such as optimising drainage conditions to reduce biofilm accumulation.

Beyond tunnel maintenance, the team’s work also has implications for environmental monitoring. Their study provides valuable insights into global biogeochemical cycles, particularly the role of bacteria in carbon and methane cycling. These microbial processes have a direct impact on climate regulation, as they influence the storage and release of greenhouse gases from deep underground.