Niels Burzan | EPFL Graph Search

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Growth and persistence of an aerobic microbial community in Wyoming bentonite MX-80 despite anoxic in-situ conditions

Rizlan Bernier-Latmani, Niels Burzan, Manon Frutschi, Roberta Murad Lima

Microbial activity has the potential to enhance the corrosion of high-level radioactive waste disposal canisters, which, in the proposed Swiss deep geological repository, will be embedded in bentonite and placed in the Opalinus Clay rock formation (OPA). Twelve stainless-steel cylindrical vessels (referred to as modules) containing bentonite were deployed in an anoxic borehole in OPA for up to 5.5 years. Carbon steel coupons were embedded in the bentonite. Individual modules were retrieved after 1, 1.5, 2.5 and 5.5 years. Enumeration of aerobic and anaerobic heterotrophs and sulfate-reducing bacteria (SRB) revealed microbial growth for 1.5 years followed by a decline or a stagnation in microbial viability. It was surprising to observe the growth of aerobic heterotrophs followed by their persistent viability in bentonite, despite the nominally anoxic conditions. In contrast, SRB numbers remained at very low levels. DNA-based amplicon sequencing confirmed the persistence of aerobes and the relatively low contribution of anaerobes to the bentonite microbiome. Bentonite dry density, in-situ exposure time, and bioavailable trapped oxygen are observed to shape the bentonite microbial community in the clay.

2022

Growth and viability of microorganisms in bentonite and their potential activity in deep geological repository environments

Niels Burzan

Radioactive waste is among the most dangerous anthropogenic waste and its safe disposal is a challenging multi-generational task. Many nations have sought for the peaceful application of nuclear fission for the reliable production of electric energy to power their societies. The increasing volumes of radioactive waste generated are, however, proving an increasingly urgent problem to tackle. Deep geological disposal is deemed our best option for the safe long-term disposal of radioactive waste. Different host rocks are being considered for deep geological disposal, depending on the nation's geology. Switzerland favours the Opalinus Clay Formation due to its very low hydraulic conductivity and good radionuclide retention capabilities. Microorganisms in the deep subsurface are active and must be considered as their activity will influence a deep geological repository for radioactive waste. On one hand, the microorganism's activity represents a safety concern due to the possibility of enhanced corrosion, when considering the metallic waste canister encapsulating spent fuel from nuclear power plants. In other cases, however, they can contribute to the safety of a deep geological repository, when considering the gas balance of a Swiss low- and intermediate-level repository. Anoxic corrosion of metallic radioactive waste poses risks to the structural integrity of the host rock. Harnessing the activity of naturally occurring microorganisms at a safe distance from the waste itself can result in the net reduction of gases and thus their activity can be viewed as beneficial and worth exploring. In this thesis, both the positive and negative aspects of the microbial presence are explored. Wyoming bentonite is a back-fill material and an important engineered barrier system for spent nuclear fuel and high-level waste. Within the framework of an in-situ corrosion experiment, the presence and growth of microorganisms in Wyoming bentonite are investigated. The results show that the activity of corrosion enhancing sulfate-reducing bacteria in Wyoming bentonite is inhibited during the critical bentonite saturation phase but other microorganisms were able to grow. The second in-situ research project explores the potential implementation of a microbial gas sink, a natural biofilm composed of hydrogen-oxidizing sulfate-reducing bacteria and methanogenic archaea. Indeed, under the right conditions, a microbial gas sink can fulfil its intended design purposes and consume all hydrogen-gas evolving from the anoxic corrosion of the waste. This thesis contributes to our understanding of the near-field processes of a Swiss radioactive waste repository within the Opalinus Clay Formation through the contribution of experimental insight obtained under in-situ conditions.

EPFL2021

H2-fuelled microbial metabolism in Opalinus Clay

Rizlan Bernier-Latmani, Aislinn Ann Boylan, Niels Burzan, Luca Loreggian, Carla Perez Mon

In Switzerland, the Opalinus Clay formation is considered the most likely host rock for a deep geological repository for nuclear waste. In deep geological repositories, H2 is expected to be the most abundant gas formed from the degradation of waste and from metal corrosion. The microbial community present in Opalinus Clay is capable of utilizing H2 as an electron donor and sulfate as an electron acceptor to produce hydrogen sulfide. This could be problematic due to its potential for increasing the corrosion of metal waste canisters containing radioactive waste, however, the possible impacts of these processes on the clay rock have not been fully investigated. In this study, a series of microcosm experiments were set-up containing Opalinus Clay and porewater from the Mont Terri underground research laboratory (Switzerland) as an inoculum. Uninoculated microcosms were established to investigate abiotic processes. In the presence of clay, a higher aqueous sulfate concentration was detected than in those with only porewater present and this concentration decreased over time in the inoculated experiments. However, there was no evidence of hydrogen sulfide production in the aqueous phase. In all experiments with clay, there was an increase in aqueous Fe2+ concentrations with the highest concentrations found in uninoculated experiments. The sulfur speciation of the Opalinus Clay was analysed and the results of the inoculated sample suggested that hydrogen sulfide reacted with Fe2+, precipitating iron sulfide minerals. After the incubation period, the microbial community was dominated by the sulfate-reducing Desulfobulbaceae family. The study suggests that H2-fuelled, microbially-mediated sulfate reduction can affect the mineral composition within the Opalinus Clay due to the precipitation of iron sulfide minerals. These precipitation reactions may enhance the long-term integrity of the repository by removing corrosive hydrogen sulfide from solution when sufficient Fe2+ is available and so protecting the canisters containing the nuclear waste.

2019