Microbial activity at the Bentonite barrier in a deep geological nuclear waste repository

Project Information

MicroBent

Grant agreement ID: 101060228

DOI

10.3030/101060228

Project closed

EC signature date 4 May 2022

Start date 16 May 2022

End date 15 March 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 201 714,48

Coordinated by

UNIVERSIDAD DE GRANADA
Spain

Periodic Reporting for period 1 - MicroBent (Microbial activity at the Bentonite barrier in a deep geological nuclear waste repository)

Reporting period: 2022-05-16 to 2025-03-15

Summary of the context and overall objectives of the project

Management of nuclear waste is a serious worldwide environmental problem all. Deep geological repositories have been internationally proposed as the safest option for the disposal of these hazardous materials. The concept is based on a multi-barrier storage system with waste containers, surrounded by a bentonite buffer buried deeply within a stable geological formation. The bentonite formations in Almeria were characterized as a bentonite buffer reference material. However, few studies have described the influence of the microbes in the repository under in situ conditions, although its safety can be compromised not only by physical and chemical factors, but also by biogeochemical activity.
Therefore, the hypothesis to be tested in this project is that indigenous microorganisms may play an important role for the safe disposal of nuclear waste. The main objective of this proposal is to study the microbial diversity and activity of the bentonite buffer under in situ conditions for a repository of radioactive waste.

To address these points the following objectives will be carried out under in situ conditions:
1) to characterize the mineralogical and geochemical composition of the bentonite buffer
2) to determine the microbial of the incubated bentonite buffer
3) to determine the microbial activity of the incubated bentonite buffer.

This project will extend the state-of-the-art for nuclear waste repositories by identifying active microorganisms in compacted bentonites and natural deep groundwaters and active microbial metabolic pathways. These vital questions need to be addressed to ensure the safety of the deep geological repository of nuclear waste, but also for other biotechnological uses like bioremediation of contaminated sites.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The multi- and interdisciplinary aspects of MicroBent include the use of molecular biology to describe microbial populations and metabolisms in a repository system through metaomics, and directly applied to the storage of highly radioactive waste. MicroBent will bridge the knowledge gaps (Table 1) in current areas and enhance tools to determine microbial activity. Applied knowledge of microbial population and their active metabolic pathways will benefit other scientific areas dependant on microbiomes (i.e. bioremediation industry, biotechnology and astrobiology).

The main objectives are:

1. Geochemical and mineralogical characterization of the groundwaters and bentonites incubated under in situ conditions.
2. Identify the microbial community of the incubated compacted bentonites by culture-dependent methods
3. Characterize the isolate metabolisms and their influence in the DGR.

Main achievements:

- Geochemical analysis confirmed the groundwaters chemical stability and neutral pH. However, they had different chemical compositions and could be characterized with regard to origin and age. The bentonite composition was dominated by SiO2, plus calcium and magnesium oxides, with light variations after the incubation.
- The mineralogy of the bentonite samples was dominated by smectites (calcium montmorillonite) and plagioclases, combined with minor quantities of quartz, cristobalite and mica. Newly formed Fe minerals were identified after the in situ incubation.
- A total of 12 microorganisms were isolated from the enrichments and identified by 16S rRNA gene sequencing, affiliated to Firmicutes and Proteobacteria phyla, with metabolisms involved in sulfate reduction plus iron oxidation coupled to nitrate reduction.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

- Microbial populations are influenced by the different groundwaters, which were very stable based on their geochemical parameters.
- Bentonite mineralogical composition seems to be modified by incubation under real repository conditions. Newly formed minerals, probably generated by biological activity, were identified.
- Iron- and sulfate-reducing bacteria can be identified by culture-dependent methods from bentonites incubated under in situ repository conditions.
- This highlights the need to further investigate microbial processes occurring deep underground to ensure the integrity and safety of future deep geological repositories of highly radioactive waste.

MicroBent logo