Biogeochemical valorization of geothermal dissolved gases for energy production without carbon emission

Framework of the thesis: the MiningBrines Project 

MiningBrines (Multidisciplinary Integration and Networking for INcreased sustainability and multi-resources valorization of Geothermal Brines) offers an innovative doctoral training program to address Europe's strategic need for sustainable access to critical raw materials (CRM), energy gases (EG) and renewable energies.

19 Doctoral Candidates (DCs) will receive interdisciplinary training in geosciences (Work Packages 2 and 3), biogeochemistry (Work Package 4), artificial intelligence (AI) (Work Package 5), and socio-economic analysis (Work Package 6), equipping them with advanced skills in reservoir modeling, machine learning, advanced oxidation processes (AOP), and microbial enhanced recovery. DCs will also develop intuitive fluid chemistry modeling workflows and innovative multi-criteria intelligent decision support tools, preparing them to drive innovation in geothermal brine mining while collaborating with academic and industrial partners on practical solutions. 

MiningBrines introduces novel techniques to maximize geothermal multi-resource recovery while minimizing environmental impact. Key innovations include microbial-driven CRM recovery, customized AOP workflows, scalable AI models, and decision support tools that consider technological, economic, and societal aspects. These advances aim to reduce the environmental footprint of resource extraction and align with the sustainability goals of the EU Green Deal.  

MiningBrines supports the EU's Critical Raw Materials Act by combining CRM and EG recovery with renewable energy production and circular economy principles, reducing Europe's import dependency and strengthening resilience. In addition, MiningBrines emphasizes collaborative education to meet the growing demand for skilled professionals capable of transforming geothermal multi-resources into a key driver of Europe's green transition. 

The impact of MiningBrines goes beyond scientific advances, fostering a skilled workforce for academic and industrial sectors, while establishing Europe as a global leader in sustainable resource management. 

MiningBrines promotes public awareness of the multiple benefits of geothermal energy, setting a standard for green industrial practices and long-term strategic autonomy. 

DC09 Research Project Description 

Objectives

The geothermal fluids at Draškovec (Croatia) contain dissolved gases, the main ones being methane (CH4) and carbon dioxide (CO2). With the aim to improve the energy efficiency of the geothermal doublet, the main objective of the thesis is to control and promote the conversion reaction of dissolved CO2 into CH4 through microbiological processes in a surface bioreactor, in which the microorganisms would ideally be indigenous (derived from the geothermal fluid) or selected from existing strain bank. The reservoir pressure and temperature conditions (up to 250 bar and 100 °C), together with those associated with geothermal operation (lower pressure and temperature), will critically influence the microbial conversion of CO₂ into CH₄. Therefore, detailed knowledge of the needs of microorganisms and operating conditions, including nutrient supply, is necessary to control the conversion of CO2 into CH4. 

The second objective focuses on the impact of re-injecting CO₂ produced by the combustion of CH₄ on microbial communities and their activity. It will also involve studying the fate of this CO₂ and the possibility of its mineralization through biogeochemical processes. 

Several scientific questions arise in the context of this thesis, which the recruited student will have to address:  

• What microbial communities live in the extreme conditions of the reservoir?  

• What are the physiological requirements of methanogenic microorganisms to produce methane from CO₂?  

• What will be the impact of CO₂ reinjection on deep microbial ecosystems and chemical balances?  

• What microbial processes could contribute to CO₂ mineralization in the reservoir?  

• How can biological processes be integrated into a geothermal doublet system?  

• What ancillary processes may accompany the conversion of CO₂ to CH₄? 

Methods

The first task of the PhD candidate will be to complete the geochemical and microbiological knowledge of the Draškovec geothermal reservoir. This will notably involve carrying out one or more water and rock sampling campaigns in order to analyze their composition and identify the microorganisms present. The objective will also be to collect water for future laboratory experiments. This work will be conducted in close collaboration with HGI (the Croatian Geological Survey), historically involved in the study of the site, and AATG, the company that will operate the geothermal doublet. In particular, a five-month secondment at AATG is planned to facilitate exchanges. This characterization work will also be carried out in coordination with another PhD project within the program (DC4), whose objective is to characterize the effect of CO₂ injection on reservoir geochemistry. In parallel with this first task, the candidate will identify, through literature review and commercial sources, methanogenic microorganisms capable of growing under the temperature, pressure, and salinity conditions of the site and the geothermal process.

The second stage of the PhD will consist of characterizing in the laboratory the ability of the different identified microorganisms (native or non-native) to produce methane under the environmental conditions of the reservoir and the geothermal process, taking into account the three main metabolic pathways potentially involved in methanogenesis. Based on the initial results, only one or two strains will be selected for in-depth study. The aim will be to understand their nutrient requirements and determine the impact of different experimental conditions (pH, temperature, salinity, etc.) on methane production rates. The work will also seek to identify metabolic pathways enabling CO₂ biomineralization, such as ureolysis. A four-month secondment at GFZ, at the same time as DC10 (which focuses on CO₂ biomineralization through ureolysis), is planned to address this topic.

The final stage of the PhD will consist of consolidating the two major concepts, namely CO₂-to-CH₄ conversion and CO₂ reinjection. Depending on the progress of research on the CO₂-to-CH₄ conversion process, a mini-pilot unit could be installed on site. In addition, the biogeochemical processes occurring during methanogenesis and after CO₂ reinjection could be modeled using geochemical and reactive transport simulation codes. The PhD candidate will again be able to rely on the work of DC4 as well as that of other doctoral candidates working on modeling. The ultimate goal is to assess the feasibility of integrating these research outcomes under real geothermal operating conditions. For this reason, the final three-month secondment of the PhD will take place at AATG, which is best positioned to address operational constraints.

Expected Results

The thesis is expected to provide a detailed characterization of microbial communities inhabiting deep geothermal systems and to define the physiological constraints governing biological CO₂-to-CH₄ conversion. It will establish operational parameters for optimizing methanogenesis in a surface bioreactor and quantify the effects of pressure, temperature, and nutrient supply on methane production efficiency. The research will further investigate and identify potential pathways for CO₂ bioprecipitation after its reinjection subsequent to methane combustion. This thesis will open innovative prospects for coupling deep geothermal energy, CO₂ sequestration, and renewable gas production by integrating microbial processes into existing energy infrastructures. 

More details and application instructions are available at: https://euraxess.ec.europa.eu/jobs/410970

BRGM is France’s leading public institution for Earth Science applications for the management of surface and sub-surface resources with a view to sustainable development.

Its work contributes to the sustainable development of territories, taking into account all associated risks, and to the optimal use of subsurface resources and properties.

Required Qualifications: 

Ability to design and carry out experimental laboratory tests and to conduct fieldwork

Strong background on microbiology and geochemistry

The ability to work effectively in a team on multidisciplinary topics

Strong communication skills to present and promote research results

Excellent command of spoken and written English (mandatory) 

Desirable Skills: 

Experience conducting experiments under anoxic conditions and/or under controlled pressure and temperature conditions

Techniques for the characterization of microorganisms, particularly DNA-based methods (PCR, sequencing)

Bioinformatic and statistical analysis of community DNA data and field-related datasets

Knowledge of water and gas analysis techniques