Biological Aspects, Advancements and Techno-Economical Evaluation of Biological Methanation for the Recycling and Valorization of CO2

Abstract

Nowadays, sustainable and renewable energy production is a global priority. Over the past decade, several Power-to-X (PtX) technologies have been proposed to store and convert the surplus of renewable energies into chemical bonds of chemicals produced by different processes. CO2 is a major contributor to climate change, yet it is also an undervalued source of carbon that could be recycled and represents an opportunity to generate renewable energy. In this context, PtX technologies would allow for CO2 valorization into renewable fuels while reducing greenhouse gas (GHG) emissions. With this work we want to provide an up-to-date overview of biomethanation as a PtX technology by considering the biological aspects and the main parameters affecting its application and scalability at an industrial level. Particular attention will be paid to the concept of CO2-streams valorization and to the integration of the process with renewable energies. Aspects related to new promising technologies such as in situ, ex situ, hybrid biomethanation and the concept of underground methanation will be discussed, also in connection with recent application cases. Furthermore, the technical and economic feasibility will be critically analyzed to highlight current options and limitations for implementing a sustainable process.

Assessment of the in situ biomethanation potential of a deep aquifer used for natural gas storage

“…Prokaryotic taxonomic diversity was studied at the end of incubation in biotic assays with a gas phase consisting of H 2 or H 2 /CO 2 . These biomethanation conditions strongly selected for microbial communities, as previously reported (Bellini et al 2022 ). In order to test a large number of conditions, it was decided not to use culture replicates for taxonomic diversity analyses, which can make it difficult, if not impossible, to interpret the evolution of complex microbial communities.…”

“…Indeed, deep aquifers are found all over the globe in sedimentary basins, and those in the first 2 km of depth could reach a cumulative volume of 22.6 million km 3 (Gleeson et al 2016 ). The use of these storage sites would be conditional on the presence of a decarbonated H 2 production area (renewable and nuclear), an accessible source of CO 2 , ideally captured from industry or even the atmosphere (Gutknecht et al 2018 , Hou et al 2022 ), and a geological storage reservoir equipped with injection and production wells, as well as a gas network enabling biomethane distribution (Bellini et al 2022 ). By overcoming a number of scientific hurdles, these deep, secure sites would represent a biomethanation potential at a scale several times larger than that of conventional catalytic or biological methanation reactors due to the very large reservoir volumes (Molíkova et al 2022 , Vítĕzová et al 2023 ).…”

“…In 2021, a study on the Olla Oil Field, which was operated using CO 2 injection (CO 2 -EOR) until 1986, showed a conversion of 13%–19% of CO 2 into CH 4 via methanogenesis (Tyne et al 2021 ). At present, three projects are attempting to prove the feasibility of biomethanation in depleted hydrocarbon reservoirs and are being tested under real conditions: the Hychico-BRGM pilot project in Argentina, the Underground Sun Conversion—Flexible Storage Project, and the Bio-UGS Project “Biological conversion of carbon dioxide and hydrogen to methane in porous underground gas storage facilities: Analysis of underground biomethanation potential” (see reviews by Strobel et al 2020 , Dopffel et al 2021 , Bellini et al 2022 ).…”

Biogeochemical characterization of four depleted gas reservoirs for conversion into underground hydrogen storage

“…Loss of H 2 and energy value (about 17%–18%) can be potentially caused by the activation of the methanation process carried out by hydrogenotrophic methanogenic archaea, which can oxidize 4 moles of H 2 and reduce 1 mole of CO 2 to produce 1 mole of CH 4 (Equation ; Bellini et al, 2022; Ebigbo et al, 2013; Gniese et al, 2014; Hagemann et al, 2016; Panfilov, 2010; Toleukhanov et al, 2015; Wagner & Ballerstedt, 2013).…”

“…These two aspects are strictly interconnected, as microbial metabolisms in natural environments are influenced and shaped by the presence of different arrays of nutrients (e.g., carbon sources and metal ions) and by the physico‐chemical parameters characterizing the field (e.g., temperature, pressure, pH, salinity), which select organisms capable of sustaining life in such environments. The chemical characterization of natural habitat provides information regarding the presence and availability of nutrients/inhibitors potentially involved in indigenous microbial metabolisms (Bellini et al, 2022; Haddad et al, 2022; Romero‐Güiza et al, 2016). Similarly, as explained above, understanding the microbial biodiversity inhabiting the deep underground is fundamental to the success of UHS.…”