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.

E-materials become e-waste once they have been discarded without the intent of reuse. Due to its rich content of metals, among which many are Critical Raw Materials (CRMs), e-waste can be considered an urban mine to exploit and valorise. Common metal refining is performed by energy-intensive processes frequently based on the use of fossil fuel. Bio-metallurgy is a promising alternative for e-waste valorisation based on biological routes of specialised microorganisms able to leach solid-containing metals. Because of the physiology of these microorganisms, microbial leaching can be economically feasible, besides being an environmentally sustainable process. Like Bacteria and Fungi, Archaea are also capable of metal leaching activity, though their potential is underestimated. Among them, the extremophiles are the most studied and applied in the field of metal recovery, while mesophilic species are less common but still of high interest. Here we provide the state of industrial application of bio-metallurgy and report on the state of the art of Archaea exploitation in metal recovery from e-waste. Moreover, we give a special highlight to methanogenic archaea, which are able to convert CO₂ into methane in order to highlight the potential for the valorisation of CO₂-rich industrial streams generated by key processes (i.e., anaerobic digestion, concrete, and steel production) in CH₄ for gas grid distribution, while making metals content in e-waste available again as raw material.