Microbial electromethanogenesis: a novel approach for biomethane enrichment

Abstract

Owing to the limited availability of conventional energy resources and their adverse environmental impacts, there is a need for sustainable, environmentally sound alternative energy sources. Biofuel production through biological processes has gained attention as an environmentally benign alternative fuel. Among various biological processes, anaerobic digestion is one of the oldest and most popularized for producing biogas as a promising future energy source. However, raw biogas cannot be used as a fuel for transportation or other applications because it contains non‐calorific gases, such as CO ₂ , which lowers its energy density. Therefore, upgrading biogas by removing CO ₂ is necessary to increase its CH ₄ content. Microbial electromethanogenesis is a potential technique for converting CO ₂ to CH ₄ that not only upgrades biogas to biomethane but also increases its energy density, ultimately enhancing its calorific value. In this technique, methane is produced by reducing CO ₂ with biocatalysts under a low imposed potential. It can be used to upgrade biogas to biomethane, offering many advantages, such as efficient conversion of waste CO ₂ into energy products like CH ₄ , which makes the process environmentally friendly, with very low power consumption, a high methane content in the upgraded biogas, and economic benefits. The present study focuses on the operation, scaling‐up, techno‐economic analysis, and future scope of microbial electromethanogenesis for biogas enrichment to improve its efficiency. As a result of techno‐economic assessments, electrode materials can account for approximately 59% of total capital expenditure, while electricity may constitute up to 69% of operating expenditure, demonstrating the importance of electrode costs and electricity demand to process economics. Model‐based analyses have further indicated positive economic performance at electricity prices of ≤€0.045 kWh ⁻¹ under the evaluated process assumptions. Overall, the technology presents an excellent opportunity to upgrade biogas and valorize CO ₂ , but further improvements in efficiency, reactor design, material durability, microbial stability, and system economics are needed to progress from pilot‐scale demonstrations to commercially viable biomethane production.