Simultaneous Biogas Upgrading and Desulfurization Using a Microbial Electrosynthesis System with Optimized Electrodes and Membrane Selection

Abstract

Biogas upgrading based on the principle of the microbial electrosynthesis (MES) system offers a promising avenue for biogas upgrading. Here, we explored 4 different combinations of cathode and membrane materials to optimize MES for biogas upgrading. MES equipped with a stainless steel cathode and Nafion 117 membrane (designated as MES-2) demonstrated optimal performance, achieving a maximum methane production of 268.5 ± 19.5 L_methane/m_cathode³ with a bicarbonate medium. Furthermore, MES-2 showed superior performance with a CO₂-rich gas (70% CO₂ and 30% N₂), achieving 100% CO₂ conversion to methane conversion after 3 days of gas recirculation. When testing different biogas sources (synthetic and real anaerobic digestion biogas), MES-2 also consistently provided >99% methane content within a relatively short time (<3 days) of biogas recirculation. Additionally, H₂S content was significantly reduced from 214 ppmv to <1 ppmv, enabling the upgraded biogas to be widely utilized in various applications. The microbial community analysis indicated that this outcome was primarily due to the substantial growth of chemolithoautotrophic sulfide-oxidizing bacteria, such as Thiobacillus, which likely converted sulfide to elemental sulfur and/or sulfate. This study underscores the potential of MES as a highly effective and uniquely adaptable technology for biogas upgrading and desulfurization, promoting sustainable energy practices.