Deciphering the electron transfer mechanisms for biogas upgrading to biomethane within a mixed culture biocathode

Abstract

a Biogas upgrading is an expanding field dealing with the increase in methane content of the biogas to produce biomethane. Biomethane has a high calorific content and can be used as a vehicle fuel or directly injected into the gas grid. Bioelectrochemical systems (BES) could become an alternative for biogas upgrading, by which the yield of the process in terms of carbon utilisation could be increased.The simulated effluent from a water scrubbing-like unit was used to feed a BES. The BES was operated with the biocathode poised at À800 mV vs. SHE to drive the reduction of the CO 2 fraction of the biogas into methane. The BES was operated in batch mode to characterise methane production and under continuous flow to demonstrate its long-term viability. The maximum methane production rate obtained during batch tests was 5.12 AE 0.16 mmol m À2 per day with a coulombic efficiency (CE) of 75.3 AE 5.2%.The production rate increased to 15.35 mmol m À2 per day (CE of 68.9 AE 0.8%) during the continuous operation. Microbial community analyses and cyclic voltammograms showed that the main mechanism for methane production in the biocathode was hydrogenotrophic methanogenesis by Methanobacterium sp., and that electromethanogenesis occurred to a minor extent. The presence of other microorganisms in the biocathode, such as Methylocystis sp. revealed the presence of side reactions, such as oxygen diffusion from the anode compartment, which decreased the efficiency of the BES. The results of the present work offer the first experimental report on the application of BES in the field of biogas upgrading processes.

On the Edge of Research and Technological Application: A Critical Review of Electromethanogenesis

“…Particularly, the production of molecular hydrogen (Equation (4)), previous to methane production, was observed to enhance the methane yield through the activity of hydrogenotrophic methanogens found in biocathodes [13]. Such claim was supported by other authors, Batlle-Vilanova et al suggested that only a small amount of methane is directly produced via accepting electrons from the electrode, while most of the production comes from biologically generated hydrogen (Equation (4)) in the biocathode surface followed by hydrogenotrophic methanogenesis [14]. Therefore H 2 is nowadays considered to be the main electron transfer molecule for bioelectrochemical methane production, especially at low applied cathode potentials [15].…”

Anion vs cation exchange membrane strongly affect mechanisms and yield of CO2 fixation in a microbial electrolysis cell

“…From an economical point of view, however, CO 2 removal is feasible only for biogas produced in large-plants unless novel low cost upgrading approaches are developed. In this context, microbial electrochemical technology has been recently proposed as an innovative and promising tool to upgrade the AD biogas [14][15][16][17].…”

Design, Operation, Modeling and Grid Integration of Power-to-Gas Bioelectrochemical Systems

“…In the present study, an innovative power-to-gas technology, based on a bioelectrochemical system (BES), was developed for renewable energy surplus storage in the form of biomethane (Figure 1). The term biomethane defines a biogas rich in methane (>95% v/v), obtained from a biological source (like wastewater or sludge), that can be directly used as vehicle fuel or injected into the gas pipeline [2]. The biomethane can be obtained from biogas by different upgrading systems, being water scrubbing the most common one.…”

“…These can be obtained in both double-chamber (where anode and cathode are separated by an ionic exchange membrane) or single-chamber BES reactors. The former configuration allows to increase the Coulombic efficiency of the process (ratio of electrons recovered as methane, versus the amount provided as current) but at higher costs due to membrane presence, causing an increase of the internal resistance [2]. The latter configuration, although less efficient, is cheaper to build and operate, and can be easily scaled-up [9].…”