In situ Biogas Upgrading by CO2-to-CH4 Bioconversion

Abstract

Biogas produced by anaerobic digestion is an important renewable energy carrier. Nevertheless, the high CO2 content in biogas limits its utilization to mainly heat and electricity generation. Upgrading biogas into biomethane broadens its potential as vehicle fuel or substitute for natural gas. CO2-to-CH4 bioconversion represents one cutting-edge solution for biogas upgrading. In-situ bioconversion can capture endogenous CO2 directly from the biogas reactor, is easy to operate, and provides an infrastructure for renewable electricity storage. Despite these advantages, several intrinsic challenges need to be addressed to move in-situ upgrading technologies closer to applications at scale. This opinion article reviews the state-of-art of this technology and identifies some obstacles and opportunities of biological in-situ upgrading technologies for future development.

Temperature and Inoculum Origin Influence the Performance of Ex-Situ Biological Hydrogen Methanation

“…Two technologies can be used to perform the methanation reaction. The so-called "catalytic" methanation, based on the Sabatier reaction, is carried out using chemical catalysts such as nickel at high temperatures (250-450 • C) [6,7]. The biological methanation (also called biomethanation) is based on microorganisms, the conversion being operated at moderate temperatures and pressures • C and atmospheric pressure up to 10 bars, respectively) [8][9][10].…”

“…The biological methanation (also called biomethanation) is based on microorganisms, the conversion being operated at moderate temperatures and pressures • C and atmospheric pressure up to 10 bars, respectively) [8][9][10]. In addition, when performed on biogas issued from anaerobic digestion (AD) plants, biological methanation can be considered as a substitute of a CO 2 purifier through biogas upgrading [7,11].…”

“…Mechanistically, the biological methanation reaction corresponds to one of the last biological reactions of the anaerobic digestion process, as methanogenic archaea are the sole microorganisms able to convert hydrogen (H 2 ) and carbon dioxide (CO 2 ) into CH 4 [12]. The main advantage of the biological methanation process is the low energy cost if compared to catalytic methanation [7,13]. Since the CO 2 content in the AD biogas ranges usually between 25 and 48% [5], biological methanation is an adequate technology for biogas upgrading into biomethane (up to 98% of CH 4 ) [14].…”

“…Indeed, even if the temperature can modify the kLa through the modification of soluble gas diffusion coefficient and the viscosity of the medium, lowering the temperature of the reactor can increase drastically the solubility of H 2 . However, temperature affects also the carbon to CH 4 bioconversion pathway [7]. Under thermophilic conditions, hydrogenotrophic methanogens are more active [25], while homoacetogens are better adapted to lower temperatures [26].…”

Ex-situ biogas upgrading to methane and removal of VOCs in a system of zero valent iron and anaerobic granular sludge

“…However, as reported in recent studies (Jiang et al 2019;Bajracharya 2020;Prévoteau et al 2020) high capital and operating/maintenance costs and particularly the cost of the proton exchange membrane are the key limitations in the industrialization of microbial electrosynthesis. According to recent review (Fu et al 2020) biological biogas upgrading by CO 2 -to-CH 4 bioconversion depends on an accessible, available, and cost-effective H 2 . Despite the environmental bene ts currently in situ biological biogas upgrading by bioconversion of CO 2 into4 seems to be more expensive than physicochemical biogas upgrading and more research need to take place for optimization of this process (Fu et al 2020).…”