Bringing High-Rate, CO₂-Based Microbial Electrosynthesis Closer to Practical Implementation through Improved Electrode Design and Operating Conditions

Abstract

The enhancement of microbial electrosynthesis (MES) of acetate from CO2 to performance levels that could potentially support practical implementations of the technology must go through the optimization of key design and operating conditions. We report that higher proton availability drastically increases the acetate production rate, with pH 5.2 found to be optimal, which will likely suppress methanogenic activity without inhibitor addition. Applied cathode potential as low as -1.1 V versus SHE still achieved 99% of electron recovery in the form of acetate at a current density of around -200 A m(-2). These current densities are leading to an exceptional acetate production rate of up to 1330 g m(-2) day(-1) at pH 6.7. Using highly open macroporous reticulated vitreous carbon electrodes with macropore sizes of about 0.6 mm in diameter was found to be optimal for achieving a good balance between total surface area available for biofilm formation and effective mass transfer between the bulk liquid and the electrode and biofilm surface. Furthermore, we also successfully demonstrated the use of a synthetic biogas mixture as carbon dioxide source, yielding similarly high MES performance as pure CO2. This would allow this process to be used effectively for both biogas quality improvement and conversion of the available CO2 to acetate.

How to Sustainably Feed a Microbe: Strategies for Biological Production of Carbon-Based Commodities with Renewable Electricity

“…However, studies with a new type of cathode material have greatly accelerated the rates of in situ H 2 production at the cathode while simultaneously selecting for a microbial community that can effectively consume the H 2 as fast as it can be produced (Jourdin et al, 2016a,b). The breakthrough in cathode design was to fix carbon nanotubes on the cathode surface (Jourdin et al, 2015).…”

Bio-Electrochemical process for Metal and Sulfur Recovery from Acid Mine Drainage

“…). MWCNT-RVC was shown to enhanced microbial adhesion, resulting in the highest acetate production rate reported to date for MES (Jourdin et al 2016a). …”

“…Carbon electrode materials are a key parameter that affects biofilm attachment and selective microbial retention. Several three-dimensional carbon electrodes have been proposed in order to increase microbial-surface interaction due to their high conductivity, good chemical stability and smooth surface (Jourdin et al 2015a;Jourdin et al 2016a;Marshall et al 2012;Virdis et al 2011). Although some research has been carried out on carbonbased surface as electron material for autotrophic sulfate removal (Su et al 2012;Coma et al 2013;Luo et al 2014;Teng et al 2016;Blázquez et al 2016), no single study exists which described autotrophic sulfate reduction using three-dimensional coating multiwalled carbon nanotubes on reticulated vitreous carbon (MWCNT-RVC) as the electrode material.…”

“…After reaching steady-state of autotrophic sulfate reduction in a period of four months of enrichment, the biocathode chamber was connected to TOGA sensor (Gapes & Keller 2001;Pratt et al 2003) (see Figure 6.1 for a schematic layout), to undertake realtime quantification of gas production and consumption, including hydrogen, methane and carbon dioxide (Virdis et al 2009;Zhou et al 2013;Freguia et al 2007;Jourdin et al 2016a). …”

“…As shown in Figure 6.1, the gas was dried after passing through a refrigerator and an air-drying column prior to analysis by the mass spectrometer. Calibration of the mass spectrometer was done according to Pratt et al 2003 andJourdin et al 2016a. After the sulfate-reducing biocathode was linked to the TOGA setup, a scan range from -0.2 to -1.2 V vs. SHE was applied using linear sweep voltammetry (LSV) at a scan rate of 0.1 mV s -1…”