Simplifying microbial electrosynthesis reactor design.

Cloelle G S Giddings,Kelly P Nevin,Trevor Woodward

doi:10.3389/fmicb.2015.00468

Cloelle G S Giddings, Kelly P Nevin + Show 1 more

Open Access

https://doi.org/10.3389/fmicb.2015.00468

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Abstract

Microbial electrosynthesis, an artificial form of photosynthesis, can efficiently convert carbon dioxide into organic commodities; however, this process has only previously been demonstrated in reactors that have features likely to be a barrier to scale-up. Therefore, the possibility of simplifying reactor design by both eliminating potentiostatic control of the cathode and removing the membrane separating the anode and cathode was investigated with biofilms of Sporomusa ovata. S. ovata reduces carbon dioxide to acetate and acts as the microbial catalyst for plain graphite stick cathodes as the electron donor. In traditional ‘H-cell’ reactors, where the anode and cathode chambers were separated with a proton-selective membrane, the rates and columbic efficiencies of microbial electrosynthesis remained high when electron delivery at the cathode was powered with a direct current power source rather than with a potentiostat-poised cathode utilized in previous studies. A membrane-less reactor with a direct-current power source with the cathode and anode positioned to avoid oxygen exposure at the cathode, retained high rates of acetate production as well as high columbic and energetic efficiencies. The finding that microbial electrosynthesis is feasible without a membrane separating the anode from the cathode, coupled with a direct current power source supplying the energy for electron delivery, is expected to greatly simplify future reactor design and lower construction costs.

Highlights

Microbial electrosynthesis shows promise as a strategy for the production of transportation fuels and other organic commodities from carbon dioxide with renewable electricity as the energy source (Leang et al, 2012; LaBelle et al, 2014; Rosenbaum and Henrich, 2014)
Pure culture studies have demonstrated that a diversity of acetogens can accept electrons from negatively poised electrodes for the reduction of carbon dioxide to acetate with high columbic efficiencies (Nevin et al, 2010, 2011)
The results suggest that microbial electrosynthesis reactors can be simplified in this manner while maintaining high energetic efficiencies

Summary

Introduction

Microbial electrosynthesis shows promise as a strategy for the production of transportation fuels and other organic commodities from carbon dioxide with renewable electricity as the energy source (Leang et al, 2012; LaBelle et al, 2014; Rosenbaum and Henrich, 2014). The development of a genetic tool box for the acetogen Clostridium ljungdahlii, and the use of these tools to redirect carbon and electron flow, suggest that this necessary step in the development of commercially competitive microbial electrosynthesis can be met (Leang et al, 2012; Tremblay et al, 2013; Banerjee et al, 2014; Ueki et al, 2014). Potentiostat control over large electrode systems is impractical because it is energy intensive to maintain a fixed potential and the potentiostat has limited control in large-scale systems (Rosenbaum et al, 2011) Another concern is that the anode chamber and cathode chamber in previous microbial electrosynthesis reactors were separated with a membrane designed to permit ion flux between the chambers, while restricting oxygen diffusion. The results suggest that microbial electrosynthesis reactors can be simplified in this manner while maintaining high energetic efficiencies

Materials and Methods

Objective

Results and Discussion