Microbial electrochemical technologies (MET)

Electroactive biofilms: models for studying microbial interactions

• Organization of populations and microbial interactions in biofilms: role of major and minor taxa?

 

• Interactions between electroactive and fermentative bacteria: towards electro-fermentation (see below)

 

• From observation to action: ecological engineering in microbial electrochemical processes

 

• Examples: anodic volatile fatty acids oxydation, cathodic homoacetogenesis, cathodic nitrogen fixation

 

Figure 2: Different configurations of MET where organic matter is fed in the anodic chamber and degraded by electroactive bacteria while electrons are released at the anode [1]. (A) In Microbial Fuel Cells (MFC) electrons are consumed in the cathodic chamber using strong electron acceptors and the global process produces energy. (B) In Microbial Electrolysis Cells (MEC), the global process consumes energy to produce target molecules such as H2, CH4 or organic acids in the cathodic chamber. (C) example of lab-scale two-chamber reactor.

Electro-fermentation: use of electrodes to drive a fermentation process

Electro-fermentation (EF) is a novel process that consists of electrochemically controlling microbial fermentative metabolism with electrodes [2]. The electrodes can act as either electron sinks or sources and allow unbalanced fermentations. They can also affect the oxidation–reduction potential (ORP) of the medium.
Such electro-chemical control exerts significant effects not only on microbial metabolism and cellular regulation but also on interspecies interactions and the selection of bacterial populations in mixed microbial cultures. The research developed aim at understanding the mechanisms involved and using them in anaerobic bioprocesses.

Figure 3: Hypothetical mechanisms that can occur during anodic electro-fermentation (EF) [2].

Integration of MET in biorefinery

An interesting possible integration of MET in biorefinery is the coupling of a microbial electrolysis cell (MEC) with a dark fermentation (DF) process [3]. Our first results showed that coupling DF and MEC for organic wastewater treatment and/or by-products transformation constitutes not only a suitable but also a highly promising route for producing bio-H2 within the scheme of an environmental biorefinery.

Figure 4: Scheme of H2 production from agro-industrial wastewaters and by-products, by combining dark fermentation and microbial electrolysis in a two-step cascade process [3].

References

[1] Moscoviz, R. et al. (2019) Biorefinery, 511–34.  Springer International Publishing.
[2] Moscoviz, R. et al. (2016) Trends Biotechnol.
[3] Marone, A. et al. (2017) Int. J. Hygrogen Energ.