Electrochemical and microbial monitoring of multi-generational electroactive biofilms formed from mangrove sediment

Evolution and interaction of microbial communities in mangrove microbial fuel cells and first description of Shewanella fodinae as electroactive bacterium

Understanding exoelectrogenic bacteria mechanisms and their interactions in complex biofilm is critical for the development of microbial fuel cells (MFCs). In this article, assumptions concerning the benefits of the complex sediment microbial community for electricity production were explored with both the complex microbial community and isolates identified as Shewanella. Analysis of the microbial community revealed a strong influence of the sediment community on anodes and electrolytes compared to that of only water. Moreover, while Pelobacteraceae-related genera were dominant in our MFCs instead of Desulfuromonas and Geobacter as usually reported, the electroactive Shewanella algae and Shewanella fodinae were isolated and cultivated from the anodic biofilm. S. fodinae, described for the first time as an electroactive bacterium to the best of our knowledge, led to a maximal current density of 3.6 A/m² set as 0.3 V/SCE in a three-electrode set-up fed with lactate. S. algae, in a complex medium containing several available substrates, showed several preferential oxidative behaviors including a diauxic behavior. In pure culture and under our conditions, S. fodinae and S. algae were not able to use acetate as a sole electron donor. However, their presence in our acetate-fed MFCs and the adaptive behavior of S. algae hint a syntrophic interaction between the bacteria to optimize the use of the substrate in a complex environment.

Enrichment of Clostridia enhances Geobacter population and electron harvesting in a complex electroactive biofilm

Current research on microbial fuel cell or microbial electrolysis cell dealt with finding new electroactive bacteria and understanding the mechanisms of electronic exchange. Complex consortia allowed to obtain better performances than pure cultures in part thanks to inter-species cooperation. However, the role of each bacterium in a complex biofilm in the electron harvest on an electrode remains unclear. Thus, we combined electrochemical monitoring of electron exchange and high throughput sequencing analysis in order to describe the bacterial composition and the electroactive performance of mangrove mud biofilms. In this study, secondary electroactive biofilms were formed on carbon electrodes from Desulfuromonas-dominated inoculum of pre-formed bioanodes. The performances and the Desulfuromonas-dominated profile were the same as those of primary bioanodes when the planktonic community was conserved. However, a Clostridium enrichment allowed to restore the performance in maximal current densities promoting an increase of Geobacter population, becoming the most dominant group among the Deltaproteobacteria, replacing Desulfuromonas. These results highlight a positive collaboration between Clostridium and Geobacter spp. helping a bacterial population to achieve with the depletion of their environment. Our study provides new insight into relationships between dominant electroactive bacteria and other bacteria species living in an organic matter-rich environment as mangrove sediments.

Scratching and transplanting of electro-active biofilm in fruit peeling leachate by ultrasound: re-inoculation in new microbial fuel cell for enhancement of bio-energy production and organic matter detection

OBJECTIVE

An electro-active biofilm of Fruit Peeling (FP) leachate was formed onto the Carbon Felt (CF) bio-anode in a Microbial Fuel Cell (MFC), after functioning for a long time. The electro active-biofilm thus formed was then scratched by ultrasound and re-inoculated in a new leachate to be transplanted onto the bio-anode. This procedure allowed the microbial electron charge transfer and therefore the enhancement of the bio-energy production of the fuel cell.

RESULTS

By using the repetitive mechanical biofilm removal, re-suspension and electrochemically facilitated biofilm formation, the voltage was substantially increased. In effect, the voltage of the 1st G of biofilm, rose gradually and reached its maximum value of 65 mV after 10 days. Whilst the 2nd generation allowed to obtain the maximum voltage 276 mV and without any lag time. The DCO abatement using the 1st G biofilm was 68% greater than the 3rd G 26%. Besides, the electrochemical impedance spectroscopy characterization and cyclic voltammetry of bio-anode with 2nd G biofilm confirmed the ability of electro-active biofilm formation on a new support. The biofilm transplanted showed thus greater kinetic performance, with reduced lag time demonstrating the interest of the selection that took place during the formation of successive biofilms.

CONCLUSIONS

Despite the transplantation of the electro-active biofilm onto the bio-anode, the MFC still produced relatively lower power output. Nevertheless, it has been tested successfully for monitoring and detecting the oxidation of sodium acetate substrate in the very wide concentration range 0.0025-35 g/l.