Characterization of Anaerobic Biofilms Growing on Carbon Felt Bioanodes Exposed to Air

Raúl M Alonso,Adrián Escapa,Guillermo Pelaz,Antonio Morán,María Isabel San-Martín

doi:10.3390/catal10111341

Abstract

The role of oxygen in anodic biofilms is still a matter of debate. In this study, we tried to elucidate the structure and performance of an electrogenic biofilm that develops on air-exposed, carbon felt electrodes, commonly used in bioelectrochemical systems. By simultaneously recording the current density produced by the bioanode and dissolved oxygen concentration, both inside and in the vicinity of the biofilm, it was possible to demonstrate the influence of a protective aerobic layer present in the biofilm (mainly formed by Pseudomonas genus bacteria) that prevents electrogenic bacteria (such as Geobacter sp.) from hazardous exposure to oxygen during its normal operation. Once this protective barrier was deactivated for a long period of time, the catalytic capacity of the biofilm was severely affected. In addition, our results highlighted the importance of the material’s porous structure for oxygen penetration in the electrode.

Highlights

The term microbial electrochemical technologies (METs) covers a group of bio-based electrochemical devices that hold great potential for practical applications in the fields of bioremediation and energy production/management [1]
Most of these electrogenic microorganisms can carry out their life cycle forming biofilms on the surface of the electrodes [3,4], where they benefit from favourable physical–chemicalenvironments and useful trophic relationships
In the biofilm vicinity, which has been amplified in Figure 3, we found decline, almost linearly, which is indicative that the probe is entering the at least three sub-regions that can be distinguished by changes to the shape of the dissolved oxygen (DO) concentration diffusion boundary layer (DBL)

Summary

Introduction

The term microbial electrochemical technologies (METs) covers a group of bio-based electrochemical devices that hold great potential for practical applications in the fields of bioremediation and energy production/management [1]. Most of these electrogenic microorganisms can carry out their life cycle forming biofilms on the surface of the electrodes [3,4], where they benefit from favourable physical–chemical (micro)environments and useful trophic relationships These microenvironments are caused by diffusive and/or reactive gradients of different substances, such as electron acceptors or donors that do not exist outside these multi-organism scaffolds [3]. Anodic biofilms are colonised by electrogens, and it is very common that, depending on the source of the inoculum, carbon source, physicochemical parameters, and operational conditions, very complex microbial communities thrive on the surface of bioanodes [4]. The presence of dissolved oxygen (DO) in an anodic medium can determine, to a significant extent, the structure of anodic biofilms, as many microorganisms involved in their functioning are anaerobic or facultative anaerobic [5]

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