Halotolerant bioanodes: The applied potential modulates the electrochemical characteristics, the biofilm structure and the ratio of the two dominant genera

Abstract

The development of economically-efficient microbial electrochemical technologies remains hindered by the low ionic conductivity of the culture media used as the electrolyte. To overcome this drawback, halotolerant bioanodes were designed with salt marsh sediment used as the inoculum in electrolytes containing NaCl at 30 or 45g/L (ionic conductivity 7.0 or 10.4S·m(-1)). The bioanodes were formed at four different potentials -0.4, -0.2, 0.0 and 0.2V/SCE to identify the effect on the electrochemical kinetic parameters, the biofilm structures and the composition of the microbial communities. The bioanodes formed at -0.4V/SCE were largely dominated by Marinobacter spp. Voltammetry showed that they provided higher currents than the other bioanodes in the range of low potentials, but the maximum currents were limited by the poor surface colonization. The bioanodes formed at -0.2, 0.0 and 0.2V/SCE showed similar ratios of Marinobacter and Desulfuromonas spp. and higher values of the maximum current density. The combined analysis of kinetic parameters, biofilm structure and biofilm composition showed that Marinobacter spp., which ensured a higher electron transfer rate, were promising species for the design of halotolerant bioanodes. The challenge is now to overcome its limited surface colonization in the absence of Desulfuromonas spp.

Effect of pore size on the current produced by 3-dimensional porous microbial anodes: A critical review

“…Internal microbial colonization was also observed in fibre porous electrodes. A continuous, thin biofilm has been observed on the fibres of graphite felt with a thickness approaching 10 µm after 12 days of polarization in hypersaline environment (Rousseau et al, 2016). Nevertheless, as discussed above for monolithic porous electrodes, the penetration depth could be restricted.…”

Understanding the cumulative effects of salinity, temperature and inoculation size for the design of optimal halothermotolerant bioanodes from hypersaline sediments

“…Parameters corresponding to the central point (0,0,0) are repeated four times to establish that the experimental data is within the normal dispersion and that repeatability is ensured, and also to estimate the pure error variance. Selected boundaries of the variables for the BBD (Table 1) were based on preliminary experimental tests performed on HCSE as well as results of previous studies [3,19,20].…”

“…The integration of microbial catalysis with electrochemistry has given rise to several innovative processes, broadly known as bioelectrochemical systems (BES), with potential energy, environmental and industrial applications such as electricity generation, hydrogen production, wastewater treatment, pollutant removal and biomolecule synthesis [1,2,3,4,5]. In BES, the efficiency of bioanodes, in terms of electron exchange kinetics, ability to recover electrons from soluble molecules and, finally, robustness, is the key to considering their industrial exploitation [2,6].The apparent rates of electron transfer of bioanodes have greatly improved and, today, it has become possible to obtain very high current densities (greater than several tens of A/m 2 ) by using anodes of different materials, with different geometrical designs, and with chemical, thermal or electrochemical surface treatments or coatings [6,7,8].…”

“…However, all these studies were carried out at temperatures lower than or equal to 37°C and so none of this work examined the combined effect of increased salinity and high temperature on the bioanode current production, yet the salinity and thermal tolerance of halothermophilic microorganisms would make it possible to consider the design of halothermotolerant bioanodes that would be truly suitable for the treatment of hot, highly saline wastewater. In addition, the approaches used to improve the performance of bioanodes under saline or thermal conditions have so far been carried out by monitoring the influence of a single factor at a time, by following a single experimental response, which is often only the generation of current [3,6,7,8,15,21,22].These approaches, known as one-variable-at-a-time optimization, do not include the interactive effects between the variables studied. Consequently, this optimization does not depict the effects of all the factors on the response.…”

The Effect of Intermittent Limiting Anodic Current Stimulation on the Electro Activity of Anodic Biofilms

“…To activate MFC systems, the most commonly employed method is to, after inoculation with a bacterial source, connect a constant external resistance between the anode and the cathode, thus encouraging growth of electro active microorganisms. Alternatively, some studies employed a poised constant anode potential for the growth of electro active microorganisms [17][18][19][20], in order to activate the microbial anode and then to explore the effect of electrode potential on the development of electro active biofilms. In circuits with an external resistance or with poised anode potential, biofilm formation is the processes in which electro-active microorganisms (probably also involving non-electro active strains in systems with mixed cultures) grow adaptively in response to either time-dependent anode potentials (e.g., in constant external resistance operations) or to constant anode potentials (e.g., in poised anode potential operations).…”