investigations can progress. The synthetic seawater used here
corresponded to the standard composition implemented in
physical-chemistry studies to characterize the abiotic corrosion of
materials in seawater. Consequently, it did not contain the micronutrients, vitamins and other possible traces of organic compounds
that are present in natural seawater. The current densities obtained
here in the “physicochemical” synthetic seawater show the interest
of going ahead with the design of a “biological” synthetic seawater,
which would be able to sustain full electro-activity of the seawater
electroactive microbial strains. Further studies will aim at defining
what micro-components, present in natural seawater, should be
added into the composition of the “physicochemical” synthetic
seawater to improve the biocathode performance in a synthetic
medium.
The biocathodes were checked by cyclic voltammetry at
different times during the chronoamperometries. All the monospecies biocathodes gave similar shapes of the current-potential
curves, only the values of the current density were different. The
best performance was around 0.8 A m2 at 0.6 V/SCE with the
Pseudoalteromonas strain (Fig. 2). The open circuit potential was
around 0.1 V/SCE for most monospecies biocathodes and the
biocatalytic effect started in the range from 0.1 V/SCE to 0.3 V/
SCE, as illustrated in Fig. 2 with two extreme examples. When the
solution was stirred, the current-potential curve had an exponential form, characteristic of electron-transfer limited kinetics. Gentle
stirring was consequently sufficient to suppress mass transfer
limitation, showing that the electron transfer kinetics was not very
efficient. As expected, bubbling air into the reactor shifted the curve
to higher currents than stirring, because it ensured the solution was
stirred and also increased the concentration of dissolved oxygen in
the bulk.
Monospecies vs. multispecies biofilms
The performance of multispecies biocathodes that form spontaneously in seawater under identical operating conditions