ABSTRACT
The climate crisis requires rethinking wastewater treatment to recover resources, such as nutrients and energy. In this scenario, purple phototrophic bacteria (PPB), the most versatile microorganisms on earth, are a promising alternative to transform the wastewater treatment plant concept into a biorefinery model by producing valuable protein-enriched biomass. PPB are capable of interacting with electrodes, exchanging electrons with electrically conductive materials. In this work, we have explored for mobile-bed (either stirred or fluidized) cathodes to maximize biomass production. For this purpose, stirred-electrode reactors were operated with low-reduced (3.5 e-/C) and high-reduced (5.9 e-/C) wastewater under cathodic polarization (-0.4 V and -0.8 V vs. Ag/AgCl). We observed that cathodic polarization and IR irradiation can play a key role in microbial and phenotypic selection, promoting (at -0.4 V) or minimizing (at -0.8 V) the presence of PPB. Then, we further study how cathodic polarization modulates PPB biomass production providing a fluid-like electrode as part of a so-called photo microbial electrochemical fluidized-bed reactor (photoME-FBR). Our results revealed the impact of reduction status of carbon source in wastewater to select the PPB photoheterotrophic community and how electrodes drive microbial population shifts depending on the reduction status of such carbon source.
ABSTRACT
The capacity of electroactive bacteria to exchange electrons with electroconductive materials has been explored during the last two decades as part of a new field called electromicrobiology. Such microbial metabolism has been validated to enhance the bioremediation of wastewater pollutants. In contrast with standard materials like rods, plates, or felts made of graphite, we have explored the use of an alternative strategy using a fluid-like electrode as part of a microbial electrochemical fluidized bed reactor (ME-FBR). After verifying the low adsorption capacity of the pharmaceutical pollutants on the fluid-bed electrode [7.92 ± 0.05% carbamazepine (CBZ) and 9.42 ± 0.09% sulfamethoxazole (SMX)], our system showed a remarkable capacity to outperform classical solutions for removing pollutants (more than 80%) from the pharmaceutical industry like CBZ and SMX. Moreover, the ME-FBR performance revealed the impact of selecting an anode potential by efficiently removing both pollutants at + 200 mV. The high TOC removal efficiency also demonstrated that electrostimulation of electroactive bacteria in ME-FBR could overcome the expected microbial inhibition due to the presence of CBZ and SMX. Cyclic voltammograms revealed the successful electron transfer between microbial biofilm and the fluid-like electrode bed throughout the polarization tests. Finally, Vibrio fischeri-based ecotoxicity showed a 70% reduction after treating wastewater with a fluid-like anode (+ 400 mV), revealing the promising performance of this bioelectrochemical approach.
