Elsevier

Biofilm

Volume 4, December 2022, 100064
Biofilm

The effect of intermittent anode potential regimes on the morphology and extracellular matrix composition of electro-active bacteria

https://doi.org/10.1016/j.bioflm.2021.100064Get rights and content
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Highlights

  • Continuous acetate feeding and intermittent anode potential lead to EPS production in electro-active bacteria.

  • A charge balance was made including soluble EPS and planktonic cells.

  • Patchy biofilm morphologies and more planktonic cells were observed when intermittent anode potential was applied.

  • Biofilms grown under intermittent anode potential had more EPS and more proteins.

Abstract

Electro-active bacteria (EAB) can form biofilms on an anode (so-called bioanodes), and use the electrode as electron acceptor for oxidation of organics in wastewater. So far, bioanodes have mainly been investigated under a continuous anode potential, but intermittent anode potential has resulted in higher currents and different biofilm morphologies. However, little is known about how intermittent potential influences the electron balance in the anode compartment. In this study, we investigated electron balances of bioanodes at intermittent anode potential regimes. We used a transparent non-capacitive electrode that also allowed for in-situ quantification of the EAB using optical coherence tomography (OCT). We observed comparable current densities between continuous and intermittent bioanodes, and stored charge was similar for all the applied intermittent times (5 mC). Electron balances were further investigated by quantifying Extracellular Polymeric Substances (EPS), by analyzing the elemental composition of biomass, and by quantifying biofilm and planktonic cells. For all tested conditions, a charge balance of the anode compartment showed that more electrons were diverted to planktonic cells than biofilm. Besides, 27–43% of the total charge was detected as soluble EPS in intermittent bioanodes, whereas only 15% was found as soluble EPS in continuous bioanodes. The amount of proteins in the EPS of biofilms was higher for intermittent operated bioanodes (0.21 mg COD proteins mg COD biofilm−1) than for continuous operated bioanodes (0.05 mg COD proteins mg COD biofilm−1). OCT revealed patchy morphologies for biofilms under intermittent anode potential. Overall, this study helped understanding that the use of a non-capacitive electrode and intermittent anode potential deviated electrons to other processes other than electric current at the electrode by identifying electron sinks in the anolyte and quantifying the accumulation of electrons in the form of EPS.

Keywords

Bioanode
Intermittent anode potential
Electron storage
EPS formation

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