Magnetite-enabled self-assembled microbial networks for centimeter-scale electron transfer in a soil bioelectrochemical system

Abstract

• MNPs enhanced electrogenic acetate oxidation in sand packed BES up to 2.2-fold • Current generation increased up to 2.6 fold in presence of MNPs • MNPs enabled formation of conductive network composed of electroactive bacteria • The conductive network spanned over 1.8 cm away from the anodic surface • Higher abundance of electroactive microorganisms in the packing material with MNPs Electroactive biofilms (EABs) play a pivotal role in bioelectrochemical systems (BESs), enabling microbial respiration on solid electrodes. However, the spatial limitations of electron transfer often constrain biofilm development and performance, particularly in porous, heterogeneous environments. In this study, we investigated the effect of magnetite nanoparticles on the formation and electrochemical behavior of EABs in continuous-flow reactors packed with sand or a sand–magnetite mixture. Chronoamperometry revealed that the magnetite-amended reactor produced significantly higher electric currents (up to 2.6-fold) alongside increased acetate removal rates (up to 2.2-fold) and prolonged electron discharge following substrate depletion, indicative of enhanced electron storage and release. Cyclic voltammetry confirmed greater bioelectrocatalytic activity and revealed an over fourfold increase in anode capacitance, suggesting the development of a more extensive and electrochemically active biofilm. Spatial profiling with a titanium probe demonstrated that electrocatalytic activity extended up to 1.8 centimeters from the anode only in the presence of magnetite, consistent with the formation of a biologically mediated conductive network beyond the electrode surface. In line with these evidences, a higher abundance of electroactive microorganisms was detected within the packing material surrounding the anode. These findings provide the first experimental support for the concept of Diffuse Electro-Conductive Zones (DECZs) and suggest a viable strategy to extend the radius of electrode influence in soil BESs. This approach may enhance the effectiveness of in situ bioremediation technologies by enabling mesoscale redox connectivity in complex subsurface environments.

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Identifiers

DOI

10.1016/j.ceja.2025.100945

Journal

Chemical Engineering Journal Advances

Year

2025