Polypyrrole materials enhanced extracellular electron transfer and nitrobenzene reduction by Geobacter sulfurreducens

Extracellular respiratory bacteria (ERB) have been confirmed to promote nitrobenzene (NB) reduction through extracellular electron transfer (EET) process. However, the efficiency of EET process via artificially regulating cytochrome or nanowires were limited depending on the types and metabolic function of ERB. This work investigated the effects of conductive polypyrrole (Pyy) materials (0.05-0.50 g/L) as electron shuttle (ES) on G. sulfurreducens PCA (as typical ERB) and associated NB reduction process. The results showed that the Pyy-PCA composite system with the dosing of 0.50 g/L Pyy materials achieved complete reduction of 100 mu M NB to aniline within 12 h, whose first-order reduction rate was as 62.5 times higher than that of pure PCA cells. The control treatment of Pyy materials was capable to remove 32 mu M NB within 2 h through physical adsorption rather than reduction process. The morphology and structural characterization of Pyy materials with PCA strain confirmed the formation of Pyy-PCA composite system which maintained stable structures during the NB reduction. Electrochemical measurements suggested that the Pyy-PCA composite system had better electrochemical properties than both pure PCA cells and original Pyy materials under the experimental condition, which might play a vital role in accelerating electron transfer for NB reduction. This work enriched the understanding of the interaction between Pyy materials and ERB, and provided a feasible way for the bioremediation of nitroaromaticcontaining environment.