A biocompatible electrode/exoelectrogens interface augments bidirectional electron transfer and bioelectrochemical reactions.

Bidirectional electron transfer is about that exoelectrogens produce bioelectricity via extracellular electron transfer at anode and drive cytoplasmic biochemical reactions via extracellular electron uptake at cathode. The key factor to determine above bioelectrochemical performances is the electron transfer efficiency under biocompatible abiotic/biotic interface. Here, a graphene/polyaniline (GO/PANI) nanocomposite electrode specially interfacing exoelectrogens (Shewanella loihica) and augmenting bidirectional electron transfer was conducted by in-situ electrochemical modification on carbon paper (CP). Impressively, the GO/PANI@CP electrode tremendously improved the performance of exoelectrogens at anode for wastewater treatment and bioelectricity generation (about 54 folds increase of power density compared to blank CP electrode). The bacteria on electrode surface not only showed fast electron release but also exhibited high electricity density of extracellular electron uptake through the proposed direct electron transfer pathway. Thus, the cathode applications of microbial electrosynthesis and bio-denitrification were developed via GO/PANI@CP electrode, which assisted the close contact between microbial outer-membrane cytochromes and nanocomposite electrode for efficient nitrate removal (0.333 mM/h). Overall, nanocomposite modified electrode with biocompatible interfaces has great potential to enhance bioelectrochemical reactions with exoelectrogens.

Interpretation of adhesion behaviors between bacteria and modified basalt fiber by surface thermodynamics and extended DLVO theory.

Surface properties of carrier are critical for microorganism initial adhesion and biofilm formation in wastewater treatment. Until now, there are few reports on adhesion behaviors between bacteria and inorganic fiber surface. In this study, inorganic basalt fiber (BF) was modified with cationic polyacrylamide (CPAM) to make surface more hydrophilic and positively charged. The initial adhesion behaviors of BF modified with CPAM (CMBF) were interpreted by thermodynamics and extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. According to the total interaction energy calculated by the extended DLVO theory, insurmountable energy barrier between BF and Escherichia coli (E. coli) made irreversible adhesion unachievable due to hydrophobicity and electronegativity of BF, but allowed reversible adhesion at second minimum. By contrast, the energy barrier between CMBF and E. coli could be overcome allowing irreversible bacterial adhesion and thus a huge amount of biomass because of hydrophilicity and electropositivity of CMBF. The results showed the total interaction energies were dominated by Lewis acid-base and electrostatic interactions and coating BF with CPAM could promote initial bacterial adhesion on carrier surface. Overall, the extended DLVO theory provides a comprehensive tool to interpret initial adhesion behaviors between bacteria and inorganic fibers.