Ano-Cathodophilic Biofilm Catalyzes Both Anodic Carbon Oxidation and Cathodic Denitrification

Biocathodic denitrification using bioelectrochemical systems (BES) have shown promise for both wastewater and groundwater treatment. Typically, these systems involve anodic carbon oxidation and cathodic denitrification catalyzed by two electroactive biofilms located separately at an anode and a cathode. However, process efficiencies are often limited by pH drifts in the respective electrode-biofilms: acidification (pH <5.5) in the bioanode and basification (pH >8.5) in the biocathode. Here, we describe for the first time a single electroactive biofilm that acts as a bioanode and a biocathode, alternately catalyzing anodic acetate oxidation (Coulombic efficiency (CE) 85.3%) and cathodic denitrification (CE 87.3%) (-400 mV Ag/AgCl). Our results indicate that the ano-cathodophilic biofilm denitrified autotrophically using the electrode (-200 to -600 mV Ag/AgCl) as a direct electron donor. Further, the alkalinity produced from cathodic denitrification partially (19%) neutralized the acidity of the anodic reaction. Switching the electrode potential to temporarily favor either an anodic or cathodic reaction may represent a unique method for removing carbon and nitrate from contaminated liquors. This study offers new insights into the development of sustainable BES-based nutrient removal processes.