Biological catalyzed denitrification by a functional electropolymerization biocarrier modified by redox mediator

► A new denitrification process with functional biocarriers was developed. ► The denitrification rate was increased 1.5-fold by functional biocarriers. ► The accelerating mechanism of AQS was explained from ORP and electron transport. Electropolymerization biocarriers were prepared by the electropolymerization of polypyrrole (PPy) on an active carbon felt (ACF) electrode using doping anions anthraquinone-2-sulfonate (AQS) or Na2SO4. The functional electropolymerization biocarrier (ACF/PPy/AQS) with AQS was used as an immobilized redox mediator for the denitrification process. The characteristics of the electropolymerization biocarriers were analyzed by scanning electron microscope, elemental analyses, Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The results suggested that the denitrification efficiency increased nearly 1.5-fold with ACF/PPy/AQS (0.04mmolL−1 AQS) compared to the control. A linear correlation was found for the k value and the AQS concentration (CAQS), which was k=624.71CAQS+83.87 (R2=0.9893). The ORP value stabilized around −200mV for the denitrification process with ACF/PPy/AQS, which was −25mV lower than that with ACF/PPy/Na2SO4. Repeated-batch operations indicated that the denitrification efficiency with ACF/PPy/AQS maintained over 90% of the original value and exhibited better catalytic activity and durability.