Application of polypyrrole modified cathode in bio-electro-Fenton coupled with microbial desalination cell (MDC) for enhanced degradation of methylene blue

Abstract

To enhance the selectivity of 2 e−1 oxygen reduction reaction, polyacrylonitrile-based carbon fiber brush, after being coated with pyrrole via chronoamperometry, is employed as cathode for H2O2 electrogeneration through bio-electro-Fenton process. Besides, a recirculated microbial desalination cell is assembled to transfer anolyte from anode to cathode chamber, to avoid pH imbalances. It is found that H2O2 productivity for recirculated microbial desalination cell groups with ploypyrrole modified cathode reached 24.07 g H2O2 m−3 d−1, while which is only 6.95 g H2O2 m−3 d−1 for microbial desalination cell group without recirculation. At the inner recirculating rate of 900 μL min−1, the maximal power density of recirculated microbial desalination cell group reaches 566 mW m−3, while which of the microbial desalination cell group without recirculation reaches only 267 mW m−3. Moreover, the average Faradic efficiency and desalting efficiency of the recirculated microbial desalination cell with ploypyrrole modified cathode reach 28.79% and 64.98%, comparing to those of the microbial desalination cell groups without recirculation reach only 5.20% and 44.55%. According to the component identification using mass spectrum, two degradation pathways of methylene blue via bio-electro-Fenton using ploypyrrole modified cathode are proposed, and the generated smaller molecules would be appropriate for further in-depth treatment.