In-situ fabrication of a three-dimensional nanopalladium network into a biocathode enhances chloramphenicol degradation

Bioelectrochemical systems (BESs) with biocathodes are a promising technology for antibiotic removal, but they are often limited by inefficient electron transfer from the cathode to bacteria due to the low conductivity of biofilms. In this study, a conductive cathodic biofilm was established through in-situ synthesis and immobilization of biogenic palladium nanoparticles (Pd-NPs) for chloramphenicol (CAP) removal. Compared to the control biocathode, the limiting current density of the Pd-fabricated biocathode (Pd-biocathode) was increased by 4.3 times, and the charge transfer resistance was decreased by 673 % due to enhanced extracellular electron transfer. The Pd-biocathode showed accelerated CAP removal, with the removal rate constant (k) increasing by 44 % compared to the control biocathode. In particular, the removal efficiency of the Pd-biocathode increased by 71 % within 4 h. These results might be explained by the decreased charge transfer resistance of the biocathode, the selective enrichment of functional bacteria and the up-expression of genes encoding organic substance metabolism and degrading enzyme activity. In addition, the increased applied voltage negligibly affected the enhancement of CAP removal in the Pd-biocathode BES, but it enhanced CAP removal in the control BES. Additionally, glucose addition markedly improved the CAP removal rates. This work demonstrates the potential of an effective and simple biocathode modification strategy through the in-situ synthesis of conductive NPs that could increase the antibiotic removal rates, but also provides new insight into how microbe-electrode interactions can be improved to enhance BES performance in wastewater treatment.