Enhanced fluoroglucocorticoid removal from groundwater in a bio-electrochemical system with polyaniline-loaded activated carbon three-dimensional electrodes: Performance and mechanisms

Abstract

This study aimed to investigate the removal performance and mechanisms of dexamethasone (DEX), a representative fluoroglucocorticoid (FGC), from micro-polluted oligotrophic groundwater in a bio-electrochemical system amended with polyaniline-loaded activated carbon (PANI@AC) as three-dimensional particle electrodes (BES-3D). The BES-3D achieved a DEX removal efficiency of 95.7%, which was 39.0% and 14.1% higher than that of a single biological system (SBIO) and two-dimensional bio-electrochemical system (BES-2D), respectively. The preliminary metabolic mechanism of defluorination accounted for 53.5%, 41.1%, and 16.3% in BES-3D, BES-2D, and SBIO, respectively, which was accompanied by demethylation, side-chain fracture, and hydroxyl oxidation for ketone formation and final-ring opening. The main mechanism by which removal was improved in BES-3D was the enrichment of functional microbes and enhancement of the expression of dehalogenation genes. The relative abundance of functional microbes with electron transfer ability and reductive dehalogenating genera, i.e., Pseudomonas, Methylotenera, Desulfuromonas, Sphingomonas, and Microbacterium, in BES-3D was 3.7–6.1 times higher and the copy number of functional genes was 1.9 times higher than those of SBIO, which contributed to the high DEX removal.