Highly efficient removal of amoxicillin from water by three-dimensional electrode system within granular activated carbon as particle electrode

[Display omitted] •Three-dimensional electrode system (3DES) was used for amoxicillin (AMX) removal.•There exists the synergy between adsorption and electrochemical oxidation in 3DES.•Activated carbon in 3DES could be in-situ electrochemically-regenerated.•The mass transfer rate of 3DES is 2.24 times that of the 2DES.•The energy consumption of 3DES is 140.8 kW•h/kg TOC, far below that of 2DES. Amoxicillin (AMX) is a widely used broad-spectrum antibiotic. In this study, a three-dimensional electrode system (3DES) was constructed with granular activated carbon (GAC) packed between the anode and cathode electrodes to degrade AMX. Under optimal conditions of 3DES (current density of 5 mA/cm2, 17 mM NaCl as the electrolyte, an initial pH of 5.56, and a GAC-quartz sand volume ratio of 9:1), the removal efficiency of AMX reached 98.98 % after 2 h of treatment. It was also shown that the total organic carbon (TOC) removal efficiency (R) and reaction rate constant (k) of 3DES were 47.6 % and 0.22 h−1, respectively, much higher than the sum of the two-dimensional electrode system (2DES) and adsorption process (30.7 % and 0.12 h−1). Thus, there existed the synergy between electrolysis and adsorption in 3DES, which enhanced the TOC removal efficiency and removal rate by up to 35.5 % and 46.8 %, respectively. Electrochemical characterization was explored using an electrochemical workstation. It demonstrated that GAC played an important role in reducing the mass transfer resistance, and the mass transfer rate of 3DES was 2.24 times that of the 2DES. It was also deduced that AMX adsorbed on the surface of GAC directly participated in the electrochemical oxidation to achieve the in-situ regeneration of activated carbon. The results of Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) of GAC verified it again. In summary, 3DES has good electrochemical performance, and it is an efficient, cost-effective, and environmentally friendly system for AMX degradation.