Adsorption and in-situ electrochemical regeneration in a clay-packed continuous reactor for the removal of the antibiotic sulfamethoxazole

This study aims to investigate a reactor that allows the continuous adsorption of the antibiotic contaminant using clay as adsorbent and the in-situ electrochemical regeneration of the saturated absorbent. It is noteworthy that the electrochemical regeneration of adsorbents has not been widely investigated and studies that explore alternative adsorbents are rare. SpC clay and the antibiotic sulfamethoxazole were selected, through preliminary adsorption tests, to be investigated in this study. Density functional theory (DFT) calculations were conducted to understand the particularities of antibiotic adsorption. In the continuous system adsorption tests, the flow rate of 0.3 mL min-1 was selected to proceed with the electrochemical regeneration experiments. The influence of operating parameters on regeneration, such as anode type, electrolyte type and concentration, current density and time, was examined. Clay stability was investigated for five successive cycles, under operating conditions of 62.5 mA cm-2, DSA anode, 0.2 mol L-1 NaCl, and 15 min of electrolysis. The characterization analyses indicated that the electrochemical regeneration did not deteriorate the chemical surface of the clay. Electrolysis promoted the creation of new active sites in the clay after the first cycle, obtaining regeneration efficiency greater than 100 %. The reactor investigated here offered a promising approach for efficient removal of the emerging contami-nant, since the process can be operated in-situ, with low energy consumption (0.42 kWh kg-1) over a short time-span (15 min).