Enhanced removal of tetracycline using three-dimensional electrochemical system with Fe/N/S co-doped coffee grounds biochar particle electrodes: Performance and mechanism

In this study, Fe/N/S co-doped biochar was prepared from coffee grounds for using as particle electrodes (PE) to construct a three-dimensional electrochemical system (3DES). Tetracycline (TC) was selected as the simulated contaminant to evaluate the performance of 3DES in removing trace organic contaminates form water. First, characteristics analysis revealed that the PE was the micron-level carbon-based solid material with good electric conductivity, excellent catalytic performance and stability. Then, the performance of the 3DES was evaluated. About 92 % of TC and 76 % of total organic carbon (TOC) was removed under optimal operation conditions of potassium peroxydisulfate (PDS) addition of 3 mM, current density of 100 mA·cm⁻², PE dosage of 0.5 g·L⁻¹ and solution initial pH of 7. The 3DES exhibited satisfactory stability and application prospect for trace organic contaminates treatment in real water. Furthermore, analysis of the reactive oxidized species (ROS) revealed that the ¹O₂ and O₂^•− contributed much more to the TC removal than ^•OH and SO₄^•−. In addition, three possible pathways of TC removal in 3EDS was proposed. TC was degraded to organics with simple structures through functional group removal, ring-opening, and CO bond rupturing, and finally mineralized into CO₂, H₂O, and NO₃^-, etc. Finally, toxicity evaluation of the intermediate products indicated that the ecological risks of TC was effectively reduced through 3DES. This study provided a new strategy for resource utilization of carbon-based solid waste and efficient treatment of refractory wastewater.