Ferromagnetically modified N self-doped tea residue biochar three-dimensional electrode for the treatment of tetracycline in high salt water environment

Tetracycline hydrochloride (TCH) has become one of the representative organic pollutants in marine wastewater. The high-salt water environment characteristics of marine wastewater increase the difficulty of TCH repair. Three-dimensional electrode technology can utilize chloride ions in the marine wastewater as an electrolyte to improve the degradation of the reaction system. In this study, a ferromagnetic modified N self-doped tea residue biochar (FNTB) was prepared by using the N-rich property of tea residue waste. A three-dimensional electrode system (3D-FNTB) for efficient treatment of TCH in high-salinity mariculture wastewater was established by using FNTB as particle electrode. The chloride ions in the water were converted into active chlorine to assist in the removal of TCH. The presence of N and Fe in FNTB could effectively improve its conductivity and electrocatalytic activity, so that FNTB could simultaneously act as an electrode material, Fenton/Fenton-like catalyst and adsorbent during the removal of TCH, and simultaneously remove TCH efficiently. Under the conditions of initial NaCl concentration of 20 g L⁻¹, pH of 3.8, and voltage of 2 V, the removal rate of TCH at 100 mg L⁻¹ by 2 g FNTB reached 99.97 %, and the removal rate of TOC was 78.86 %. The removal rate of TCH by FNTB could still reach 98.54 % after repeated use for 10 times. This study provided an idea for the treatment of high-salt organic wastewater and resource utilization of tea residue.