Removal of Tetracycline from Water Using Activated Carbon Derived from the Mixture of Phragmites australis and Waterworks Sludge

Sludge-based activated carbon with doped Phragmites australis was prepared using an environment-friendly method to treat waterworks sludge (WS) and obtain an economical adsorbing material for tetracycline (TC) elimination. For the WS, P. australis was used as an additive to optimize the preparation of activated carbon. Optimum preparation conditions were as follows: activation temperature, 600 °C; ZnCl₂ concentration, 3 mol/L; activation time, 50 min; impregnation ratio (weight of mix sample: weight of ZnCl₂) of 1:2.5; and the mixed ratio of P. australis with WS, 40%. The obtained activated carbon owned well-developed Brunauer–Emmett–Teller surface area (949.90 m²/g). The acidic and basic functional groups were improved to 0.762 and 0.016 mmol/g, respectively. The pseudo-second-order kinetic and Freundlich isotherm equations were more suitable models to simulate adsorption with the maximum adsorption capacity of 153.4 mg/g. According to the thermodynamic parameters, the adsorption process was spontaneous and endothermic. Electrostatic interaction, hydrogen bonding formation, and ion complexation adsorption mechanisms were the mechanisms underlying the adsorption of TC.