One-step microwave conversion of paper mill sludge into magnetic activated carbon for the removal of pharmaceuticals from water

This study introduces an innovative approach to convert primary sludge (PS) from the paper mill industry into magnetic activated carbon (MAC). As alternative to multi-step strategies, a one-step microwave pyrolysis process was studied, combining activation and magnetization in a single stage. The main goal was to identify the synthesis parameters that significantly affect the production of magnetically recoverable MAC, and to test its applicability for the removal of pharmaceuticals from wastewater effluents, namely carbamazepine (CBZ), sulfamethoxazole (SMX), and ibuprofen (IBU). A fractional factorial design was employed to assess the influence of four process production variables (FeCl3:PS ratio, KOH:PS ratio, pyrolysis temperature, and post-pyrolysis wash) on six responses (production yield, specific surface area (SBET), saturation of magnetization (MS) and percentage of adsorption for CBZ, SMX and IBU. Statistical analysis revealed that MAC produced with a FeCl3:PS ratio of 1:2, a KOH:PS ratio of 1:5, pyrolysis at 800 degrees C, and acid washing with 1 M HCl resulted in satisfactory SBET values (338 m2 g- 1), sufficient MS (22 emu g- 1) for easy recovery from water and high pharmaceuticals adsorption. Adsorption kinetics for the selected MAC were rapid, reaching equilibrium within 1 h for all pharmaceutical systems. The Langmuir model described equilibrium isotherms, showing maximum adsorption capacities (qm) in ultrapure water of 217 f 6, 261 f 6, and 210 f 6 mu mol g- 1 for CBZ, SMX, and IBU, respectively, while in wastewater effluent, qm were 162 f 3, 87 f 4, and 103 f 5 mu mol g- 1, respectively.