Production of sludge-based activated carbon: Optimization and characterization

Activated carbon (AC) was produced from sewage sludge using ZnCl₂, KOH, and H₃PO₄ as the activation agents. Effects of activation temperature (A), impregnation ratio (B), and activation time (C) on the yield and removal efficiency of methylene blue (MB) were investigated. Response surface methodology (RSM) and Box–Behnken design techniques and Design Expert software were used in the experimental design and optimization process. Based on the results, quadratic models for yield and MB removal efficiencies as functions of activation factors (A, B, and C) and their interactions were developed. When ZnCl₂ was used, the statistical analysis results clearly indicated that the yield model was statistically insignificant; however, B, AB, AC, and BC were significant. On the other hand, the MB model, AB, AC, A², A²B, A²C, and AB² were all found to be significant. Characterization of produced AC samples was limited to samples that produced higher values of yield and MB removal efficiency. At optimum conditions, the results showed that surface area and pore size of the produced AC were 319.5 m²/g and 31.28 Å, respectively, which were obtained with ZnCl₂ at activation temperature and time of 700°C and 60 min, respectively, and impregnation ratio of 1:0.6. The Fourier transform infrared spectroscopy results clearly showed that dominant functional groups presented on the surfaces of produced AC samples were O–H, C–C, C–O, and C=O.