Fabrication of sewage sludge biochar with different pyrolysis temperatures for adsorption treatment of wastewater

Sewage sludge, a major byproduct of municipal wastewater treatment, presents both environmental challenges and resource utilization opportunities. In this study, biochars were prepared from sewage sludge at pyrolysis temperatures ranging from 400°C to 800°C and evaluated for their adsorption performance in removing dissolved organic carbon (DOC), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) from secondary effluent. The physicochemical properties of the biochars were characterized using Brunauer–Emmett–Teller (BET) surface area analysis, Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FE-SEM), and elemental analysis. The results showed that higher pyrolysis temperatures significantly increased surface area and pore development. Although surface functional groups decreased with increasing pyrolysis temperature, the adsorption capacities improved overall. The biochar produced at 800°C (BC800) exhibited the highest removal efficiency for organic contaminants, while the biochar produced at 500°C (BC500) showed the best performance for phosphorus removal. To assess energy efficiency, the energy-normalized adsorption capacity (ENAC) was introduced. Although the biochar produced at 700°C (BC700) exhibited the highest ENAC values for COD and TN, the choice of an appropriate pyrolysis temperature that balances removal efficiency and energy performance is crucial. These findings highlight the importance of pyrolysis temperature in tailoring both the adsorption and energy performance of sewage sludge biochar. This study provides theoretical and practical insights into the use of thermally optimized biochar for sustainable wastewater treatment applications.