Preparation of low-cost sludge-based highly porous biochar for efficient removal of refractory pollutants from agrochemical and pharmaceutical wastewater.

Producing a high-performance sludge biochar through a feasible method is a great challenge and is crucial for practicability. Herein, we reported a highly porous sludge biochar synthesized from agrochemical-pharmaceutical and municipal sludge blends through a novel pyrolysis-acid treatment-post pyrolysis method. The optimized biochar named ASMS91 obtained interconnected pores with a total pore volume of 0.894 cm³/g and a surface area of 691.4 m²/g through extended acid wash and subsequent post-pyrolysis, which is superior to non-activated sludge biochar. ASMS91 removed 45.3 % of wastewater COD (156 mg/L) in 24 h, which was rapid and higher performance than commercial activated carbon (1000 iodine number). This outstanding performance is due to its high adsorption ability of long-chain aliphatic compounds (e.g., 2,4-Di-tert-butylphenol, neophytadiene and eicosane) into mesopores, which accounts for 71.8 % of pore filling. ASMS91 was highly recyclable, and adsorption was reduced by only 5.3 % after the 4th cycle. It also outperformed other sludge biochar in literature in removing perfluorooctanoic acid (PFOA), 6:2 fluorotelomer sulfonate (6:2 FTS), sulfamethoxazole, methylene blue, and methylene orange. Finally, the feasibility of our proposed method was validated by a brief techno-economic analysis. This feasible approach may support future research regarding sludge valorization and low-cost chemical wastewater treatment.