A Novel Biochar from Agro-Industrial Waste: Synthesis, Characterization, and Application for Acetylsalicylic Acid...

Due to drugs not being completely metabolized and excreted in their original form or as byproducts that contaminate water resources, the conventional treatment process often fails to remove these pollutants. Consequently, some studies seek to use waste to create materials capable of purifying water. Adsorption, being a process of low complexity and operational cost, stands out as a widely used process for wastewater treatment. In this context, the present work aims to synthesize and characterize a novel biochar from Lagenaria siceraria for the removal of the acetylsalicylic acid (ASA) drug by the adsorption process (kinetic, equilibrium, and thermodynamic) and to evaluate its ecotoxicity in Artemia salina. The biochar showed a heterogeneous, porous, and negatively charged surface (-18.76 ± 8.05 mV), with a surface area of 0.35 m² g^-1 and pH_ZCP = 6.95. It achieved 42% ASA removal under ideal conditions (10 mg L^-1 ASA, 0.25 g L^-1 biochar, and pH 4) and exhibited a maximum capacity (q _max) of 137.33 mg g^-1. In the thermodynamic study, there was a greater removal rate of 77% at 35 °C, and the best model was the Khan model in adsorption equilibrium (R ² = 0.999), which indicates mono- and multilayer adsorption by electrostatic action. At low ASA concentrations, the pseudo-first-order (PFO) model presented the best fit, indicating a predominance of fast adsorption at surface sites and physical interactions. Meanwhile, for higher concentrations of ASA, the pseudo-second-order (PSO) model was more adequate, suggesting an increasing contribution of specific chemical interactions at higher-energy sites. The biosorbent showed no ecotoxicity between 100-1000 mg L^-1 and a lethal dose of 100% ASA (L_D100) at 300 mg L^-1. Therefore, biochar can be used as an alternative material for the removal of organic pollutants, such as drug residues.