Efficient Adsorption of Methylene Blue in Water by Torrefaction Biochar from Agro-Industrial Residue: Thermochemical Characterization and Kinetic Studies

This research investigates the adsorption potential of four types of absorbents produced from agro-industrial waste (grape pomace - GP, tree pruning - TP, sugarcane bagasse - SB and eucalyptus sawdust - ES) for the uptake of Methylene Blue (MB) dye from aqueous solution. A kinetic model based on a hybrid-order rate equation was fitted to experimental data. The result showed that from the biochars obtained in dry torrefaction at 300 ºC - 60 min, BGP-300 presented the highest mass yield (58.84%) and energy yield (69.56%), followed by the BTP-300 > BES-300 > BSB-300. Adsorption studies showed that BGP-300 had a better performance in the uptake of MB, with removal efficiency (R_e) of 96.5% and adsorption capacity at equilibrium (q_e) of 9.3 mg g-1, followed by tree pruning biochar (BTP-300), R_eof 65.0% and q_eof 5.3 mg g-1. Whereas eucalyptus sawdust (BES-300) and sugarcane bagasse (BSB-300) biochar did not provide significant removal of MB. Adsorption kinetic is best described by second order rate with R² varying from 0.75 to 0.96. Desorption studies show a low concentration released to the solution, indicating that adsorption may occur physically. Therefore, this research provides comprehensive insights into the adsorption characteristics of different biochar, emphasizing the potential of BGP-300 and BTP-300 as effective for MB uptake from aqueous solution.