Performance of vermicompost derived hydrochars for methylene blue removal via ultrasound assisted adsorption

This study investigated the ultrasound-assisted adsorption of methylene blue (MB) onto vermicompost (VC) derived hydrochars prepared at different hydrothermal treatment temperatures (220, 250, and 280 °C). The effects of pH, time, and initial concentration on the adsorption process were evaluated. The kinetic and isotherm models were applied to fit the experimental data. The results showed that the VC hydrochars exhibited superior adsorption capacity for MB under alkaline conditions. The adsorption process was influenced by chemical interactions between the MB molecules and the surface of hydrochars, and the adsorption process was irreversible chemisorption. VC220 hydrochar demonstrated the highest adsorption capacity for MB, followed by VC250 and VC280 hydrochars. The Pseudo Second Order kinetic model and Langmuir isotherm model provided the best fits to the experimental data. This suggests that the adsorption of MB onto VC hydrochars follows a second-order reaction mechanism and monolayer adsorption process with high adsorption capacities.