Synergistic valorization and efficient adsorption of MB dye via co-hydrothermal carbonization of brewing industry wastes

The waste distiller's grains and yellow water, the two largest types of waste in the brewing industry, were used to prepare activated carbon via co-hydrothermal carbonization. Firstly, three distinct materials were synthesized via phosphoric acid activation: AC-650 (directly activated with H 3 PO 4 ), AC-W-650 (hydrothermally pretreatment with pure water), and AC-Y-650 (hydrothermally pretreatment with yellow water). The specific surface areas of these materials were 13.77, 257.89, and 412.45 m 2 /g, respectively. Notably, Fourier-transform infrared (FTIR) spectroscopy revealed significantly enhanced absorption peaks corresponding to oxygen-containing functional groups on AC-Y-650. The maximum MB adsorption capacities were determined to be 252, 359, and 383 mg/g, respectively. Kinetic and isotherm analyses demonstrated that MB adsorption onto all three adsorbents conformed well to the pseudo-second-order kinetic model and the Langmuir isotherm model. Moreover, increasing the pH and temperature of the MB solution moderately enhanced the adsorption capacity. Furthermore, the co-hydrothermal carbonization strategy was extended to the KOH activation process. Hydrothermal carbonization with yellow water (2376.10 m 2 /g, 731 mg/g) shown marked advantages over pure water (1680.24 m 2 /g, 605 mg/g), and an comparable performance to conventional high-temperature carbonization (2656.85 m 2 /g, 730 mg/g). These findings indicate that activated carbon derived from spent distiller’s grains and yellow water represents an effective, eco-friendly, and cost-efficient adsorbent for MB removal.