Steam activated hydrochar from wine waste for the removal of pharmaceutical micropollutants from water

This study explores the potential of hydrochar derived from grape stalks as a sustainable adsorbent for removing diclofenac (DCF), a widely used pharmaceutical and persistent water micropollutant that poses significant environmental risks if not effectively eliminated. Hydrothermal carbonization (HTC) was applied at three temperatures (200, 230, and 260 °C) to synthesize hydrochar. To further enhance its adsorption properties, the hydrochar was subjected to physical activation by steam. Comprehensive characterization, including SEM, TEM, BET analysis, and elemental composition, revealed significant chemical and morphological changes and the formation of a multy-layered porous structure, especially after steam activation. Adsorption experiments were performed under constant stirring at 100 rpm for about 24 h at room temperature. The influence of different hydrochar dosages (0.2-1.0 g L^{- 1}) on the process was evaluated. The adsorption tests demonstrated that the hydrochar produced at 230 °C exhibited superior DCF removal efficiency, which was further enhanced post-activation, achieving a removal rate of up to 99.2% under optimized conditions. The experimental data for DCF adsorption onto the steam-activated hydrochar closely followed the Langmuir model, with a maximum capacity of 25.19 mg g^{- 1}. Additionally, the pseudo-second-order model showed the best agreement with the experimental data. The steam-activated hydrochar derived from agricultural waste has great potential as an efficient and cost-effective adsorbent for removing DCF, addressing key challenges in water pollution and waste management.