In a recent article published in Scientific Reports, Lucio Zaccariello, Annarita Travaglino, and colleagues detail a sustainable and cost-effective approach to tackling a pervasive global water contamination problem: the presence of diclofenac (DCF). DCF, a common non-steroidal anti-inflammatory drug, is a polar and highly soluble pharmaceutical micropollutant. Because conventional wastewater treatment plants (WWTPs) can’t fully remove it, DCF continuously accumulates in water bodies worldwide, posing risks to aquatic ecosystems and human health. This research successfully converted grape stalks, an abundant byproduct from the wine industry, into a highly effective adsorbent called steam-activated hydrochar, ultimately achieving a DCF removal rate of up to 99.2%. The motivation behind this work aligns with a global need for resource preservation and waste valorization, turning a large-volume agricultural waste product—which otherwise poses disposal challenges—into a valuable purification tool.

The first step in generating this potent adsorbent involved hydrothermal carbonization (HTC) of the grape stalks, a thermochemical process chosen because it doesn’t require pre-drying the wet biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More, making it energy efficient. The team tested the HTC process in a larger, 3 L reactor, a valuable approach for scaling up operations, at three temperatures: 200, 230, and 260∘C. Initial adsorption tests on the pristine hydrochars showed that the material produced at 230∘C (HC-230) was superior, yielding a DCF removal efficiency of 21.1% and an adsorption capacity of 1.08 mg/g. The higher temperature of 260∘C actually hurt performance, resulting in a lower removal rate of 14.7%. Structural analysis confirmed this: the 230∘C temperature created a desirable, well-organized nanometric sphere structure. Going higher, to 260∘C, caused structural deterioration, likely from over-carbonization, reducing the beneficial surface area.

Despite its initial advantage, the HC-230’s raw performance was still too low, so it was subjected to physical activation with steam at 900∘C for 15 min to create the steam-activated hydrochar (SA-HC-230). This step dramatically improved the material’s surface properties, notably increasing its specific surface area (SBET​) from 49.41±0.51 m2/g to a massive 728±5 m2/g. The activation process resulted in a multi-layer flake superstructure of organized nanospheres that homogeneously covered the surface. With this enhanced structure, the SA-HC-230 achieved a maximum DCF removal efficiency of 99.2% at a 1.0 g/L dosage.

Adsorption kinetics were best described by the pseudo-second-order model (R2>0.998), indicating that chemisorption, involving valence forces like electron sharing or exchange, is the primary rate-limiting step. The equilibrium data fit the Langmuir isotherm model best (R2=0.9709), which suggests DCF adsorption occurs mainly as a monolayer coverage on a homogeneous surface. The maximum monolayer adsorption capacity (qmax​) was determined to be 25.19 mg/g. Despite the material’s surface having a negative charge ( pHpzc​=7.1) and DCF being in its anionic form at the operating pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More (∼9.0), resulting in expected electrostatic repulsion, the high removal efficiency suggests that non-coulombic forces—such as π-π stacking between the aromatic rings of DCF and the hydrochar’s graphitic regions, hydrogen bonding, and hydrophobic effects—play a significant, synergistic role. The large SBET​ and mesoporous structure also support a contribution from pore-filling mechanisms.

Beyond its high efficiency, the SA-HC-230 demonstrated excellent reusability, maintaining a DCF removal efficiency of greater than 95% after five successive adsorption-desorption cycles. This exceptional performance, coupled with the low-cost grape stalk feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More, confirms the material’s viability as an economically and environmentally advantageous option for sustainable water treatment.

Source: Zaccariello, L., Travaglino, A., Fenti, A., Falco, G., Galoppo, S., Palma, D., Giarra, A., Toscanesi, M., Trifuoggi, M., & Iovino, P. (2025). Steam activated hydrochar from wine waste for the removal of pharmaceutical micropollutants from water. Scientific Reports, 15(34169). https://doi.org/10.1038/s41598-025-15211-5