Biomass-derived hydrochar and activated carbon in pharmaceutical pollution mitigation: a comprehensive overview

Hydrochar, a carbonaceous material produced from biomass via hydrothermal carbonization (HTC), has emerged as a sustainable adsorbent for mitigating pharmaceutical pollution in wastewater. Unlike pyrochar and hydrochar-derived activated carbon (HDAC), hydrochar is synthesized at lower temperatures (180-250 °C) using wet biomass, reducing energy consumption and enabling valorization of high-moisture waste without costly drying processes. Its rich oxygenated functional groups and tunable surface chemistry enhance the adsorption of polar contaminants through mechanisms such as hydrogen bonding, π-π interactions and hydrophobic effects, offering advantages over the more aromatic, less functionalized pyrochar. Hydrochar and HDAC demonstrate significant potential for removing pharmaceutical pollutants, with enhanced performance achievable through tailored preparation and activation methods that optimize their surface properties. Hydrochar derived from horse manure exhibits a low adsorption capacity of 1.8 μg g^-1 for ciprofloxacin, attributed to its limited specific surface area (SSA) of 4.62 m² g^-1. In contrast, ZnCl₂-activated HDAC with an SSA of 1326 m² g^-1 achieves a significantly higher capacity of 416.7 mg g^-1, driven by π-π interactions and chemisorption. Similarly, KOH activation of grape seed-derived hydrochar enhances the capacity to 650.8 mg g^-1 for sulfamethoxazole. Despite these advancements, challenges persist, including non-selective adsorption, pH sensitivity (optimal range of 6-8) and limited regeneration efficiency, with a capacity reduction of 18-23% after five cycles. Despite its potential, challenges such as non-selective adsorption, pH sensitivity and limited regeneration efficiency remain. This review highlights hydrochar and HDAC's versatility and sustainability, advocating for further research to refine activation methodologies, optimize regeneration techniques and scale its application in pharmaceutical wastewater treatment. By incorporating hydrochar into sustainable wastewater management frameworks, it is feasible to mitigate the environmental impact of pharmaceutical pollution effectively.