Antibiotic mitigation of aqueous systems using untapped potential of unsorted garden waste-derived biochar:...

The unchecked consumption of antibiotics leads to the persistence of their active form residues in the environment, perpetuating the cycle of exposure, selection and re-infection, which ultimately exacerbates the environmental antimicrobial resistance (AMR). This work aims to provide a direct comparison of different heterogeneous and underutilised biomass as antibiotic adsorbents. This study investigates the adsorption of the antibiotic, specifically Ciprofloxacin (CIP), by biochars produced from two underutilised biomass sources-unsorted Garden waste (GW) and Cashew nut shells (CNS)-at different temperatures (500-700 °C) and residence times (1-2 h). Based on initial adsorption screening and thermogravimetry, GW biochar, produced at 700 °C with a 2-h residence time (GW700 °C/2 h), was selected as the most suitable. A detailed analysis of this biochar was carried out: TGA confirmed the thermal stability; proximate analysis confirmed a high fixed carbon content; BET analysis (59.11 m² g ¹), FTIR, and XRD indicated the presence of relevant functional groups, and FE-SEM displayed a porous surface morphology, all of which substantiate the adsorption performance. Furthermore, optimum sorption conditions were determined through batch studies, and 50 mg GW700 °C/2 h biochar was found to remove 85.4% of 5 mg L^-1 CIP in 285 min at a neutral pH. Kinetic and isotherm data confirmed multilayer chemisorption with a maximum sorption capacity of 6.19 mg g^-1. This is the first report exploring unsorted GW biochar as a sustainable solution for antibiotic mitigation, which, in future, can be scaled up to be part of the wastewater treatment systems.