Valorization of waste-derived coffee husk into a sustainable adsorbent for multicomponent pharmaceutical removal from complex wastewater under continuous-flow conditions

Abstract

This study elucidates the competitive adsorption dynamics of ciprofloxacin (CIP) and acetaminophen (ACE) onto coffee husk activated with potassium (CH–KOH, BET surface area = 1145 m² g⁻¹, pH_PZC = 7.36), providing mechanistic insights into the removal of pharmaceuticals in complex aqueous matrices. The Modified Langmuir multicomponent isotherm effectively captured the competitive equilibrium behavior (deviation = 25.8%), showing a higher affinity for ACE (η_ACE = 0.7) than for CIP (η_CIP = 4.9), the qT was 1.25 mmol g⁻¹ across the entire evaluated concentration range, which is similar to the observed in mono-component systems, Q_max 1.26 mmol g⁻¹ for ACE and 0.58 mmol g⁻¹ for CIP, with removal efficiencies of 91–99% and 75–99%, respectively. In real matrices such as synthetic hospital wastewater and urine, high efficiencies (84–97%) were maintained. Fixed-bed column studies confirmed the strong performance under continuous-flow conditions, with saturation capacities (q_s) up to 1.46 mmol g⁻¹ for ACE and 0.61 mmol g⁻¹ for CIP, mass transfer zones ranging from 0.42 to 1.53 cm, and breakthrough times between 91 and 1463 min depending on flow rate (1–3 mL min⁻¹) and bed height (1–3 cm). The Thomas model accurately predicted breakthrough curves, revealing faster kinetics for ACE. Physisorption predominates, involving synergistic π–π stacking interactions, hydrogen bonding networks, and hydrophobic association, with ACE showing greater selectivity in both mono and multicomponent systems. CH–KOH exhibited high stability and reusability, stabilizing at approximately 70% of its initial capacity by the third cycle, with no further decrease observed in the fourth cycle. Comprehensive physicochemical characterization revealed that physisorption predominates, involving synergistic π–π stacking interactions, hydrogen bonding networks, and hydrophobic associations. These results confirm the potential of CH–KOH as a sustainable adsorbent for pharmaceutical contaminant removal in real-world scenarios, integrating circular economy principles into advanced water treatment.