Pharmaceutical adsorption and ex-situ electro-regeneration performance of magnetically modified activated carbon

This study investigated the impact of iron (Fe) modification on the physicochemical and adsorption properties of powdered activated carbon (M-PAC) for pharmaceutical removal, as well as the ex-situ electro-regeneration of pharmaceutical-laden M-PAC. The objectives were to (i) examine the adsorption capacity of Fe-modified M-PAC for ciprofloxacin (CIP) and ibuprofen (IBU) in deionized water, (ii) assess adsorption capacity in wastewater effluent, and (iii) evaluate ex-situ electro-regeneration of spent M-PAC. Fe-modification improved PAC's settling velocity by 1.7 times compared to pristine PAC, enabling easier separation without filtration or coagulation/flocculation, which benefits regeneration processes. M-PAC also exhibited more linear adsorption isotherms than pristine PAC, offering consistent and predictable adsorption behavior across varying CIP and IBU concentrations. In wastewater effluent, adsorption decreased by 28% for CIP and 67% for IBU due to stronger competition from effluent organics. Despite this reduction, Freundlich adsorption capacities of 28.7 mg/g for CIP and 15.47 mg/g for IBU were achieved. Electro-regeneration restored up to 100% of adsorption capacity within 60-180 min over a single regeneration cycle. IBU desorbed rapidly within the first hour, while CIP required longer treatment due to stronger interactions with the carbon surface. In mixed-solute systems, regeneration efficiency was reduced by approximately 25% for IBU and up to 65% for CIP, likely from competitive desorption and differing molecular affinities for M-PAC. The calculated energy consumption for electro-regeneration of spent M-PAC was < 0.2 kWh/g, making it more competitive than existing regeneration methods. Overall, the results demonstrate that Fe-modification enhances PAC's separation and adsorption characteristics while enabling effective ex-situ electro-regeneration. Adsorbent surface properties, along with pharmaceutical molecular structure, charge, and polarity, critically influence adsorption behavior and regeneration kinetics. These findings highlight the potential of Fe-modified PAC as a reusable adsorbent for pharmaceutical removal in water treatment.