Magnetic activated carbon for oxytetracycline removal from livestock drinking water

Oxytetracycline (OTC) is a broad-spectrum antibiotic widely used in animal husbandry to prevent and treat infections in livestock. A significant fraction of administered OTC can be excreted unmetabolized, raising serious environmental concerns due to the dissemination of antibiotic residues and the potential development of antibiotic-resistant pathogens in surface and livestock drinking water. This study focuses on the synthesis of magnetic activated carbon (MAC), the evaluation of its OTC removal efficiency and the assessment of its magnetically assisted separation from livestock drinking water formulated according to the Food and Agriculture Organization technical guidelines. The results demonstrate that MAC exhibits substantially enhanced performance compared to conventional activated carbon (AC). Specifically, MAC achieved approximately twice the OTC removal efficiency of AC and enabled a dramatic reduction in sedimentation time when assisted by an external magnetic field, decreasing settling from 6 h to approximately 1 min. Under FAO-recommended ranges of pH, ionic strength, and hardness for livestock drinking water, MAC containing 5% magnetic nanoparticles showed, on average, a 24% higher OTC removal capacity than AC. Adsorbent dosage was identified as the dominant factor influencing OTC removal, although water physicochemical conditions also played a significant role. Both MAC5% and AC exhibited maximum adsorption efficiency at neutral to slightly acidic pH and at low concentrations of NaCl and CaCO₃. MAC5% achieved nearly 100% higher OTC removal than AC at moderately saline and hard water conditions (pH = 8, [NaCl] = 60 mg l^-1, [CaCO₃] = 300 mg l^-1). At high salinity and hardness levels ([NaCl] = 6000 mg l^-1and [CaCO₃] = 500 mg l^-1), the adsorption efficiencies of MAC5% and AC became comparable. In terms of solid-liquid separation, the application of an external magnetic field markedly improved MAC5% settling efficiency, independently of pH, salinity, and hardness, confirming its suitability for rapid and efficient water treatment applications.