Sustainable phosphate and ammonium recovery using modified-chitosan cow dung biochar

The intensification of cattle husbandry generates nutrient-rich wastewater containing high levels of phosphorus and ammonium, which contribute to eutrophication and water pollution. Addressing this problem requires effective nutrient removal, recovery, and reuse. The objective of this study was to develop a sustainable strategy for nutrient valorisation through the synthesis of a controlled-release fertiliser based on magnesium-impregnated cow dung biochar encapsulated in a chitosan biopolymer matrix (CH@Mg/CD). The composite was prepared via pyrolysis and magnesium impregnation, and its structural and functional properties were confirmed using Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscope analyses. Batch adsorption experiments, conducted in triplicate, were evaluated under varying pH, dosage, contact time co-existing ions, and initial concentrations, with kinetic and isotherm modelling applied. The CH@Mg/CD composite exhibited high adsorption capacities of 36.02 mg/g for phosphate and 23.88 mg/g for ammonium, fitting well with the pseudo-second-order kinetic and Langmuir isotherm models. These findings demonstrate the superior nutrient capture efficiency of the composite compared to conventional materials. In conclusion, CH@Mg/CD offers a cost-effective and environmentally viable solution for wastewater treatment while promoting circular bioeconomy through its application as a high-performance fertiliser.