Removal of nitrogen and phosphorus pollutants from water by FeCl3- impregnated biochar

Chemical fertilizers and pesticides used are currently increasing alongside the human population grew and agriculture spread, resulting in high nitrogen (TN) and phosphorus (TP) contents in farmland soil and the surrounding water-bodies. Fabricating economic but effective metal impregnated biochar, as a sorbent to remove inorganic pollutants from water, is important to prevent eutrophication. In the present work, iron-loaded biochar was prepared by impregnating by FeCl₃ and following pyrolyzing at 550 °C. The chemical functional groups, surface morphologies, and internal crystal structures of the Fe-loaded biochar (FeB) were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and X-ray diffraction, respectively. Results indicated that the preparing process induced a layer of Fe oxide at the surface of biochar, and changed the surface morphology and internal crystal structure. The FeCl₃ content in soaking solution had remarkable effects on pore structure formation, surface morphology features and removal efficiencies of TN and TP from wastewater by biochar. The Langmuir model indicated that 1%-Fe impregnated biochar (B1) and the 10%-Fe impregnated biochar (B10) exhibited maximum adsorption capacity of TN and TP, which reached to more than 14 mg/g for TN and 90 mg/g for TP, respectively. B10 could remove over 85% of TP from artificial wastewater and less than 0.5% of TP was released in desorption experiments. Similarly, B1 could remove 60% of TN while only 1% was released in desorption experiments. B1 and B10 could remove 50% of TN and 80% of TP from the actual agricultural wastewater, respectively. This confirmed that Fe-impregnated biochar could effectively remove inorganic nutrients from wastewater and seal them in the prevention of secondary pollution. The FeB was characterized by FT-IR and SEM before and after its application as an adsorbent in agricultural wastewater, and results revealed that the removal of TN and TP was primarily attributed to the well-developed pore structure and the Fe oxides fixed on the surface of biochar. Inorganic nitrogen and phosphorus in wastewater are removed by surface complexation, coprecipitation, electrostatic interaction and ion exchange. In conclusion, the present work demonstrated that the FeB is an effective adsorbent for removing TN and TP pollutants from nutrient-rich wastewaters.