Co-adsorption performance and mechanism of ammonium and phosphate by iron-modified biochar in water

Abstract

To recover nitrogen and phosphorus from water bodies and reduce their potential risk of causing eutrophication, high-temperature pyrolysis-produced biochar (HBC) modified by ferric chloride (Fe-HBC) was adopted to investigate its surface modification on the co-adsorption performance of nitrogen and phosphate. In comparison to HBC, Fe-HBC exhibited superior specific surface area, well-developed pore structure, and enriched surface functional groups while successfully loading Fe2+ and Fe3+. It has been determined that the co-adsorption mechanism of ammonium and phosphate by Fe-HBC involves a combination of pore filling, ion exchange, functional group coordination, electrostatic attraction, and coprecipitation. The results from the batch adsorption experiments indicate that the ammonium adsorption capacities for Fe-HBC1, Fe-HBC2, and Fe-HBC3 were 10.59 mg/g, 10.38 mg/g, and 7.59 mg/g, respectively, while the phosphate adsorption capacities were 13.46 mg/g, 10.46 mg/g, and 15.22 mg/g, respectively. The results of the column adsorption experiments showed that too high or too low biochar percentage and flow rate were not conducive to improving the adsorption capacity of the adsorption column, and the maximum adsorption capacity of the adsorption column was achieved at a biochar percentage of 1 % and a flow rate of 1 mL/min. This study demonstrates the potential of this iron-modified biochar derived from agricultural wastes for practical application in the removal of ammonium and phosphate from wastewater.