Adsorption of ammonia nitrogen from the synthetic wastewater on chemically modified carbon felt

To remove ammonia nitrogen from synthetic wastewater, carbon felt (CF) was modified with potassium chlorate, sulfuric acid, sodium persulfate, and sodium hydroxide. The specific surface area and the pore volume of CF after modification individually increased 1.27 and 1.06 times more than pristine CF, resulted in the improvement of ammonia nitrogen adsorption efficiency superior to pristine CF. Under the optimal conditions—specifically, a dosage of 25 g/L, a synthetic wastewater pH of 5.5, an adsorption time of 240 min, and an initial ammonia nitrogen concentration of 5 mg/L at 25 °C—, the removal efficiency reached 72.8±3.4%, with an adsorption capacity of 0.153±0.013 mg/g. As the initial concentration of ammonia nitrogen increased from 5 mg/L to 200 mg/L, the removal efficiency correspondingly decreased from 72.8±3.4% to 12.5±0.7%, while the adsorption capacity increased from 0.153±0.013 mg/g to 1.052±0.043 mg/g. After seven regeneration cycles at a voltage of 2 V and a charging time of 1 min, the recovery rate of modified CF was 88.1±1.2%, with an ammonia nitrogen removal efficiency of 65.9±1.6%. The adsorption process was described by the Langmuir isotherm and pseudo-second-order kinetic models, indicating that it is characterized by homogeneous monolayer adsorption primarily driven by chemisorption. The ammonia nitrogen adsorption process on modified CF is exothermic and is characterized by a gradual decrease in adsorption rate.