Study on the Adsorption Performance of Nitrite Nitrogen by Biomass Ash Filter Media

This study explores the utilization of biomass ash as a raw material to prepare a novel block-shaped filter material with a well-developed pore structure and stable chemical properties via short-term high-temperature sintering. Its adsorption performance for nitrite nitrogen was investigated, along with the adsorption kinetics and thermodynamic behaviors. The results of the static adsorption experiments show that the biomass ash filter achieved higher nitrite adsorption per unit under conditions of high nitrite nitrogen concentration, moderate adsorption temperatures and adsorption time, and low solid-liquid ratio. The maximum unit adsorption capacity (6.78 mg/g) was achieved under the following conditions: an initial concentration of 65 mg/L, an adsorption temperature of 35 °C, an adsorption time of 80 min, a pH of 3, and a solid-liquid ratio of 1:400 (g:mL). The filter material surface exhibited a heterogeneous structure. Adsorption of nitrite nitrogen was identified as a spontaneous endothermic reaction involving both multilayer physical adsorption and monolayer/multilayer chemical adsorption, with the former predominating. Under dynamic conditions, the unit adsorption capacity was 32.02%, 52.69%, and 58.15% higher than those of coconut shell biochar, ceramic pellets, and natural zeolite, respectively. This indicates excellent adsorption properties, enabling water purification while achieving biomass ash disposal and recycling, making it highly valuable for promotion.