Enhanced electron transport and selective reduction of nitrate to nitrogen by sludge biochar-supported nanoscale zero-valent iron

In the process of nitrate reduction by nano zero-valent iron (nZVI), the preparation of nZVI/sludge biochar (nZVI/SBC) by introducing SBC will help to improve the aggregation and low nitrogen selectivity. Herein, the pyrolysis temperature of SBC was changed, and the excellent reduction capacity with the minimum charge transfer resistance were obtained at 300 °C. In addition, nZVI/SBC prepared with a mass ratio of 1:1 obtained a nitrate removal efficiency of 95.23 % and a nitrogen selectivity of 35.33 %. The corrosion of Fe⁰ at the appropriate ratio provided sufficient electrons for the reduction, and the further transformation into Fe₃O₄ promoted the outward transport of electrons. The electrons were transferred to the solid surface through the SBC, which promoted the accumulation and collision of nitrogen intermediates and induced the production of nitrogen. The nitrate removal efficiency of nZVI/SBC remained above 66 % in the wide pH range (3.0–11.0), which demonstrated practical nitrate remediation capabilities.