Unacclimated activated sludge improved nitrate reduction and N₂ selectivity in iron filling/biochar systems

Iron (Fe)-based denitrification is a proven technology for removing nitrate from water, yet challenges such as limited pH preference range and low N₂ selectivity (reduction of nitrate to N₂) persist. Adding biochar (BC) can improve the pH preference range but not N₂ selectivity. This study aimed to improve nitrate reduction and N₂ selectivity in iron filling/biochar (Fe/BC) systems with a simplified approach by coupling unacclimated microbes (M) in the system. Factors such as initial pH, Fe/BC ratio, and Fe/BC dosage on nitrate removal efficiency and N₂ selectivity were evaluated. Results show that the introduction of microbes significantly enhanced nitrate removal and N₂ selectivity, achieving 100 % nitrate removal and 79 % N₂ selectivity. The Fe/BC/M system exhibited efficient nitrate reduction at pH of 2-10. Moreover, the Fe/BC/M system demonstrated an improved electrochemical active surface area (ECSA), lower electron transfer resistance and lower corrosion potential, leading to enhanced nitrate reduction. The high i₀ value in Fe/BC/M system means more H_ads could be generated, thus improving the N₂ selectivity. This study provides valuable insights into a novel approach for effective nitrate removal, offering a potential solution to the environmental challenges posed by excessive nitrate in wastewater, surface water and ground water.