Synergistic adsorption and removal of nitrate in an electrically polarized column packed with AlCl3-modified activated carbon

Adsorption is an efficient approach for nitrate removal and recovery, yet its application is constrained by limited adsorption capacity. This study introduces an electrically polarized packed column that enhances adsorption while simultaneously removing nitrate through redox reactions. An AlCl₃ modification method was developed, significantly improving the nitrate adsorption capacity of activated carbon (AC) by nearly two-fold. The electrically polarized column packed with AlCl₃-modified AC (E-Al/AC) achieves a treating capacity of 83 bed volume (BV) at a short hydraulic retention time (HRT) of 7 min, which is more than 9-fold of the value of the column packed with raw AC without electric stimulation (9 BV). Mechanistic studies revealed that the combined effect of functional groups (i.e., Al and Cl groups) and electric field contribute to the enhanced adsorption capacity. In addition, the nitrate ions were efficiently reduced to ammonia on the cathode, which was subsequently oxidized to nitrogen gas by the electrochemically generated chlorine radicals (Cl). The E-Al/AC reactor also exhibits stable nitrate removal performance after multiple regeneration cycles, indicating its promising potential for the remediation of nitrate-contaminated groundwater and wastewater. This system provides valuable insights into the development of cost-effective denitrification and nitrogen recovery technologies.