Fe(III)EDTA and Fe(II)EDTA-NO reduction by supported (nano)ZVI in Fe(II)EDTA complexation denitrification technology: Performance, kinetics, and pathway

Fe(II)EDTA shows superior ability in complexing absorption denitrification; however, the resulting Fe(II)EDTA-NO and its easy oxidation to Fe(III)EDTA decimate its role. Rapid Fe(II)EDTA regeneration from Fe(II)EDTA-NO and Fe(III)EDTA reduction is important for effective and successive nitrogen oxide removal, and harmless N2 is desirable as the major N-containing product. This study investigated the performance, kinetics, and pathway of Fe(III)EDTA and Fe(II)EDETA-NO reduction by four supported (nano)ZVI ((nanoscale) zero-valent iron)) and NO removal coupled with Fe(II)EDTA regeneration. Support-mediated the physicochemical and structural properties of loaded (nano)ZVI, Fe(III)EDTA and Fe(II)EDTA-NO adsorption, and reduction pathways are closely related to the efficiency, rate, and product selectivity. Activated carbon-supported nano-ZVI (AC-nZVI) is important for Fe(III)EDTA and Fe(II)EDTA-NO reduction with high efficiencies of 89.8 % and 88.2 % within 5 min and 30 min, respectively, and high N2 selectivity (52.98 %), outperforming most of the reduction systems reported previously. The pathway alternation induced by the catalysis of activated carbon and micro-electrolysis of iron–carbon is the origin of highly efficient and selective AC-nZVI for Fe(III)EDTA and Fe(II)EDTA-NO reduction. Resilient over a wide O2 content (0–10 %), pH (3–8), and temperature range (20–50 °C) and efficient for NO removal with large capacity coupled with Fe(II)EDTA regeneration, AC-nZVI would be applicable in industrial Fe(II)EDTA regeneration in Fe(II)EDTA complexation denitrification technology. This study proposes an alternative for Fe(II)EDTA regeneration and provides insights into the mediation of the performance, kinetics, and pathway for guiding reduction system design.