Elucidating the role of carbon shell in autotrophic denitrification driven by carbon-coated nanoscale zerovalent iron

• NO 3 -N and TN are removed by 95% and 84% without NO 2 -N detected. • CS isolates Fe 0 from NO 3 -N to alleviate biological and chemical competition. • Fe 0 @C shows high electron selectivity in wide range of pH, temp. and NO 3 -N. • H 2 is the main electron donor and dominates the autotrophic denitrification. • The sustained electrons released from Fe 0 @C promote TN removal capacity by Fe 0 @C. Iron-carbon micro-electrolysis (IC-ME) can promote Fe 0 corrosion to provide H 2 or e − as electron donors for autotrophic denitrifier under organic-limited wastewater, but also stimulate the chemical reduction of NO 3 -N to undesired NH 4 -N. Therefore, it is still a challenge to optimize the eletron pathways provided by Fe 0 to improve its eletron selectivity for biodenitrification. Herein, a Carbon-coated Iron (Fe 0 @C) Autotrophic Denitrification (CCIAD) system was first established to achieve higher removal efficiency of NO 3 -N (95%) and TN (84%) without NO 2 -N accumulation, and the role of carbon shell (CS) in Fe 0 @C was systematically evaluated. Hydrophobic CS could prevent iron oxidation from oxygen and isolate Fe 0 from NO 3 -N to alleviate the competition of biological and chemical processes for reducing nitrate. In addition, the CS promoted e − generation, while inhibited the adsorption of NO 3 -N, thereby increasing the H 2 production. Therefore, the assembly of carbon coated Fe 0 regulated the electron pathway so that H 2 became the main electron donor and dominated the autotrophic denitrification, thereby improving the electron efficiency of Fe 0 (82.7%). The sustained electron release of Fe 0 @C improved its TN removal capacity (78 mg N/g Fe). This study shed light on the electronic pathways provided by Fe 0 @C and advanced our understanding of Fe 0 @C-based bio-denitrification for the purpose of next-generation Fe 0 design.