Abstract
Biological reduction of nitric oxide (NO) to di‐nitrogen (N~2~) gas in aqueous Fe(II)EDTA^2−^ solutions is a key reaction in BioDeNOx, a novel process for NOx removal from flue gases. The mechanism and kinetics of the first step of NO reduction, that is, the conversion of NO to N~2~O, was determined in batch experiments using various types of inocula. Experiments were performed in Fe(II)EDTA^2−^ medium (5–25 mM) under BioDeNOx reactor conditions (55°C, pH 7.2 ± 0.2) with ethanol as external electron donor. BioDeNOx reactor mixed liquor gave the highest NO reduction rates (±0.34 ${\rm nmol},{\rm s}^{ - 1} ,{\rm mg}_{{\rm prot}}^{ - 1} $) with an estimated K~m~ value for NO lower than 10 nM. The specific NO (to N~2~O) reduction rate depended on the NO (aq) and Fe(II)EDTA^2−^ concentration as well as the temperature. The experimental results, complemented with kinetic and thermodynamic considerations, show that Fe(II)EDTA^2−^, and not ethanol, is the primary electron donor for NO reduction, that is, the BioDeNOx reactor medium (the redox system Fe(II)EDTA^2−^/Fe(III)EDTA^−^) interferes with the NO reduction electron transfer chain and thus enhances the NO denitrification rate. Biotechnol. Bioeng. 2008;100: 1099–1107. © 2008 Wiley Periodicals, Inc.