An enriched biomass was developed from municipal sewage sludge consisting of three dominant bacteria, representing the genera of Enterobacter, Citrobacter and Streptomyces. The biomass was used in a series of batch experiments in order to determine kinetic constants associated with biomass growth and NOx reduction in aqueous Ferrous EDTA/NTA solutions and Ferric EDTA/NTA solutions using ethanol as organic electron donor. The maximum specific reduction rates of NOx in Ferrous EDTA and Ferrous NTA solutions were 0.037 and 0.047 mMoles L-1 d(-1) mg(-1) biomass, respectively while in Ferric EDTA and Ferric NTA solutions were 0.022 and 0.024 mMoles L-1 d(-1) mg(-1) biomass, respectively. In case of Ferric EDTA/NTA solution, the kinetic constants associated with reduction of Ferric EDTA/NTA to Ferrous EDTA/NTA were also evaluated simultaneously. The maximum specific reduction rates of Ferric EDTA and Ferric NTA were 0.0021 and 0.0026 mMoles L-1 d(-1) mg(-1) biomass. The significance of these observations are presented and discussed in this paper. (C) 2012 Elsevier Ltd. All rights reserved.