Kinetics of FeS-mediated denitrification in sediments from the Camargue (Rhone delta, southern France)

Denitrification rates were measured in sediments after the addition of different concentrations of FeS. A decrease of the denitrification rate was observed when high concentrations of ferrous iron (> 10 mM) were present. In the experiments with no significant concentrations of free Fe2+, the relationship between NO3− reduction and FeS concentration followed Michaelis and Menten kinetics. The maximum rate was 0.273 mmol l−1 d−1, 6 times as much as the basal rate 0.046 mmol l−1 d−1, which was attributed to organic matter; the Ks was 1.45 mM FeS. The stoichiometry of the overall reaction involving NO3− reduction and the concomitant S2− oxidation was also investigated. Measured ΔS/ΔN ratios ranged between 0.55 and 0.64, with ΣH2S + SO42− changing less than 10%. These values agree with the theoretically expected value of 0.56.