Effects of Fe(II) and Fe(III) on the single-stage deammonification process treating high-strength reject water from sludge dewatering

► Fe2+ incorporation for single-stage deammonification process was linearly correlated with NH4+-N removal under conditions of Fe2+ and Fe3+ in the influent below 1.3 mg/L and 0.4 mg/L. ► Excess Fe2+ and Fe3+ decreased the sludge activity, the sludge concentration and the amount of functional microbiological community. ► The sequence of sensitivity to iron was assessed to autotrophic anammox bacteria > autotrophic aerobic ammonium oxidizers > hetetrophic denitrifiers. ► Extracellular substance as the likely sites for iron uptake was largely released at high iron concentrations.