Nitrite reduction by structural Fe(II) associated with ferrous hydroxy complex (FHC) was performed in a batch reactor. The optimum Fe(II) : OH- molar ratio for nitrite reduction is 7:12. FHC could totally remove nitrite within 60 min when the Fe(II) : NO2- molar ratio exceeded 10. Less than 30% of the removed nitrite was transformed to ammonium after 1.0 h when the Fe(II) : NO2- molar ratio was below 20, and the percentage of NH4+-N in the products increased with increasing Fe(II) : NO2- molar ratio. However, more than 80% of the nitrite was reduced to ammonium when the Fe(II) : NO2- molar ratio was more than 50. Nitrite tended to be transformed to ammonium under high pH conditions, with a decline in the removal rate. The presence of oxygen reduced the production of ammonium. The addition of Cu2+ or Zn2+ might enhance the removal of nitrite and reduce NH4+-N production and increase N2O production. (C) 2015 Elsevier B.V. All rights reserved.