Denitrification of nitrite by ferrous hydroxy complex: Effects on nitrous oxide and ammonium formation

• Ferrous hydroxy complex was employed as an excellent reductant for nitrite.
• The production of nitrous oxide and ammonium highly depends on the dosage of Fe2+, oxygen, OH− and trace metals.
• Decreasing the yield of ammonium and increasing the removal rate of TN.
• The presence of trace metals accelerate the nitrite reduction.

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.

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